Independent report

Animal Welfare Committee (AWC): Opinion on breeding and breeding technologies in commercial livestock agriculture

Published 23 April 2026

Introduction and scope

1. The Animal Welfare Committee (AWC) has been asked to produce a new report on the Welfare Implications of Animal Breeding and Breeding Technologies in Commercial Agriculture.

2. The AWC has been asked to include modern breeding technologies in its analysis, encompassing ‘precision breeding’.

3. The scope of this Opinion covers dairy cattle, beef cattle, sheep, pigs, meat chickens, laying hens, turkeys, and salmon (the same species which were considered in the 2012 Farm Animal Welfare Committee (FAWC) report on the Welfare Implications of Animal Breeding and Breeding Technologies in Commercial Agriculture (see below)). Due to the wide remit, specific welfare aspects such as housing conditions, transportation or management of new-borns and youngstock are not comprehensively reviewed.

Background

4. The AWC’s predecessor, the Farm Animal Welfare Committee (FAWC), directly addressed the topic of breeding for the first time in their 2004 report on ‘the Welfare Implications of Animal Breeding and Breeding Technologies in Commercial Agriculture’. This was followed by a second report on this subject in 2012 that emphasised that breeding programmes and technologies should support the concept of ‘a life worth living’. They commended the progress that livestock breeding companies had made in incorporating some health and robustness metrics into their breeding programmes. However, they noted that some significant challenges remained. In particular, they had found that genomic selection had predominantly focused on easily measurable production traits and often overlooked more complex functional health and fitness characteristics that may only become apparent later in an animal’s life. They highlighted that there was a need to introduce more comprehensive screening methods that could assess these harder-to-measure traits. They raised concerns that if these were not introduced, there was a risk that animal welfare could be compromised in the long term.

5. In the 13 years since that report was published there have been significant developments both in approaches to livestock breeding and in the technologies used to facilitate such approaches. This is particularly true in relation to the use of technologies that would be regulated by the Genetic Technology (Precision Breeding) Act 2023. Through its recognition of the potential of breeding goals to impact animal health and welfare, that Act has drawn attention to the possible impacts of all breeding practices (not just those using modern technologies) and the need to mitigate negative and promote positive welfare outcomes. It is in the context of such developments and public interest in them that government has asked the AWC to produce this new Opinion on the Welfare Implications of Animal Breeding and Breeding Technologies in Commercial Agriculture.

6. In the production of this Opinion, the AWC has selected specific examples from different species to illustrate the breadth of welfare issues (both positive and negative) associated with breeding and breeding technologies.

Evidence gathering

7. Whilst compiling this Opinion, the AWC have relied not only on peer-reviewed academic research, but also on input from a range of stakeholders including breeding companies, farmers, industry groups, breed societies, veterinary bodies, academics, non-governmental organisations (NGOs) and animal welfare lobby groups (see Appendix 4). The information gathered has been obtained from a systematic review of the academic literature (Johansen and Arnott, 2024), written submissions, site visits, roundtable discussions with stakeholders and a review of grey literature (see Appendices 2,4 and 5).

8. The Defra-commissioned systemic academic review critically examined relevant peer-reviewed literature produced between 2011 and March 2024 (Johansen and Arnott, 2024). It used a validated scientific method that searched a number of scientific databases with key search terms that related to both breeding and breeding technologies and the potential welfare effects of these for the species covered in this opinion. Following the initial database search, 405 relevant papers were identified and analysed in detail.

9. The AWC is aware that while peer-reviewed academic research is fundamental, many studies focus on short-term effects and may lack long-term welfare impact assessments. In addition, they often focus on relatively small numbers of animals kept under specific conditions. Thus, these often cannot truly reflect the breadth of different environments and management regimes used within the UK livestock industry.

10. Industry stakeholders have driven significant technical improvements and scientific knowledge through their breeding programmes. Although much of this work has not been published in peer-reviewed academic journals, it is common for breeding companies to share their findings with livestock keepers through knowledge exchange initiatives and industry publications. This alternative approach in both collecting and disseminating results does not diminish the importance of these contributions — rather, it underscores the necessity for continued engagement between stakeholders, academics and policy makers.

Legal context

Legislation

11. Under section 4 of the Animal Welfare Act 2006 (which applies in England and Wales) and section 19 of the Animal Health and Welfare (Scotland) Act 2006, it is an offence for a person to cause or permit unnecessary suffering to any domesticated animal for which they are responsible, including when breeding livestock. Under the same Acts, sections 9 and 24 respectively, a person commits an offence if they do not take such steps as are reasonable in all the circumstances to ensure that the needs of an animal for which they are responsible are met to the extent required by good practice.

12. The Welfare of Farmed Animals (England) Regulations 2007, the Welfare of Farmed Animals (Wales) Regulations 2007, and the Welfare of Farmed Animals (Scotland) Regulations 2010 make further provision for the protection of farm animals. These Regulations do not apply to farmed fish, despite a 2014 recommendation from the FAWC in their Opinion on the Welfare of Farmed Fish (paragraph 118) ‘that governments should extend the requirements for terrestrial species in the Welfare of Farmed Animals Regulations (WOFAR) to farmed fish (as appropriate and with suitable modifications)’. The WOFAR regulations for England, Wales and Scotland implemented various EU (European Union) directives (Council Directive 98/58/EC concerning the protection of animals kept for farming purposes, and species-specific EU directives for laying hens, meat chickens, pigs and calves). Schedule 1 to the three Regulations contain the following provisions, which were originally transposed from Council Directive 98/58/EC:

Breeding procedures

28.—(1) — Natural or artificial breeding or breeding procedures which cause, or are likely to cause, suffering or injury to any of the animals concerned, must not be practised.

(2) Sub-paragraph (1) does not preclude the use of natural or artificial breeding procedures that are likely to cause minimal or momentary suffering or injury or that might necessitate interventions which would not cause lasting injury.

29. Animals may only be kept for farming purposes if it can reasonably be expected, on the basis of their genotype or phenotype, that they can be kept without any detrimental effect on their health or welfare.

13. The Mutilations (Permitted Procedures) (England) Regulations 2007, the Mutilations (Permitted Procedures) (Wales) Regulations 2007, and the Prohibited Procedures on Protected Animals (Exemptions) (Scotland) Regulations 2010 specify which breeding procedures may be used in relation to cattle, pigs, birds, sheep, goats, horses, deer and other species and any relevant conditions that must be met. For instance, in England and Wales, embryo collection or transfer by a surgical method, and ovum transplantation, may only be used for cattle, sheep and goats, and – in the case of a procedure carried out as part of a conservation breeding programme – for other species. In Scotland, this procedure may also be carried out on pigs. Laparoscopic insemination can only be carried out in sheep and goats, and in England and Wales, only as part of a breed improvement program. Implantation of a subcutaneous contraceptive may not be carried out on a farmed animal, except for fish, in Scotland. Additionally, requirements such as use of anaesthetic for certain procedures are detailed.

14. The Aquatic Animal Health (England and Wales) Regulations 2009 and the Aquatic Animal Health (Scotland) Regulations 2009 regulate and enforce the prevention, control, and eradication of aquatic animal diseases to protect both farmed and wild fish and shellfish populations. They regulate the aquaculture industry and require aquaculture facilities to be authorised, implement biosecurity measures, maintain detailed records, report serious ‘notifiable’ diseases, and lay out rules for animal movements to prevent disease spread. Enforcement is conducted by the respective Fish Health Inspectorate for each country. These have the power to inspect sites, take samples, issue legal notices to restrict movements during an outbreak, and prosecute businesses for non-compliance.

15. There is further legislation governing the use of breeding techniques for cattle and the animal health rules associated with the trade of the relevant genetic material. The Bovine (Collection, Production and Transfer) Regulations 1995 specify conditions to be complied with for the collection and production of bovine embryos, including the use of anaesthetics. The Bovine Semen (England) Regulations 2007 control the collection, processing and storage of bovine semen, with comparable legislation in Wales and Scotland. There is further legislation to regulate the movement and trade of germinal products for cattle, sheep, goats, equines and pigs. The Veterinary Surgery (Epidural Anaesthesia of Bovines) Order 2010 governs the administration of anaesthesia to bovines during embryo transfer and the required conditions of those carrying out this procedure. The Veterinary Surgery (Artificial Insemination) Order 2010 permits people who are not veterinary surgeons to carry out artificial insemination of cows and mares, subject to the conditions set out in the Order. Similarly, the Veterinary Surgery (Rectal Ultrasound Scanning of Bovines) Order 2010 permits people who are not veterinary surgeons to carry out rectal ultrasound scanning of bovines, subject to the conditions set out in the Order.

16. The Animals (Scientific Procedures) Act 1986 regulates procedures that are carried out on protected animals in the UK for scientific or educational purposes that may cause pain, suffering, distress or lasting harm. The Act regulates the breeding and supply of certain species of animals for use in regulated procedures and applies to relevant modifications of a protected animal’s genes.

17. The Genetic Technology (Precision Breeding) Act 2023 provides a framework from which to build a regulatory system for precision breeding. The Act applies only in England and covers both plants and animals. Before marketing a precision bred vertebrate animal, developers would need to provide assurances in the form of an animal welfare declaration to confirm that the health and welfare of the animal and its qualifying progeny are not expected to be adversely affected by any trait resulting from precision breeding. Imported precision bred animals would also need to go through the same process as domestic precision bred animals before they could be released or marketed in England.

18. No matter where the precision bred vertebrate animal was produced, under the Genetic Technology (Precision Breeding) Act 2023, the developer would be required to make an assessment and compile data for the precision bred animal marketing authorisation in line with the regulations. This ‘animal welfare declaration’ and accompanying evidence would be subject to an independent assessment by a welfare advisory body. Secondary legislation is required to implement this regulatory framework. Until this is made, the relevant animals will continue to be regulated under the regulations for Genetically Modified Organisms.

Codes of Practice, Guidance for Welfare and Assurance schemes

Governmental Codes of Practice and Guidance for Welfare

19. In addition to the animal welfare legislation, Defra and the Devolved Administrations have produced a series of species-specific welfare codes in England and Wales, and a mixture of codes and guidance in Scotland for terrestrial livestock. These include some recommendations related to livestock breeding and decisions regarding choice of the appropriate type of animal. In England and Wales, compliance or non-compliance with a provision in a Code of Practice can be used as supporting evidence in legal proceedings for certain offences. Stock keepers are required to have access to and be familiar with the relevant code.

20. The last major updates for these codes were released by Defra in 1987 for turkeys, 2000 for sheep and 2003 for cattle, 2018 for laying hens and meat chickens and 2020 for pigs. In Scotland, the latest major issue for these codes or guidance for welfare were published in 2012 for sheep and cattle, 2019 for meat chickens and 2023 for pigs and laying hens. In Wales, the codes were published in 2010 for cattle and sheep, 2014 for pigs, 2020 for laying hens and meat chickens. There are no specific Scottish or Welsh welfare codes for turkeys.

21. There are no governmental welfare codes or guidance for welfare currently available for farmed fish, and the FAWC Opinion on the Welfare of Farmed Fish published in 2014 did not recommend creation of a statutory Welfare Code at that time. However, the recent 2025 Scottish Animal Welfare Commission (SAWC) report on Ascribing Sentience for Fish: Potential Policy Implications recommended that “Statutory Codes of Practice or Scottish Government guidance for the welfare of farmed and ornamental fish should be established, to include similar issues as for other terrestrial species, such as health, water quality, enrichment, familiarity, stocking density, pain relief, handler competence, and monitoring.” This report did not explicitly list breeding strategies and technologies within its list of topics for inclusion.

Relevant assurance schemes and industry initiatives

22. In the UK, voluntary livestock and aquaculture assurance schemes and industry initiatives often set robust standards to enhance animal welfare. These tend to focus on housing, feed, transportation and other husbandry requirements. Some schemes specify particular breeds, types of animals, breeding strategies and may prohibit or promote certain technologies. For example, the UK Better Chicken Commitment, together with the Red Tractor Enhanced Welfare scheme only permits certain breeds of chicken. Similarly, the RSPCA (Royal Society for the Prevention of Cruelty to Animals) assured meat chicken scheme requires that certain accepted breeds are used. Choice of breed may require independent assessment using the RSPCA Broiler Welfare Assessment Protocol. The Soil Association and Organic Farmers and Growers (OF&G) Organic standards require that chickens are not feed restricted, are not slaughtered before a specific age and that they produce hardy offspring of slow-growing types.

23. Other schemes focus primarily on the management and welfare of animals destined to enter the food chain. For example, the RSPCA Assured Farmed Atlantic Salmon scheme specifies how the fish should be kept and handled at different stages of their life cycle. These initiatives may not explicitly outline what breeding choices should be made. However, the production, sustainability and welfare requirements can still significantly influence the type of animal that is bred.

24. Some voluntary assurance schemes set out requirements relating to breeding practices and technologies. For instance, under the RSPCA Scheme for dairy and beef cattle, embryo transfer and ovum pick-up are not permitted except in exceptional circumstances and where there will be an outcome that is demonstrably beneficial to animal welfare.

25. Code EFABAR (European Code of Good Practice for Farm Animal Breeding and Reproduction) is a voluntary code of practice for livestock breeders. Its standards are based on a series of European Commission funded projects that facilitated collaborations between a range of stakeholders and scientists including animal breeders, bioethicists, welfare experts, economists, lawyers, and consumers. It is updated every three years (next update due in 2026). This code has been adopted by many breeding companies across Europe, including some operating in Great Britain. The Code applies to ruminants, pigs, poultry, insects, and aquaculture species. The Code emphasises the role of balanced breeding, understood as ‘a sustainable compromise for the people, the planet, and for farmed animals between traits related to the health and welfare of animals, their environmental impacts, and the quality and quantity of production, whilst keeping genetic diversity’. The six areas the Code focuses on are: animal health and welfare; environmental sustainability; genetic diversity; efficient use of resources; food and feed safety and public health; and product quality.

International context

26. Livestock production is a global industry that crosses international borders. Many of the larger breeding companies have breeding programmes in more than one country. Smaller producers may also import and export live breeding stock or cryopreserved or cooled sperm or embryos to and from other countries.

27. Animal health and welfare regulations vary significantly across countries, with some nations having stricter laws and enforcement mechanisms than others. Not only are there differences in animal health and welfare legislation, but there are also disparate levels of restriction for new techniques such as genome editing, cloning and transgenesis. Some countries are embracing biotechnology to drive innovation. For example, Brazil, Colombia, and the USA have recently approved genome edited Porcine Reproductive and Respiratory Syndrome (PRRS) resistant pigs for use in their countries’ food supply chain. Similarly, transgenic AquAdvantage Salmon have been approved (though may not be being marketed) in USA and Canada. However, other countries, particularly in the EU, remain cautious.

28. Enforcement also varies widely, with European countries and New Zealand generally having stronger enforcement while many other countries struggle with consistent and effective enforcement of animal welfare laws (Bucher et al, 2020).

29. The movement of live animals and germinal product between countries also represents a biosecurity and welfare risk.

Definitions

30. In this Opinion, key terms are used as follows:

Allele - An alternative form of a gene at a specific location on a chromosome that influences inherited traits.

Biosecurity - Measures taken to prevent the introduction of infectious agents into an environment and or stop the spread of harmful organisms between individuals.

Breed - A group of animals with defined characteristics and that are bred from within a closed gene pool.

Breed standard - A description of both the physical attributes and temperament of a pedigree breed.

Breeding (gene) pool - The different genetic variants within a breed. A small gene pool has fewer variants

Breed society - An organization that sets and maintains breed standards, registers pedigree animals, promotes a specific livestock breed, and manages its herd/flock book records.

Characteristic - An inherited physical appearance or behaviour that is associated with a breed. Synonymous with a trait.

Coefficient of inbreeding (CoI) - The degree of inbreeding. The CoI indicates the probability that two copies of a gene variant have been inherited from an ancestor that is common to both the sire and the dam. The lower the degree of inbreeding, the lower the inbreeding coefficient. The higher the percentage value, the more common ancestors there are in an animal’s pedigree.

Dominant - A form of inheritance of genes where only one copy of an altered variant of a gene needs to be inherited for the offspring to express the trait.

Dystocia - Abnormal or difficult birth. Dystocia can occur for a range of reasons including a problem with the dam, a problem with the fetus, malpositioning of the fetus or a mismatch between the size of the birth canal and the fetus. Depending on the severity of the situation, dystocias may be resolved by intervention from a stockperson or vet. In some circumstances a caesarean section or other surgical intervention may be required. In worst cases scenarios, euthanasia of either the dam or fetus may be necessary.

Epigenetics - A natural method that alters how genes are turned on or off (expressed) without affecting the DNA sequence itself. These changes can have significant consequences for both structural and functional traits including those associated with health and welfare. Epigenetic changes (modifications) provide a mechanism by which early experiences and environmental influences, both before and after birth, can have lifelong consequence. They can sometimes be passed on to offspring.

Estimated breeding values (EBVs) - A statistical prediction of an animal’s genetic merit for specific traits, calculated from performance data of the animal and its relatives and indicating its value as a parent for genetic improvement in the herd and or flock.

Genetic diversity - The variety of different genes and genetic characteristics within a livestock breed or population, essential for adaptation, disease resistance, and avoiding inbreeding problems.

Genome editing - A technology that precisely modifies DNA by adding, removing, or altering genetic material at specific locations in an organism’s genome.

Genetic index - A numerical score that combines multiple trait EBV s into a single value. This enables breeding animals to be ranked by their overall genetic merit based on breeding goals and economically important heritable traits.

Genetic potential - The maximum performance level an animal can achieve for specific traits based on its genetic makeup and under ideal environmental conditions and management. This potential may not be achieved, for example if the animal is not suited to its environment or suffered from ill-health, poor nutrition or a heavy parasite burden whilst it was young.

Genetic selection - The process of choosing animals with desirable genetic traits as parents for the next generation to improve specific characteristics in livestock populations.

Genomic analysis - The examination of an animal’s complete DNA sequence to identify genetic markers, predict breeding values, and understand traits for improved selection decisions.

Genomic DNA - The genetic material that contains all the hereditary information inherited from both parents.

Genotype - The genetic constitution of an individual.

Germinal product - Reproductive material from animals, including semen, ova and embryos that can transmit genetic information to create offspring.

Inbreeding - Occurs when offspring are produced from two closely related animals (such as siblings or parent and offspring). In some cases, this type of breeding may be repeated over several generations. Inbreeding increases the likelihood of harmful recessive genetic mutations being expressed. It is also associated with lower fertility, reduced litter sizes and survival.

Line breeding - Selective mating of related animals to preserve and concentrate desirable traits while minimizing the risks of close inbreeding. In general, line breeding uses animals that are related, but not too closely related.

Microbiome - The collective community of microorganisms (bacteria, fungi, viruses, and other microbes) that live in a specific environment for example in the rumen or intestine, on the skin and around the farm.

Methanogen - A microorganism that produces methane as a metabolic byproduct in oxygen-free environments including the rumen.

*Milt - Fish sperm or reproductive fluid.

Modes of inheritance - The manner in which a genetic trait or disorder is inherited from one generation to the next.

Monogenic - A single gene controls a genetic trait or disorder. 

Parturition - The act of giving birth, including the complete process of labour and delivery of offspring and placenta from the dam’s reproductive tract.

Penetrance - The proportion of individuals carrying a particular variant of a gene that also expresses an associated trait.

Phenotype - The observable characteristics of an individual resulting from the interactions of its genotype with the environment.

Pleiotropic - Pleiotropic genes are those in which variation can cause observable change in two or more body systems that may often appear unrelated at first.

Precision bred organism (PBO) - Defined in legislation as a plant or animal containing any stable genomic feature arising from the application of modern biotechnology that could also have arisen through traditional processes.

Precision livestock farming - A technology-driven approach using sensors, automation, and data analytics to monitor and manage individual animals.

Predicted transmitting ability (PTA) - An estimate of an animal’s genetic potential. It determines how the offspring of that animal is expected to perform for specific traits (for example, milk production or growth rate) relative to the breed average.

Primordial germ cells - The earliest precursors to sperm and egg cells. They form early in embryonic development and migrate to the gonads, where they differentiate into gametes (eggs and sperm).

Recessive - A form of inheritance of genes where two altered variants of a gene must be inherited – one from each parent – for the offspring to express the trait.

Rumen microbiome - The complex community of bacteria, protozoa, fungi, and archaea living in a ruminant’s rumen that break down plant material into nutrients that the animal can absorb.

Single nucleotide polymorphisms (SNPs) - DNA variations where a single DNA base nucleotide differs between individuals at the same genomic position. They can serve as genetic markers for traits, disease susceptibility, and breeding decisions.

Spermatogonial stem cells - Undifferentiated cells in the testes that self-renew and produce sperm throughout a male’s life via spermatogenesis.

Trait - An inherited physical appearance or behaviour that is associated with a breed. Synonymous with a characteristic.

Type - A general description of an animal based on its purpose, function, appearance and or temperament. A ‘type’ is different from a ‘breed’ as the latter is bred from within a closed gene pool, while the former does not require this restriction.

Overview of Developments since the FAWC’s 2012 report

31. Review of the academic literature since 2012 combined with discussion with industry stakeholders indicates that there have been rapid and significant changes in livestock breeding. For example, there have been more attempts to balance productivity with selecting for genetic traits that aim to improve individual animal’s health, fertility and longevity. There has also been increased focus on breeding for sustainability and reducing the environmental impact of livestock. This includes selecting for feed efficiency and low methane emitters in ruminants (see Para 65 et seq.).

32. However, while selection for individual animal health metrics has improved, there has been much less progress in selecting for specific behavioural traits which have a positive impact on an animal’s lived welfare experience (Johansen and Arnott, 2024 and Para 55 et seq.).

33. Many of the changes have been driven by societal pressures including market forces (see Para 45 et seq.). They have also been aided by a wide array of technological advances including enhancements in genomic analysis and phenotypic trait assessment (including earlier detection and alternative parameters) combined with better data collection, analysis and interpretation. Improved image collection combined with artificial intelligence is also increasing the ability to assess complex characteristics in greater detail, with higher accuracy and at an earlier stage in life before overt clinically issues arise. Examples include gait analysis in pigs and keel bone weakness in poultry (see Para 86 et seq.).

34. Other technologies that have started to be used in livestock breeding such as genome editing have the potential to improve animal health, enhance pathogen resistance, improved thermal tolerance and other fitness traits. However, it has also been reported that these genetic manipulations could result in unintended consequences especially when animals with these edits are moved into other environments (for example onto commercial farms) or bred onto different genetic backgrounds (see Para 164 et seq.). The welfare impacts of modern breeding technologies are discussed in detail below (see Para 125 et seq.).

35. As data becomes increasingly centralised and key animals are identified, there may be a loss of genetic diversity that could affect the ability of the national herd and or flock and or shoal to face future environmental challenges. These include changing weather patterns and new pathogens and parasites (see Para 71 et seq.).

36. Reproductive technologies combined with improved genomic analysis (see Para 86 et seq.) are also speeding up the rate of genetic change in livestock. For example, the genetic potential PTA of a dairy bull to enhance traits in his female offspring can now be predicted using genomics and sophisticated statistical analysis before he reaches puberty and is old enough to have viable sperm collected. Previously, it would have taken several years to collect these data (time for a bull to grow to the age where his sperm could be collected (or natural mating to occur), combined with the time required for his heifer progeny to reach their first and subsequent lactations). Any negative impact on health or welfare (for example, associated with the genetic material of the animal whose semen is being used so widely and/or the assisted reproductive procedures used to achieve pregnancies) will occur at a more accelerated pace than was previously possible.

Structure of livestock breeding industries

37. There is not a “one-size-fits-all” structure that describes the breeding strategies utilised for all species being considered within this Opinion. Instead, different approaches and techniques are employed depending on the species. This variation highlights the complexity of modern livestock breeding and the various factors – practical, economic, environmental, cultural heritage and ethical – that influence breeding decisions and determine which reproductive technologies are used. However, overall, there is a trend for these decisions to become more data driven (see Para 97 et seq.).

38. The breeding strategies of the different livestock species being covered in this report generally fall broadly into two main categories (as detailed in Para 39 et seq.). However, in reality, there is a continuum of breeding approaches across UK livestock farms, with some breeders readily adopting recent technical advances to rapidly alter their livestock’s genetics, whilst others prefer to follow a more traditional approach — relying on natural matings that use “breed standards” or their own experience, unquantified instinct or financial limitations when selecting breeding stock.

39. The vast majority of poultry (laying hens, broilers and turkeys), salmon, and pig breeding in the UK are controlled by a limited number of international companies. In contrast, the sheep breeding industry and breeding of rare breeds for all terrestrial species tend to be more fragmented, with individual farmers and or breed societies making breeding decisions based on their own context-specific requirements.

40. The cattle breeding industry falls in between these two extremes, with the dairy industry increasingly taking more centralised breeding decisions while breeding decisions for many beef suckler herds are usually still controlled by individual farmers. In addition, the origin of many cattle destined for the beef market is changing. Data from the British Cattle Movement Service (BCMS) and The Agriculture and Horticulture Development Board (AHDB) indicate 37% of prime cattle slaughtered in Great Britain (GB) in 2024 were classed as dairy-beef, up from 28% in 2019. Although producing calves destined for the beef market from dairy cattle is often considered environmentally sustainable because both meat and milk are produced from a single herd, this approach does potentially have welfare implications. For example, choice of beef sire can determine level of dystocia (problems giving birth) –see Appendix 3. In addition, dairy calves are predominantly separated from their mothers within hours or days of birth. This separation prevents maternal bonding and nursing behaviours and can increase stress for both the cow and calf. In addition, dairy-beef calves are often kept on different farms at different stages of their development. Each location change may require the calves to be transported long distances. In contrast, calves in beef suckler herds typically remain with their mothers until weaning at 6-12 months of age. This permits natural suckling and enhances herd social development, both of which may help promote their natural immunity and improve their emotional welfare.

41. The more centralised, industrial approach applied to poultry, salmon and pig breeding aims to produce uniform traits over large populations to meet specific market demand. The companies that run these breeding programmes are often large-scale conglomerates with global reach that they operate across national boundaries to distribute genetic material world-wide. They usually produce different types of animals to meet specific local requirements because these vary between countries and depend on a range of factors including environmental conditions, local cultural and societal norms, different production systems and market requirements. Breeding companies work closely with local farms to understand these requirements and adapt their breeding goals accordingly.

42. The other more fragmented approach adopted by many sheep breeders, breeders of rare terrestrial breeds and individual farmers, especially if they implement less intensive practices such as organic or low input systems, may prioritise other factors such as overall ecosystem health, sustainability or cultural heritage.

43. Animals are bred for purposes beyond just meat, milk or egg production. Traits such as disease resistance, longevity and adaptability to changing conditions and specific local environments are often valued. While some farmers focus on maintaining genetic diversity within their flocks and or herds to meet these goals, others may use line-breeding to try to “fix” particular desirable traits within their animals.

44. The UK also has over 160 native and rare breeds of terrestrial livestock (cattle, sheep, pigs, poultry, goats and equines) several of which are geographically concentrated. Some of these breeds may have rare genotypes and traits that could become increasingly relevant when meeting challenges such as climate change or developing resistance to new infectious pathogens. Thus, maintaining genetic diversity within these small populations may become important for the UK’s food security, ecological service provision and retaining our rural cultural heritage. On the other hand, if the genetic diversity reduces in these rare populations (because they are not perceived to have sufficient commercial value), then they are at increased risk of developing hereditary defects that may have welfare implications.

What drives the type of livestock produced in the UK?

45. Modern livestock and aquaculture genetics, along with current breeding strategies, are shaped, not only by an individual farm’s specific context, but also by the regulatory framework and the expectations of supermarkets and the public. These additional stakeholders have distinct, but overlapping, priorities which influence the types of animals produced and their requirements have significant implications for animal health and welfare.

46. Historically, selection strategies that focused on high productivity rates had significant health and welfare implications. To address these challenges and, as noted in the 2012 FAWC Opinion, there is a growing emphasis on balanced breeding goals that consider not only production efficiency but also animal health, welfare, and environmental sustainability (see Para 79 et seq.). Similarly, fertility sustained productivity over multiple cycles and longevity (see Para 101) is also important to farmers, especially when replacement costs for breeding stock are high.

47. Public priorities around food are complex and multi-layered, but key concerns include affordability, food security, health and nutrition, food safety and hygiene, animal welfare and environmental issues. In addition, there is growing pressure from policy makers to source products from systems that are environmentally sustainable, such as those with lower greenhouse gas emissions or reduced resource use.

48. Supermarket contracts with farmers attempt to reflect this wide range of consumer expectations. For example, they demand uniform product quality such as consistent meat cuts, egg sizes or fish fillets. Abattoirs, in particular the larger processors, prefer animals with standardised conformation and weight with calm behaviour and without horns as any variation can slow their production line, increase costs and have potential food safety or carcase contamination impacts where automated butchery may be employed. The animal product needs to have appropriate tenderness and appearance with a long shelf life. Supermarkets also aim for competitive pricing and so encourage their contractors to lower production costs.

49. Previous successful marketing strategies can also have a profound and long-lasting effect on consumer demand. For example, in the 1970s, marketing fuelled perceptions in United Kingdom (UK) consumers that brown eggs were healthier than white eggs and or that they were more likely to be produced by hens that live in free-range conditions. However, there are now breeds of white leghorn chickens (who produce white eggs) that may have a lower tendency to feather peck others and so may be easier to manage with a full beak. They also have a longer production cycle (100 weeks compared to 78 weeks, with fertility and health parameters being maintained, as the AWC understood from stakeholders with whom we interacted) and a better feed conversion ratio. This lowers the flock carbon footprint and reduces production costs (Sobolewska (2024)). Despite these possible advantages in adaptability, behaviour and sustainability associated with white leghorns, approximately 90% of eggs currently sold in the UK are still produced by brown hens. In comparison, eggs from white leghorns have now overtaken those from brown hybrids in several European countries as productions systems have swung from cage to barn or free-range systems.

50. In response to these varied demands, the majority of farmers aim to produce animals that are uniform across the herd and or flock and or shoal, convert feed more efficiently, finish at a younger age, produce higher yields of meat, milk or eggs while also showing improved fertility and increased longevity. Breeders therefore select animals with these varied “desirable” traits and that can produce offspring with similar characteristics.

51. Alternative livestock production strategies such as outdoor systems in pig and poultry farming are also being actively adopted in response to consumer demand, plus retailer and food service commitments. However, changing the animal production system can fundamentally change the trait selection priorities. For example, emphasis may shift from maximizing growth rate or egg number in controlled indoor environments to traits such as increased foraging behaviour or ability to adapt to weather fluctuations that may improve survival in more unpredictable conditions. Living in a varied terrain may also demand greater musculoskeletal strength that could offset inherent osteoporosis issues that can occur in laying hens. Similarly, there may need to be greater focus on immune competence and general disease resilience if the animals are at an increased risk of exposure to pathogens and parasites. Outdoor animals may also require different digestive efficiencies in order to utilise a varied diet that includes pasture and insects.

52. In broiler chickens, some stakeholders consider that the adoption of the use of “slower growing” strains of bird should be introduced into commercial production systems to alleviate some of the health and welfare issues which may be associated with rapid growth rates (for example metabolic, skeletal and locomotor diseases). This approach has been advocated as one of the criteria to fulfil the UK Better Chicken Commitment, in conjunction with the Red Tractor Enhanced Welfare Scheme. Industry considers it is addressing these issues with their on-going balanced breeding programmes that they continue to develop to increasingly emphasise welfare criteria for all breeds.

53. In layer chickens to avoid the routine culling of unwanted day-old male chicks, there have been calls to adopt the use of “dual purpose” breeds such that the females can produce eggs and the males, rather than being culled, could be grown on for meat production. See the AWC 2023 Opinion: ‘Alternatives to culling newly hatched chicks in the egg and poultry industry’.

54. In both situations (described in Paras 52 and 53), if meat yield and egg production were proven to be sufficiently productive and there was a suitable market model to sustain these types of production, then such approaches could become economically viable. However, progress to date in both areas has been very limited but continues to be explored.

Attitudes of stakeholders towards “health” and “welfare”

55. During the AWC’s review of the academic literature and our discussion with both industry and academic stakeholders, it rapidly became apparent that “good health” was often regarded as synonymous with “good welfare”. Good health is usually a prerequisite for good welfare as animals free from disease, injury and physiological disorders are more likely to experience positive physical and mental states. However, animal welfare extends beyond the physical condition and incorporates mental well-being, the ability to express natural behaviours and the animal’s capacity to adapt to its environment. Breeding programmes that focus exclusively on health metrics risk overlooking these broader welfare-related traits and may potentially produce animals that are less resilient to environmental challenges and are more susceptible to stress-related behaviours. However, robust, reproducible quantitative welfare and behavioural assessments are much harder (and often more expensive) than health metric assessments to develop and implement.

56. When considering terrestrial livestock, it can also be hard to identify and select for the genetic component of behaviour because results will be heavily influenced by the animal’s current environment, its previous experience and learning, its position within the flock and or herd social hierarchy and its interactions with others.

57. For salmon (and all other fish species), there is significantly less known about what drives the behaviour of individual fish. Research in this field is hampered partly because currently it is challenging to identify and monitor individuals within a shoal over time.

Conflicts between individual animal welfare and population level animal welfare and  or breeding goals

58. There are numerous examples where efforts to improve traits like growth rate, feed efficiency, productivity, disease resistance, reduction in skeletal abnormalities at the population level can negatively affect the health and welfare of individual animals within the breeding environment. Many of these unintended welfare consequences for numbers of breeding animals which are relatively small compared to the numbers of animals in the wider population which will be affected by the realisation of breeding goals are often seen by industry as necessary to evaluate the impact of genetic improvements in wider commercial environmental and management settings to assess genotypic and phenotypic progress. Some (non-exhaustive) examples include:

• Feed restriction in breeding stock where the feed meets basic nutritional requirements but is not sufficient to keep the animal fully satiated. This can result in hunger, frustration and stereotypic behaviours. For example, the breeding stock for broiler chickens and turkeys are often feed restricted to prevent them becoming overweight as this can lead to increased lameness and other skeletal issues. Likewise, breeding sows are often kept on a restricted diet to maintain an adequate body condition score (BCS) that avoids metabolic disorders and ensures productive and reproductive performance. Similarly, boars in boar studs are also not fed ad lib.

• Assessing general resilience to environmental stressors. Poultry breeding companies maintain their breeding stock in very high biosecurity facilities. In order to ensure that offspring will be resilient to commercial farm conditions, groups of birds with the same genomic profile as those being sold will be stress tested in housing conditions reflecting those found on most commercial farms. Although housing conditions do not fall below that legally permitted, environmental stressors such as stocking density, bedding cleanliness, water quality may be suboptimal and below the requirements of some assurance schemes.

• Challenge testing for disease resistance. Small groups of animals are directly exposed to disease-causing agents. In the UK, these studies would be performed under the Animal (Scientific) Procedures Act 1986. However, as livestock breeding is a global industry, some of this research may be undertaken in countries with less strict welfare regulatory frameworks.

• Assisted Reproductive Technologies facilitate propagation of desirable genetic traits from high value animals (see Para 105 et seq.). High-merit donors may be used multiple times which can reduce genetic diversity. In addition, some of these procedures can cause a number of welfare concerns for both donor and recipient. These can include risk of ovarian hyperstimulation syndrome (OHSS) from hormonal treatment; stress from repeated handling, restraint, and being put into an unfamiliar environment; risk of injury during capture, restraint, or the procedure itself; pain or discomfort both during and after the procedure; risk of infection or other complications such as bleeding which affect wellbeing following the procedure, and the potential need for the recipient to have caesarean section to correct dystocia, as well as long-term effects on reproductive health and behaviour for both donor and recipient.

• Commercial Turkeys are bred using artificial insemination to avoid injury to female hens through natural mating due to the significant size differential between sexes. Artificial insemination can reduce the overall number of large stags needed in the breeding programme due to the dilution and management of semen. However, artificial insemination does necessitate briefly catching, handling and inverting of these large stags regularly to obtain semen, and also of the hens to be manually inseminated.

• Imaging techniques and data collection. for example CT scans for ram lambs to assess total muscle, fat and bone yield can be used as part of a breeding evaluation, to identify animals with high genetic potential to produce good carcase traits. However, welfare issues may arise from the need for these animals to be sedated and restrained on their back during the imaging procedure.

• Within the salmon industry, broodstock are regularly handled for grading and assessment. This may require the fish to be anaesthetised prior to handling and to also be removed from the water for short periods of time.

59. Breeding animals may be managed in conditions that prioritise production efficiency over their overall quality of life. Some examples include

• In some breeding companies, breeding pigs and their offspring are kept without straw bedding and with minimal enrichment, the argument being that these increase the potential risk of breaching the facility biosecurity.

• Farrowing crates are still currently used within the pig breeding industry. Farrowing crates are designed primarily to reduce piglet mortality due to accidental crushing or savaging by the sow. However, this potential benefit comes at the expense of the sow’s welfare as they restrict her movement and ability to display her natural behaviour. The UK government, in its recently published Animal Welfare Strategy (2025), stated its desire to ’work with the sector to move all sows out of farrowing crates over a sustainable transition period’.

• Breeding bulls are often housed individually for their own and their handler’s safety. Reduced social contact in an animal that would naturally live in a herd, combined with the limited space and restricted exercise may cause separation anxiety, frustration, boredom and stereotypic behaviours.

One Health, One Welfare, Sustainability

60. The concept of One Health recognises that humans, animals, and planetary health are interconnected. One Welfare extends this idea to include the well-being of animals. The UN’s Food and Agricultural Organisation (FAO) defines sustainability as “meeting the needs of the present and future generations while ensuring profitability, environmental health, social and economic equity”. The current FAO definition does not explicitly mention animal welfare. Some reports suggest that there is growing acceptance that animal welfare is an inherent component of sustainability.

61. Different groups address sustainability in different ways. For example, stakeholders who follow an “industrialised livestock system” may often concentrate primarily on economic sustainability and productivity. Thus, they may focus on a) improving feed efficiency to reduce costs and environmental impact, b) increasing growth rates and yield to meet market demands, c) enhancing disease resistance to minimise losses and antibiotic use and d) optimising animals’ adaptability to various environments.

62. In contrast, farmers who take an organic, low input, or regenerative agriculture approach may prefer to use holistic assessment measures that look more comprehensively at all aspects of their farming practices and consider how these interact with each other. Their decisions will usually aim to optimise (rather than maximise) productivity, so that livestock production is not decoupled from the land.

63. In all cases, farmers aim to use and breed from the most suitable type of animal that thrives in their specific farming system. Farmers are increasingly encouraged to remove animals from their breeding stock that do not meet their key performance indicators (KPIs).

The impact of livestock on the environment

64. Livestock production can impact the environment in several ways, including (but not limited to) greenhouse gas and ammonia emissions; spread of infectious disease and parasites to wild populations; water pollution from excess nutrients and faecal material causing algae blooms; oxygen depletion and ecosystem disruption; pollution from animal medicines including synthetic hormones; antiparasitic drugs  and antibiotics; wastage from animals being discarded as unsuitable before they enter the food chain (wrong size, wrong conformation, wrong sex, morbidity and mortality); land use, and single-use plastic crates that are used to transport poultry across international borders (for biosecurity reasons). In addition, escaped farmed Atlantic salmon can interbreed with their wild relatives potentially affecting genetic diversity.

Reducing greenhouse gas emissions using genetics

65. The main greenhouse gases associated with the livestock and aquaculture industries are methane (CH4), nitrous oxide (N2O), and carbon dioxide (CO2). Genetic selection is part of a comprehensive approach that is being adopted in order to reduce these. (Other components include improved management practices, altered feed formulation, and waste handling.) Of the greenhouse gasses, CH4 and N2O emissions can be directly affected by genetic selection. While some of these selection parameters are beneficial for animal health and welfare, others may have a negative impact.

66. Healthy animals are in general more productive. Selecting animals with improved fertility and longevity, reduced lameness and mastitis, and enhanced resilience and resistance to parasites and other infections can all significantly reduce greenhouse gas emissions. Lower morbidity and mortality combined with good fertility results in more efficient use of resources, lower replacement rates and fewer animals being needed to produce the same amount of food.

67. Direct selection for faster growth rates and feed efficiency can reduce CH4 and N2O emissions per unit of food produced. It can also reduce the finite number of animals that need to be housed, fed and transported. However, selecting for extreme growth and production rates may compromise the health and welfare of the animals if not managed carefully (see Para 79 et seq.).

68. As mentioned above, genetic selection for ruminants with reduced CH4 is being investigated. Ruminants cannot digest plant fibres, instead, they rely on rumen fermentation. In this process, specialised rumen microbes break down fibrous plant materials into simpler sugars and other nutrients that the animal can absorb through its intestinal lining. This symbiotic relationship is essential for ruminant health, welfare and survival. However, hydrogen is released as a waste product during the fermentation process and this can be hazardous and even fatal if it is excessive and accumulates in the rumen. To prevent this, rumen methanogens combine hydrogen with carbon to form CH4. Ruminants then eructate (burp) this CH4 into the atmosphere to keep their rumen healthy.

69. Animals with low methane emissions when compared to a higher emitting cohort could have altered rumen anatomy, physiology or immunology. The composition of the rumen microbiome and perhaps the rumen acid-base balance may also be affected, with as yet unknown welfare consequences. It is possible that eating, resting and ruminating behaviour may be affected. Recent research from Australia assessing a range of parameters in sheep seems to indicate that more feed efficient animals spent more time eating and that this correlated with higher CH4 emissions. Other research (in cattle), however, suggests that the relationship between feed efficiency and methane outputs is complex. Current on-going projects such as the Defra-funded Breeding for Ch4nge programme in sheep that is measuring CH4 output in fully performance recorded sheep and gathering data on feed efficiency and rumen biology should provide further insights.

70. Both N20 and CH4 (and ammonia) are also released from animal excreta. Genetic variation in feed conversion efficiency and nitrogen use efficiency is a modest component that can impact the level of greenhouse gas emissions from this source. However, the most immediate and substantial influence that will reduce levels from manure will probably come from altered feed and waste management.

How animals adapt to their environment

71. Selecting the right type of animal for the right farming context is crucial because it directly impacts health, welfare, productivity and sustainability. Choosing the right type of animal that aligns with a farm’s environment, management, resources and goals increases the likelihood of better health, lower disease rates and improved welfare.

72. Livestock animals, despite domestication, retain remarkable abilities to adapt to their environment although some traits have been lost compared to their wild or rare-breed counterparts. Beef breeds like Hereford and Angus, developed in temperate climates, exhibit superior cold tolerance compared to breeds like Brahman that originated in tropical regions. Modern pig breeds that have been selected for reduced fat coverage, lean meat and large litter sizes, may have inadvertently lost some genetic adaptations that enable native-breed pigs and wild boars to forage or thermoregulate. In sheep, breeds like Merino can thrive in arid climates due to genetic adaptations that facilitate water conservation and heat tolerance. In open-water systems, Atlantic salmon are exposed to predators, parasites, and environmental changes like temperature fluctuations and algal blooms. Genetic strains of fish that have been selectively bred for rapid growth and feed efficiency may inadvertently also have reduced ability to adapt to these varying conditions as the result of the production-focused selective breeding.

Genetics X Environment (GxE) – epigenetics

73. The genetic make-up of an animal establishes its inherent potential phenotype for a wide range of characteristics including growth rate, disease resistance, behavioural tendencies and metabolic efficiency. However, environmental factors and management practices determine whether an animal will reach that genetic potential. Even animals with outstanding genetic potential will underperform in unsuitable environments. For example, a dairy cow may have the genetic potential for high milk yield but inadequate quality colostrum intake immediately after birth or poor nutrition later in life, stress or disease will limit her actual production. Conversely, thoughtful management and good stockpersonship can help animals with “average” genetics thrive.

74. Epigenetics refers to the study of heritable changes in gene expression that do not involve changes to the underlying DNA sequence. At the molecular level, epigenetics involves chemical modifications to DNA and histone proteins that regulate gene expression. These epigenetic modifications affect how genes are turned on or off in different tissues or at different stages of life without altering the animal’s genotype. They can have profound influence on an animal’s phenotype including its physical traits, its immune response and physiology plus its behaviour including how well an individual copes with stress, fear and anxiety. These epigenetic changes can be influenced by environmental and management factors, prior experience and learning plus previous health and exposure to a range of pathogens.

75. The health and nutritional status of the dam during pregnancy can also have significant impact on the epigenetic profile of their offspring. Moreover, there is some evidence from both rodents and humans that epigenetic modification to either parent’s DNA, even years prior to fertilisation, can also impact their offspring’s phenotype, sometimes for several generations.

76. Whatever farming system livestock animals are kept in, they face specific challenges that will influence how well they thrive. Indoor systems, particularly in the intensive livestock sector, often involve controlled environments with high biosecurity, comparatively limited space, and artificial lighting. These may induce epigenetic changes related to stress response, immune function, and behaviour. Outdoor systems expose animals to variable weather conditions, forage quality, and parasite exposure, potentially leading to epigenetic adaptations in foraging behaviour, disease resistance, and stress resilience.

77. Examples of the type of epigenetic mechanism described in the previous paragraph include undernutrition or overnutrition in pregnant swine impairing piglet growth.  Similarly, undernutrition during pregnancy can result in offspring that subsequently have altered growth rates, body composition, and susceptibility to metabolic diseases. In cattle, cows who are more able to cope with heat stress have a different epigenetic profile compared to cows which suffer from heat stress.

78. Climate change will exacerbate environmental challenges and disease burden. Maintaining diverse gene pools and better understanding the role of epigenetics and how it can be harnessed in livestock and aquaculture production will be important to ensure that we breed animals that are resilient to the challenges ahead.

Balanced Breeding

79. The breeding process is continuous and iterative. This means that desired traits are enhanced over subsequent generations. However, if the complete animal is not carefully considered, selective breeding can result in unintentional adverse health and welfare consequences.

80. Historically, livestock breeding tended to focus on a limited number of productive traits such as growth rate or milk yield. The unintended consequence of this was that health, fertility and behavioural traits that were not specifically selected for would not improve. Instead, these would either gradually worsen with each subsequent generation or else suddenly reach a “tipping point” where an adverse phenotype would suddenly become apparent in a relatively large percentage of the population.

81. ‘Balanced breeding’ takes a more holistic approach to animal breeding by assessing and improving multiple traits simultaneously. The aim of balanced breeding is to develop productive livestock strains that are not only well-adapted to specific local conditions but are also sufficiently robust to perform well across a range of environments and changing climatic conditions. Thus, balanced breeding still considers production traits but also selects for a range of health parameters (including disease resistance, lower incidence of lameness and mastitis, parasite resistance), appropriate behaviours and other functional traits such as fertility, ease of giving birth, longevity and environmental tolerance.

82. Balanced breeding can also lead to increased sustainability and enhanced profitability by producing animals that can convert feed more efficiently into usable products and by reducing the additional costs associated with poor fertility, animal replacement and veterinary treatment for conditions such as lameness and mastitis. There is also an increased interest in using selection to breed ruminants with lower methane emissions (see Para 65 et seq.).

83. By combining analysis of multiple traits and varying the relative importance of each trait to produce a specific index, it is possible to adjust breeding goals to meet changing needs or to include new phenotypic and genetic analytic tools (see Para 97 et seq.).

84. However, focussing on multiple traits simultaneously requires increased phenotypic and genomic data collection followed by more sophisticated analysis. Some traits may be negatively correlated with each other making it challenging to improve both simultaneously. Furthermore, some characteristics, for example behavioural assessments, can be difficult or expensive to measure quantitatively and non-subjectively. This can limit the ability for these traits to be genetically improved unless they can be correlated with specific genomic markers (see Para 89 et seq.).

85. It became clear to the AWC in gathering evidence for this Opinion that despite the commercial sector’s stated aim of breeding healthy animals through balanced breeding, many NGOs consider that the livestock industry remains too heavily focused on profit and productivity and that the negative health and welfare consequences associated with rapid growth and increased meat, eggs or milk yield per animal are still not being sufficiently addressed.

Breeding programmes and selection

86. There are many different farming systems. Breeding and selecting the right type of animal that aligns with a farm’s environment, management, resources and goals increases the likelihood of better health, lower disease rates, improved welfare while at the same time optimising productivity and sustainability.

87. Commercial breeding companies within the poultry, pig and salmon industries have their own genomic datasets and estimated breeding values (EBVs) for the animals they produce.

88. The Agriculture and Horticulture Development Board (AHDB) and the Genomic Evaluation Data System ‘Egenes’, based at the Scotland’s Rural College (SRUC), have a collaborative relationship that provides centralised national genetic evaluations for dairy cattle, beef cattle and sheep in the UK. They collect data from a variety of sources (see Para 97 et seq.). Once processed, the evaluation results are disseminated back to farmers, breed societies and commercial livestock breeding companies.

89. Genomic selection continues to revolutionise livestock breeding. It relies on obtaining data from reference populations. These are large groups of animals that have been phenotyped for traits of interest. DNA from all the individuals in this reference population is genotyped against tens of thousands of small DNA sequences called single nucleotide polymorphisms (SNPs) that are distributed across the genome of each animal in the reference population. Complex statistical models are then applied to identify correlations between the SNPs and the phenotypic traits which the animals of the reference population are exhibiting. This enables a relationship between the different SNP markers and the phenotypic traits to be determined.

90. The same set of SNPs are then probed with DNA from a young animal, thus identifying whether or not that animal has markers that correlated with the desirable phenotype. Statistical models are used to predict a breeding value for each trait in that particular animal. Animals with the best estimated breeding values for each desirable trait are then selected for breeding.

91. Since genomic analysis can be done at a young age, it reduces the time gap between generations, accelerating genetic progress. It also allows for the selection of animals for complex traits that are influenced by many genes, such as milk production, meat and wool quality, fertility, maternal traits such as ease of giving birth, offspring survivability, egg production and shell strength, reduction in keel bone fractures, and resistance to internal and external parasites. By knowing pedigrees and kinships between animals, it also enables male animals to be identified who will pass on desirable traits that are only expressed in their female relatives, for example good milk yield or good maternal instinct.

92. Genomic analysis also improves the accuracy of breeding value predictions for traits that are challenging or expensive to measure (for example longevity, disease resistance, food conversion efficiency, methane emissions) or that may traditionally require slaughter to measure (for example carcass and meat quality).

93. Genetic indices combine the estimated breeding values (EBVs) for several different traits together to give a single figure. Different indices are produced depending on the traits being analysed and by varying the weighting given for each trait. For example, the Profitable Lifetime Index for dairy cattle (PLI) emphasizes traits, including good health traits such as reduced lameness and mastitis that contribute to a cow’s lifetime profitability while the EcoFeed Genetic Index helps dairy farmers select cattle with genetic traits that contribute to improved feed efficiency and reduced environmental impact. In sheep and beef cattle, different indices are provided for animals that will produce future breeding stock (maternal traits) and terminal sires whose offspring will directly enter the food chain.

94. Although genotyping can be expensive, the overall cost is often lower than traditional methods of selection that require extensive phenotypic data collection over long periods of time. It also should eliminate the need for lengthy trials and experiments before determining the suitability of an animal for breeding. Instead, the genetic makeup of an animal can be used as a predictor for future success as a breeding animal.

95. According to its advocates, this type of advanced selection methodology means that animals with the most desirable traits can be produced more efficiently, advancing the livestock industry as a whole. However, the initial set up costs for genotyping and data analysis are high. It requires large reference populations for accurate predictions and the data from the reference populations and the statistical predictive models need to be continually updated. If not properly managed, there may be increased inbreeding and uniformity within the population. These issues concern detractors for this methodology who also question whether this centralised system can identify animals that are well adapted to thrive in specific local environments where alterations in gene expression in response to the environment (epigenetics) and the gut or rumen microbiome may play fundamental roles.

96. Breeding sales for cattle (especially beef) and sheep are still major events in the farming calendar. Prior to sales, animals may undergo invasive procedures which compromise welfare to varying extents, for example, blood testing and electroejaculation to facilitate semen analysis. In a sale situation, visual appraisal and cost are often the main selection criteria. Although dedicated pedigree bull and ram sales will publish EBVs in the catalogue, the majority of breeding animals sold through auction do not have accompanying EBVs. Many farmers travel long distances to attend these sales and therefore animals will often also undertake long journeys.

Data management

97. The sophistication of data collection and analysis plus the use of precision livestock farming technologies such as wearable sensors, Global Positioning System (GPS) and video imaging varies across the different livestock sectors. These new technologies on commercial farms enable individual animals to be monitored in group situations. This can help inform evidence-based welfare assessments. However, aquaculture in particular currently faces challenges in identifying individuals when these are kept on commercial farms.

98. Phenotypic data can be collected from a wide range of different sources including health records, milk yields, growth rates, fertility data such as age at first parturition or days between parturition, and abattoir data including carcass confirmation and condemnations.

99. The high level of biosecurity in breeding units (especially in the pig and poultry sector) means that breeding animals are not exposed to the environmental and pathogenic challenges found on many commercial farms. Therefore, breeding companies often use “monitor farms” to determine how genetically similar animals perform under environmental conditions found on commercial farms.

100. In order to make appropriate breeding decisions, phenotypic data can be combined with pedigree records and genomic data. In the poultry, pig and salmon industries, the use of this data is controlled and managed in-house by the breeding companies. In contrast, in cattle and sheep industries, AHDB and breed societies curate centralised databases and help individual farmers interpret the results.

101. As data becomes more complex, they require sophisticated software tools including artificial intelligence and machine learning to generate meaningful insights that can be actioned appropriately. However, this complexity means that single metrics that are affected by multiple other factors should not be viewed in isolation as welfare indicators. For example, longevity should not be viewed in isolation as a welfare indicator because management decisions made on grounds other than health or welfare could also affect longevity (as reflected in a higher cull rate at a younger age). In addition, when different technologies and software are used to detect and measure the same or similar characteristics, it can be challenging to directly compare and combine different datasets. This issue may be particularly important for industries where datasets are collated from independent small to medium scale farms, as is commonly the case for cattle and sheep.

102. For data collection to have a meaningful impact on animal welfare, it needs to be relevant, validated, consistently recorded and presented, robustly interpreted, regularly reviewed and used to drive improvements at the individual animal, population and data collection levels.

103. Artificial intelligence and machine learning has the potential to play an increasingly important role in animal management, phenotypic trait analysis and data collection. The full potential remains to be realised.

104. Technological advances in monitoring individuals in group situations can help to inform evidence-based welfare assessments. As noted previously (see Para 97) aquaculture currently faces particular challenges in identifying individuals.

Breeding technologies

Assisted Reproductive Technologies

105. There are a number of Assisted Reproductive Technologies used in the livestock breeding industry. These can be subdivided into gamete and embryo collection, artificial insemination and embryo transfer into a surrogate, aiding parturition (Caesarean sections), and ex-vivo procedures without or with manipulation of the genome.

106. Although there are species-specific differences, some techniques (for example artificial insemination, semen collection and freezing and embryo flushing and transfer) are widely used in mainstream livestock breeding. Their success and application vary across species (for brief details see below). General welfare considerations are often similar and they have been discussed together (see Para 123 et seq.).

Gamete and embryo collection

107. In mammals, the gametes (eggs and sperm) or embryos are usually collected from live donor animals. In salmon, donor adults are often culled just prior to the gametes being stripped. In contrast, for poultry, eggs are typically laid and do not require invasive procedures, however abdominal massage is required to collect sperm from male chickens and turkeys.

Ovum pick-up (OPU)

108. OPU is a reproductive technology used to collect oocytes (immature egg cells) directly from the ovaries of live female mammals. It is typically performed either under sedation or using local anaesthesia (depending on the species) by inserting a needle through the vaginal wall or via a laparoscopic approach into the ovarian follicles under ultrasound guidance.

109. OPU allows for the collection of oocytes from high-value females to produce multiple offspring with desirable genetic traits as it enables the production of more offspring from valuable animals than would be possible through natural breeding or embryo transfer. It can also be used to preserve genetics from rare or endangered breeds. It is most often used in both beef and dairy cattle. It is also used to a lesser extent in small ruminants and sometimes has been used in pig breeding programmes.

Sperm collection from mammals

110. Bulls, rams and boars are trained to mount a dummy or live female and semen is collected using an artificial vagina, manual stimulation or by electroejaculation. The semen is evaluated under a microscope to assess the sperm concentration, motility and morphology. It is then processed depending on the species.

111. Frozen semen is widely used and highly successful in cattle. This enables the semen from a single collection from a bull to be stored, safely transported over long distances and used over many months or even years. However, the pregnancy rates in pigs, sheep, chickens and turkeys are significantly lower with frozen semen and therefore, in these species, fresh or chilled semen is often used. This means that the logistics of storing and transporting semen long distances or across international borders are challenging. As a result, some pig breeding companies prefer to transport live stud boars instead.

Sperm and egg collection in salmon

112. Instead of allowing adult mature fish to spawn naturally in the wild or in tanks, commercial Atlantic salmon breeders manually “strip” eggs and milt (sperm). Depending on the standard operating procedure of the breeding company, this is performed either on anaesthetised live or recently killed adults. In addition, some companies anaesthetise adult fish several times whilst they check and handle them prior to collecting gametes.

113. For those female fish who are being stripped whilst anaesthetised rather than shortly after death, anaesthesia is achieved by immersing the fish in a tank containing anaesthetic solution. A stockperson then releases the eggs by a firm stroking motion along the abdomen. Some facilities introduce compressed air through a needle into the abdominal cavity of the anaesthetised fish to push out the eggs. Once stripped of her eggs, the female is put into a tank to recover.

114. Some males are killed either before or after first stripping, others are anaesthetised for milt extraction that is achieved by stroking the abdomen, and they are then allowed to recover in water for future use.

Artificial Insemination (AI)

115. Artificial insemination (AI) is a widely used reproductive technology in many livestock species, including turkeys, sheep, pigs, and cattle. It involves the collection of semen from a male and its subsequent introduction into the reproductive tract of a recipient female to achieve pregnancy. The process, health, and welfare implications vary across species, as does the need for synchronization of oestrus cycles.

116. AI in poultry is somewhat different from mammals as the females do not need to be synchronised as they lay eggs regularly. The semen is collected, diluted and typically deposited into the female’s oviduct by inserting a syringe or straw. The process is relatively quick and does not require sedation or surgical intervention, although the hen must be caught and briefly inverted during the process.

117. The disparate size of male and female commercially bred turkeys produced by previous selective breeding programmes mean that it is now considered better for bird welfare to use AI rather than natural matings for these birds.

118. In cattle and pigs, AI is normally carried out non-surgically using a catheter which is introduced through the vagina and then through the cervix so that semen can be deposited directly into the uterine lumen. In contrast, in sheep, although non-surgical, transcervical AI is possible, the semen is more commonly deposited using a surgical laparoscopic approach via the abdominal wall.

Embryo transfer

119. Suitable recipients for embryo transfer need to be in good health, lack any reproductive disorders and be compatible with the donor with respect to size of the fetus. If the embryos are not frozen, the oestrus of the donors and recipients needs to be synchronised with each other, otherwise pregnancy rates will be considerably lower (highest conception rates are achieved when the embryos are transplanted into a uterine environment that most closely resembles the environment that embryo originated from).

120. In cattle, embryos can be transferred non-surgically, trans-cervically into the uterine horn. However, trans-cervical introduction of embryos has a relatively poor success rate in pigs and sheep and therefore a laparotomy (abdominal surgery) is often used.

Multiple Ovulation and Embryo Transfer (MOET)

121. MOET is a reproductive technology used to increase the number of offspring from genetically superior mammalian females. MOET is of greater relevance for ruminant species than for pigs because of the much smaller natural litter size of ruminants. MOET is not used in poultry nor salmon.

122. The process involves hormonal treatment to superovulate a female donor animal to induce her to produce multiple eggs, and artificial insemination is used to fertilise her. In cattle the resulting embryos are collected by flushing fluid through a catheter inserted into the uterus via the cervix. However, success rates using this approach are much lower in sheep, in whom embryo collection usually requires a laparotomy (abdominal surgery). Collected embryos are evaluated under a microscope. They can either be immediately transferred to another surrogate or for sheep and cattle, where successful cryopreservation methods have been developed, they can be frozen for transportation or storage.

Welfare concerns of gamete and or embryo collection and transfer into surrogates

123. These procedures can have significant health and welfare implications for both the individual (see Para 58 and 59) and for the population as a whole.

124. Important aspects of management aimed at addressing such potential for negative welfare effects include implementing best practice, following standard operating procedures, ensuring that appropriate training is undertaken by personnel performing the procedures, and using the correct equipment and techniques. Stress should be minimised by good stockpersonship and correct handling. Veterinary oversight, correct levels of anaesthesia and sedation, pain management and post-procedure care should also be implemented.

125. Some infectious pathogens can contaminate germinal products, risking potential transmission to either the recipient or offspring and compromised welfare consequent upon poor health. Germinal products should therefore be screened for known pathogens to reduce the risk of this occurring.

126. Extensive use of a small number of genetically superior animals can narrow the gene pool over time, potentially introducing welfare-reducing undesirable traits and population vulnerabilities to diseases and environmental changes.

Parturition

127. Parturition is a term specifically used to describe the birth process in mammals. It covers the entire process of labour plus delivery of the offspring and placenta. It can present several animal health and welfare concerns that vary depending on the species, management practices, and environmental conditions.

128. Historically, genetic selection for traits that prioritised high productivity, for example large birth weight and muscularity in beef cattle and sheep can all result in problems during parturition. Many breeding strategies now specifically include selection for traits that decrease the risks associated with giving birth. These may include selecting for specific maternal traits such as ease of giving birth, good maternal behaviour, appropriate litter size, moderate frame at birth, young-stock vigour.

129. Litter size is also important as larger litter sizes can lead to increased farrowing difficulties in sows and also result in a higher incidence of still births and low birthweight piglets. Similarly in sheep, large litter sizes can increase risk of pregnancy toxaemia, dystocia (problems during birth) and lamb mortality. There are also welfare issues associated with fostering when the number of offspring exceeds the number of teats.

130. Caesarean section (C-sections) may be required to address dystocia that could either prolong suffering or endanger the life of the mother or offspring. C-sections are required more frequently in some breeds compared to others, for example in Belgian Blue cattle that carry myostatin mutations which causes an extreme muscling phenotype. C-sections, like any surgery, carry risks of post-operative pain and other adverse consequences which can have a negative impact upon welfare.

Ex-vivo procedures without genome manipulation

131. These procedures include in vitro fertilisation, genetic testing of embryo and cryopreservation of germ cells (eggs, sperm and primordial germ cells) and embryos. As these are performed outside the animal and at very early stages of development, there are few welfare concerns associated directly with the procedure themselves. However, there could be health and welfare implications to any offspring born from such procedures, and the health and welfare of the original donors and recipients also need to be considered (see Para 123 et seq.).

In vitro fertilisation (IVF)

132. IVF is a reproductive technology where oocytes collected from mammalian female donors are fertilized with sperm in a controlled laboratory setting to produce embryos. These are cultured for several days until the required pre-implantation stage of development. The embryos are then screened and either transferred  into a recipient female or frozen for cryopreservation. This procedure is increasingly used in the livestock breeding industry, especially salmon, to enhance genetic improvement, increase production efficiency, and accelerate breeding programmes from “genetically elite animals”.

133. IVF is possible in poultry. However, it is less commonly practiced and has a lower success rate compared to IVF in mammals.

134. Some in the livestock breeding industry prefer to use IVF over MOET for several reasons. These include that it is possible to collect more ova per cycle, ova can be collected from younger females, embryos can be screened for genomic traits of interest prior to implantation into the recipient surrogate and embryos can be produced with less sperm. The latter may be particularly useful for conservation purposes where the number of doses or quality of available semen is low. In addition, individual ova obtained from a single female can be fertilized with semen from different males, which can help increase biodiversity when the availability of ova is a limiting factor.

135. In addition to the health and welfare concerns relating to donors and recipients and potential reduction in the gene pool as discussed above (see Para 123 et seq.), large offspring syndrome (see Para 175 et seq.) is also more common in IVF. This can lead to difficult births and higher youngstock mortality.

136. IVF can also help limit the spread of sexually transmitted and other infectious diseases between breeding animals because it removes direct contact between animals and potentially provides an opportunity for germinal fluid to be “washed” if a pathogen were to be present in the germinal fluid. It also gives the opportunity for genetic selection for traits like disease resistance and mothering ability (see Para 137 et seq.).

Genetic testing of embryos

137. Embryo genetic testing in the livestock and aquaculture industries is an important tool for improving breeding programs, enhancing desirable traits, screening for any known genetic mutations and sexing embryos. A few cells are biopsied from embryos that have been flushed from the donor female or produced by IVF. This biopsy is usually taken at 5-7 days post fertilisation (around the blastocyst stage) in mammals, but earlier in salmon (about the 2-4 cell stage) because fish embryos develop more rapidly.

Cryopreservation

138. Cryopreservation enables genetic material from elite breeding animals with desirable traits to be stored for an extended period. This process supports ongoing genetic improvement of livestock. It can also play a significant role in breed conservation, especially for rare breeds. However, collection and storage of material is expensive, and this may exclude some small producers from making use of this technique.

139. Cryopreservation provides a backup of valuable genetics in case of disease outbreaks, disasters, or loss of important breeding animals. Breeding from frozen stores rather than live animals can reduce disease transmission risks. However, there have been reports of Bluetongue virus being transmitted from contaminated frozen bovine semen from naturally infected bulls and this may have caused a re-emergence of BTV-8 in France in 2015 (De Clercq et al.2021).

140. The cryopreservation and thawing processes can damage some cells and reduce fertility rates compared to fresh material. Pig embryos are particularly sensitive to freezing damage because of their high lipid content. Techniques such as vitrification have been used to successfully cryopreserve pig embryos. However, this is not widely practiced because of the technical challenges involved.

141. The cryopreservation of poultry also poses particular challenges. This is due to the different structure of their ovum compared with mammals, together with the poor fertility of frozen poultry semen. Whilst still under development, techniques using primordial germ cells (the precursors to gametes) holds significant promise as a way to preserve rare poultry breeds and potentially enhance commercial breeding programmes.

Sex selection and manipulation

142. In the terrestrial livestock industry, sexing semen, eggs and embryos is increasingly used to improve breeding efficiency, reduce costs, and meet market demands for specific sexes (for example, female dairy cattle, female laying hens or male broiler chickens). In the international salmon breeding industry, hormones are sometimes used to manipulate the sex of fish.

Sexed semen

143. In cattle, pigs and sheep, each sperm cell bears either an X or Y chromosome. All female ova carry an X chromosome. Fertilisation of the female’s ovum by an X-bearing chromosome results in a female embryo; fertilisation by a Y-bearing chromosome in a male embryo. As X chromosomes are much larger and have more DNA content than Y chromosomes, flow cytometry and density gradient centrifugation can separate X and Y chromosome bearing sperm based on DNA content or density differences respectively. These methods are widely used in the dairy industry to produce female calves. However, there is usually a slightly reduced conception rate due to sperm damage caused by the sorting process combined with lower sperm numbers per insemination dose. It is also possible to use these sorting methods for sheep and pig semen. However, they are less efficient in pigs due to the smaller DNA content difference between X and Y sperm in this species. They are also less common in sheep because the lower demand for this technique results in higher costs.

Sexing poultry fertile eggs and day-old chicks

144. The sex chromosome complement of birds is different from that of mammals and salmon. It is the presence of the W chromosome that determines whether a bird is female (ZW) while males contain two ZZ chromosomes. Unfertilised female eggs carry either a Z or a W chromosome. All sperm cells only bear a Z chromosome. It is therefore not possible to use the sexing semen methods described in Para 143 to select for the sex of the offspring. Instead, embryo or chick sex selection needs to be performed.

145. Currently, in the majority of hatcheries in Great Britain, newly hatched chicks and turkey poults are individually handled and examined. The sex of commercial brown layers is indicated by feather colour: females have brown feathers and males have yellow and or white feathers. Other methods that do not depend on feather colour are also in use: cloacal (or vent) sexing is frequently used for turkey poults that are bred for meat as the two sexes are usually reared separately because of their widely different growth rates. This sexing method has also sometimes been used for broiler chickens. The 2023 AWC Opinion on alternatives to culling newly hatched chicks in the egg and poultry industries provides more detail.

146. To reduce the need to cull newly hatched chicks, several new technological applications to identify or determine the sex of egg embryos are under development or in commercial use. These include amniotic fluid sampling and then using genetic markers to determine the sex of the embryo before hatching. These techniques are invasive as a small hole needs to be drilled through each eggshell. This may have an impact on hatchability and post-hatch viability of chicks. Spectroscopy and other non-invasive imaging techniques are also being investigated in both the commercial and academic sectors. Appendix 3 and the 2023 AWC Opinion on alternatives to culling newly hatched chicks in the egg and poultry industries provide more detail.

Salmon sex selection and manipulation

147. Current Atlantic salmon production mainly relies on the production of mixed sex stocks. Fisheries prefer to slaughter Atlantic salmon before they reach sexual maturity for several commercial and some welfare reasons. Sexually immature salmon devote more energy to growth rather than reproductive development. They have faster growth rates and more efficient feed conversation rates. Maintaining a stock of immature fish helps ensure a more consistent product quality throughout the year and consumers generally prefer the taste, texture and appearance of immature fish. If male salmon mature early, they can stimulate early maturation in other fish in the same enclosure through hormonal cues, affecting the entire group. Sexual maturation can be stressful for fish in captivity, potentially leading to increased susceptibility to diseases and parasites.

148. To prevent early maturation, fish farmers employ various techniques such as selective breeding for late-maturing traits, manipulating environmental factors such as photoperiod, water salinity and water temperature, and sometimes using all-female stocks to avoid male maturation issues altogether. Differential growth rates or PCR-based assays can be used to distinguish between male and female salmon during early life stages, but the latter has not been widely adopted in the commercial sector. Alternatively, a two stage process may be used where females are masculinised with hormones early in their development (so that resultant ‘neo-males’ will only carry XX sperm). These are then mated with females (also XX) to produce all female offspring which then enter the food chain. This method enables all female populations to be produced that are not themselves treated with hormones. The AWC was unable to determine whether ova produced from broodstock who have been treated with hormones in this way have been imported into UK Salmon farms.

149. From the animal health and welfare perspective, the use of hormones is intended to disrupt reproductive development. This may cause stress and can also lead to various other health issues, including increased susceptibility to diseases, abnormal growth, and developmental abnormalities. In addition, if not properly managed, there are also potential environmental impacts from hormone residues entering the water system, potentially affecting other aquatic organisms and disrupting the ecosystem.

Manipulation of the genome

150. The science of genetic improvement is fast paced, and new techniques are now being used globally both in the research community and within the commercial sector.

151. The legislative framework in the UK (and only applicable in England) distinguishes between precision breeding and genetic modification based on the nature of the genetic changes underpinning each technique. The Genetic Technology (Precision Breeding) Act 2023 distinguishes “precision-bred organisms” from genetically modified organisms (GMOs). It defines a “precision bred” organism as a plant or animal containing any stable genomic feature arising from the application of modern biotechnology that could also have arisen through traditional processes. Precision bred organisms cannot contain transgenic material (genetic sequences that could not arise through traditional breeding practices). The Act also creates a new regulatory framework for these precision-bred organisms. (see Para 17-18). However, as explained in the legal context section (Para 18), secondary legislation is required before the Act can come into force for animals in England.

152. While precision breeding could be used to improve animal health and welfare, there are concerns that it could also contribute to the intensification of animal agriculture and aquaculture and poorer living conditions which in themselves would be detrimental to animal welfare. In the view of the AWC, this is a general concern which applies not only to precision breeding but equally well to all types of livestock and aquaculture farming, and is regulated by Animal Welfare legislation other than the Genetic Technology (Precision Breeding) Act 2023, and through the associated codes of practice for the welfare of the different species (see Para 19 et seq.).

Gene Editing

153. ‘Precision bred’ animals may be produced using genome editing. Gene editing systems target a precise location within the genome and then cut or nick the DNA at that site. Identifying potential gene targets to edit and determining the complete function of that gene throughout an animal’s life is time-consuming and expensive. Whilst complete genome sequences for the major livestock species are known, the functional understanding lags significantly behind. The functional roles for the majority of genes in livestock have been inferred via homology (comparison to well-studied genes in humans or mice) and this limits their accuracy. Furthermore, most gene products are expressed in more than one tissue and may play different roles in different circumstances. Currently the tissue-specific roles, gene-environment interactions, and epigenetic mechanisms for many genes remain largely unresolved.

154. In genetic editing, researchers use the natural cellular processes required to repair the cut DNA to introduce a specific alteration. Key techniques include:

• CRISPR-Cas: This is currently the most widely used gene-editing tool. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a natural defence mechanism found in bacteria. When combined with a Cas enzyme (most commonly Cas9 enzyme), it can be programmed to target specific DNA sequences and make cuts. The choice of Cas protein depends on the specific application needs, the target type (DNA versus RNA), the desired edit type, delivery constraints and specificity requirements.

• TALENs (Transcription Activator-Like Effector Nucleases): These are proteins that can be engineered to bind to specific DNA sequences and then cut the DNA at that location.

• Zinc Finger Nucleases (ZFNs): These are another class of engineered proteins that can bind to specific DNA sequences and introduce cuts.

155. In addition to the DNA modification process itself, genome editing often requires additional assisted reproduction techniques depending on the species to provide genetic material. These can include superovulation and egg collection, in vitro fertilisation, embryo transfer, the use of surrogate dams (for mammals), (see Para 107 et seq.) and possibly, somatic cell nuclear transfer (SCNT) (see Para 175 et seq.).

156. The advantage of using SCNT in combination with gene-editing is that the cell line can be screened before the edited nuclear material is transferred into an enucleated oocyte to ensure that the desired edits, and no off-target edits, have occurred properly. However, SCNT derived offspring can have significant health issues as a result of the SCNT procedure itself (see Para 175 et seq.).

157. Micro-injection of the genome editing components directly into an in vitro fertilised one cell embryo or into an oocyte that is then subsequently fertilised would enable the editing process to occur directly within the embryo or oocyte. This would remove the need to use SCNT and overcome the health issues described in Para 177. However, although it is possible to screen developing salmon embryos prior to hatching as they develop outside the dam and without an opaque shell, this is much more challenging for mammals and poultry embryos. It will be necessary to improve the efficiency and accuracy of genome editing technology before micro-injection of the genome editing components directly into oocytes or one cell embryos becomes the preferred method of choice for terrestrial livestock species.

158. Micro-injection of the genome editing components into oocytes can also result in mosaicism. This is where one organism is composed of cells which have two or more different genotypes. It can occur when the genome edit does not occur until after the zygote has divided into its daughter cells and so only one of the daughter cells is targeted. This can mean that the phenotype observed in the founder population can be different from that of subsequent generations. Also, if the proper genome edit is not present in the germ cells, then the founders will not transmit the genetic alteration to their offspring.

Welfare impacts of genome editing

159. In principle, genome editing in livestock animals could offer significant potential advantages for the livestock industry, such as improving animal health and disease resistance, improving an animal’s ability to adapt to climate change, and enhancing productivity and sustainability. Genome editing could reduce suffering and the need for culling or costly medical treatments. However, off-target events (Para 160 et seq.), unintended secondary phenotypic consequences (Para 162 et seq.), and the possibility of facilitating new pathogen mutations if the conventional host-pathogen interaction is disrupted (Para 171) may adversely affect animal health and welfare.

160. Off-target events are unintended genetic changes that occur at locations other than the intended DNA target site. These can occur either because (a) the technology produces complex DNA rearrangements at or near the gene target site or (b) the short DNA sequence used to target the genome editing tool to a particular gene was not sufficiently specific, resulting in more than one part of the genome being edited. Off-target effects can lead to mutations, deletions, or insertions in unintended regions of the genome, potentially disrupting the expression or function of other non-target genes. These can be detected through whole-genome sequencing or specific assays designed to identify these unintended modifications.

161. Understanding and minimizing off-target events are crucial for improving the precision and safety of genome editing technologies. Proponents of genome editing argue that progress has been made with the precision and efficiency of genome editing over the past few years and believe that this trend of improvements will continue. Careful selection of a unique stretch of target DNA sequence helps to minimise off-target effects. In addition, a number of online software tools are available to perform in silico predictions of potential off-target sites based on sequence homology with the target site. However, currently these tools do not take the epigenetic status of a gene locus into account, which is important in determining the actual activity at both on-target and off-target sites. The AWC understood from stakeholders that researchers recognise that this is a priority for ongoing research, which they are trying to address.

162. Secondary phenotypic consequences are direct or indirect downstream effects of the intended edit itself. Secondary phenotypic consequences arise because the edited gene may play multiple roles in different organs of the body and the edited gene may affect the expression of other genes or biochemical pathways through regulatory interactions. If the gene function and pathways are completely understood then it should be possible to predict these secondary consequences. However, as described above (see Para 153), the complete function for the majority of livestock genes remains unresolved, therefore the genome edit could reveal previously unknown roles or interactions of the targeted gene. It should be noted that spontaneous naturally occurring mutations can also have unexpected secondary phenotypic consequences because, as already explained, the complete function of all genes is not known.

163. Furthermore, because of the interactive nature of genetic pathways in the body, the unintended impacts of a genome edit (or natural mutation) on an animal’s health and welfare may only become apparent as the animal ages, or when it is put in a different environment or management conditions or when the genome edit is introduced into a different genetic background.

Current and likely future interest in the use of genome editing in livestock breeding

164. The AWC’s discussions with industry stakeholders suggest that the demand and utilisation of this technology may be different for the different species. Thus, once the technology is proven commercially, the pig and cattle sectors have indicated that they may consider embracing its use and breed genome edited alleles into their populations. In contrast, the poultry industry representatives felt that individual genome edited strains could disrupt and significantly impact their current long-term breeding strategies and favoured improving balanced breeding through more “traditional” genomic selection utilising modern or novel selection and analytical tools.

165. Currently, several examples of genome editing in livestock have focused on improving animal health and welfare. These include producing porcine reproductive and respiratory syndrome virus (PRRSV) resistant pigs, classical swine fever (CSF) virus resistant pigs, tuberculosis resistance in cattle, the introduction of the hornless (polled) allele from black Angus cattle into Holstein-Friesian dairy cows, the production of SLICK cattle that may have better heat tolerance, plus attempts to produce chickens that are resistant to Avian Influenza. There is also interest in using genome editing to produce sterile males that can subsequently be used as surrogate sires to speed up the propagation of genomes from high value donors (see Para 181 et seq.).

166. Porcine Reproductive and Respiratory Syndrome (PRRS) is a devastating highly infectious viral disease in pigs that results in abortions, fetal and piglet death, lung disease and poor growth rates. The PRRS pathogen (PRRSV) enters and infects macrophages (a type of white blood cell that kills microorganisms, removes dead cells and stimulates other immune system cells) through the cell receptor CD163. This receptor plays several key roles in the immune system including macrophage activation, tissue repair, iron homeostasis and preventing oxidative damage from free haemoglobin in the bloodstream and modulation of the immune system to prevent excessive inflammation. Different research groups have used genome editing approaches to target CD163. For example, one group removed the whole gene (Whitworth et al., 2016), whilst another only removed the Scavenger Receptor Cysteine-Rich Domain 5 (Burkard et al., 2017). This small portion of CD163 has had no other specific role associated with it other than in PRRSV infection and its removal does not seem to affect the other functions of CD163. Both groups demonstrated that the resultant pigs were resistant to PPRSV infection and both have claimed that under laboratory conditions both types of genome edited pigs do not have any unintended health consequences. However, the approach taken by Burkard and co-workers that removes the smallest gene fragment possible appears preferable given the multiple functions of CD163.

167. Removal of horns in cattle by disbudding calves or dehorning older animals    is legally permitted in England, Wales and Scotland. However, these procedures are painful and have significant welfare implications. Horns are inherited as an autosomal recessive trait and some cattle breeds are naturally polled (lack horns). While conventional breeding could be used to introduce the polled phenotype into the unpolled breeds, there is evidence that indicates that this approach significantly slows the rate of genetic gain (reviewed in Mueller et al., 2021). Therefore, to remove the welfare harms associated with disbudding and dehorning, several research groups have used genome editing to introduce the naturally occurring polled mutation (which causes hornlessness) into high genetic merit dairy cattle breeds that are typically horned.

168. The “SLICK” trait is associated with a dominant gene mutation that results in a shorter hair coat and better heat tolerance. Several breeds of cattle in South America possess a natural mutation in the PRLR (Prolactin Receptor) that causes this phenotype. Researchers have used CRISPR and or Cas9 technology to introduce the SLICK mutation into Angus and Jersey cattle – breeds that are usually sensitive to higher temperatures (Cuellar et al., 2024). The genome edited animals showed better thermoregulation and by 469 days of age were heavier with carcase traits that were similar or better than the non-SLICK control animals. These increased weights may have been secondary to the improved thermoregulation, or they could have been caused by altered Prolactin Receptor function in other tissues. It is known that PRLR plays a role in reproduction and lactation, metabolic processes which could affect growth rates or feed efficiency, the immune system as well as influencing behaviour including maternal care and the ability to cope with stress.

169. There is also interest in using genome editing to increase meat yield andor quality. “Double Muscling” or muscular hypertrophy is a natural trait found in a range of different cattle and sheep breeds. It is often associated with mutations in Myostatin (MSTN). These animals often have a higher lean meat yield. However, it is also linked to negative welfare traits such as reduced fertility, dystocia, reduced calf survival, reduced internal organ size, increased insulin resistance and an increased predisposition to alveolar hypoxia (reviewed in Fiems, 2012).

170. In pigs, there are comparatively few natural MSTN mutations. Reports from several different research groups who have attempted MSTN genome edits in Western Pig breeds including the Large White describe congenital hindlimb weakness in newborn piglets. However, no such weakness was reported by editing this gene in two Chinese pig breeds. To investigate this further, one group produced genome edits in the MTSTN genes of Chinese high-fat Meisham pigs and Western commercial high-lean Large White pigs. All the genome edited offspring from Large White pigs which were homozygous for the genome edited MTSN allele showed hindlimb weakness and only survived for 1–2 days. In contrast, all of the genome edited MSTN-/- Meisham pigs (N=216; five generations) had normal posture and mobility. This work highlights that genome edits may have profoundly different effects depending on the genetic background. This is an important consideration not just when producing the original genome edited founders, but also in later crossbreeding decisions.

171. Avian influenza, particularly some highly pathogenic H5N1 strains, has, in recent years, resulted in unprecedented disease and mortality in poultry across the world, including in the UK. Control to date depends on strict biosecurity and statutory housing orders, with ongoing debate on the role of vaccination. Idoka-Akoh et al (2023) gene edited the chicken protein ANP32A that the Avian Influenza virus normally co-opts from its host to support its own replication. They found that 9/10 gene edited chickens remained uninfected when challenged with a low dose of low pathogenic avian influenza H9N2-UDL virus. However, when they exposed 2 week old chicks to higher titres of the same virus, there were breakthrough infections but at a lower rate than in the control chickens. Further analysis of these infected gene edited birds indicated that they were carrying a mutated form of the H9N2 virus. These new viral mutations bypassed the host ANP32A protein and instead co-opted alternative ANP32 family members. The researchers demonstrated using cultured chicken cell lines that targeting three ANP32 related genes in the same cells eliminated all viral growth. This research raises two separate animal welfare concerns. First, whether gene editing that disrupts the normal virus-host interaction facilitates novel viral mutations that could produce variants that are more contagious or more pathogenic than the original (influenza viruses are known to mutate rapidly). Secondly, there is currently no published data that demonstrates that chickens which have been gene edited to disrupt three ANP32 related genes (as performed in chicken cell lines) have health or welfare issues – or are even viable. These findings confirm the importance of a robust genome editing strategy. They also demonstrate the need to have appraisal systems that rule out any potential adverse consequences that could arise from unintentionally facilitating adaptive viral evolution.

172. The production of sterile male or female livestock for different species potentially offers several benefits to the livestock industry, including improved control over breeding including producing surrogate sires (see Para 184 et seq.), enhanced growth and productivity, better meat quality, reduced aggression, and protection of the environment and wild populations. Importantly, there may be some circumstances where it would also improve animal welfare, for example by negating any need for castration – either for management reasons or to remove the risk of producing meat with “boar taint” (pigs) or “ram taint” (sheep) from males that will not reach slaughter weight before sexual maturity.

173. Sterile salmon are often wanted by the aquaculture industry as this prevents escaped farmed fish from breeding with wild populations and thereby protects the genetic makeup of wild fish populations. Internationally,  this is currently often done by producing triploid salmon (see Para 180 et seq.).

174. Often in agriculture a single sex is preferred with the other potentially being considered surplus to requirements. Researchers working in mice have developed a strategy mediated by CRISPR/Cas9 genome editing that produces male- or female- only litters  They claim that this approach could be modified for different livestock species such as poultry and by so doing remove excess males (and the need to cull them) from production.

Somatic cell nuclear transfer (SCNT).

175. SCNT (commonly known as “cloning”) takes the genetic material from a somatic (non-germ) cell (for example a skin cell) and places it into an enucleated oocyte that has either been harvested from a live donor or obtained from abattoir material. The oocyte is then stimulated to divide by either electric shock or chemical treatment. The cultured somatic cells are either derived from high value donor animals or else have been genome edited.

176. Although significant progress has been made since the first cloned mammal, Dolly the sheep, was born in 1996, the overall efficiency of producing viable offspring using this technique remains low in most species and is, often below 10%. Embryonic and early fetal death are more frequent in pregnancies generated with cloned embryos.

177. The offspring who do survive to term sometimes exhibit a range of abnormalities and health problems, these issues stem from the complex process of cloning and incorrect gene expression that occurs due to faulty epigenetic reprogramming. Some of the common abnormalities and health problems observed include increased birth size that can result in associated dystocia, organ defects particularly in the heart, lungs and liver, immune system dysfunction, respiratory and circulatory problems, metabolic disorders, reduced fertility, musculoskeletal malformations and neurological and behavioural abnormalities. The severity and frequency of these abnormalities can vary depending on the species being cloned and the specific SCNT technique used. As SCNT technology has improved, some of these issues have become less prevalent, but the process remains complex and imperfect.

Transgenesis

178. Transgenesis is the process of introducing a gene or gene expression control elements from one organism into another to confer a specific trait. Commercially produced transgenic animals are currently not marketed in the UK. Other countries, such as the US and Canada, have established frameworks for assessing genetically modified animals. One example is AquAdvantage Salmon from AquaBounty Technologies: – it was approved by the U.S. Food and Drug Administration (FDA) in 2015 and by Canada in 2016. This is the first genetically modified animal approved for human consumption.  However, a subsequent legal ruling required the FDA to reassess this approval because they had not fully considered the consequences to the wild salmon population if any transgenic fish escaped. Furthermore, the AWC were unable to ascertain whether products from these fish have entered the human food chain.

179. This transgenic Atlantic salmon contains a growth hormone gene from the Chinook salmon and a promoter from the Ocean pout, which allows it to grow to market size significantly faster than non-transgenic salmon. The AWC are unable to comment on the welfare consequences of this transgene as we have not been able to find any peer-reviewed scientific literature that describes the health and welfare of these fish compared to non-transgenic control animals.

Triploid salmon

180. Triploid salmon are sterile because they have three sets of chromosomes instead of the usual two. They are bred by treating salmon eggs with heat or hydrostatic pressure shortly after fertilisation. This disrupts the normal movement of chromosomes during meiosis and so creates the third set. Triploid salmon may be used in aquaculture internationally for both productivity reasons and to prevent interbreeding with wild populations if they escape, thus protecting the wild salmon genetic pool from being altered by escaped farm fish. The AWC understood from our interactions with stakeholders that there are not currently triploid salmon in the UK. The RSPCA welfare standards for farmed Atlantic salmon (and hence RSPCA Assured) do not permit use of triploid salmon.

181. Triploid animals have enhanced growth rates and can grow larger and faster than diploid salmon. This is because they do not develop reproductive organs and energy is not diverted towards sexual maturation. This inability to mature sexually also stops any seasonal variation in flesh quality and enables fish farmers to produce a more consistent product year-round.

182. Triploid salmon suffer from a range of health and welfare problems and have lower survival rates than diploid fish especially during early life stages and in suboptimal conditions. They are more prone to skeletal abnormalities, particularly in the lower jaw and vertebrae. This can affect their ability to feed and swim properly. Some studies have shown that triploid salmon may have reduced heart function and aerobic capacity compared to diploid fish. They also have increased susceptibility to cataracts which can impair vision and affect feeding behaviour. In addition, they may have reduced disease resistance and increased sensitivity to environmental stresses such as changes in temperature or oxygen levels. Some studies suggest that triploid salmon may have altered feeding patterns or reduced aggression when compared to diploid fish. These behavioural differences may also affect their ability to thrive.

183. The severity of the different phenotypes observed in triploid salmon can vary depending on the specific strain of salmon plus the local environmental conditions and management practices. Because of this variability, many of the health and welfare problems currently associated with the technology could perhaps be addressed in future through ongoing research and selective breeding programmes.

Surrogate Sires

184. Surrogate sires are male animals that are initially sterile, but then experimentally induced to produce sperm containing the genetic material of elite donor animals rather than their own. They are being developed within the research community and are currently not yet in use within the commercial sector. The goal of using surrogate sires is to accelerate genetic improvement in livestock populations by propagating superior genomes from these elite donor animals more efficiently. High-quality donor animals with desirable traits such as disease resistance, high milk yield, fast growth are selected based on genetic testing and performance records. Spermatogonial stem cells (SSCs) are isolated from these donors.

185. Surrogate males are created by genome editing specific genes that are crucial for male fertility. The resultant animals are sterile but still retain he ability to produce sperm. Researchers then transplant the donor SSCs into the testes of the surrogate sterile male. Once the donor’s SSCs colonise the testes, the surrogate will produce sperm carrying the donor’s genetic material. These animals are then used to mate with females in the broader population. Using this method, multiple surrogates can produce sperm carrying a single donor’s genetic material. Because each surrogate male can mate with many females, a large number of offspring will quickly inherit the desirable traits of the single genetically elite donor.

Stockpersonship

186. Good stockpersonship, training, and staff retention are critical for provision of high standards of animal health and welfare in the livestock and aquaculture breeding industries.

187. Good stockpersonship requires empathy and the ability to handle animals in a calm and compassionate, humane manner. It also requires keen observational skills: the ability to recognise signs of health, illness and distress plus an understanding of normal and abnormal animal behaviour. Experienced managers and well-trained staff with strong stockpersonship skills can identify and address health issues early, minimise stress experienced by animals, and promote overall well-being.

188. Proper training ensures that everyone associated with the animals does so in a consistent fashion. It empowers staff to uphold high standards and respond effectively in all situations. However, ongoing continuous assessment is also required to avoid stock-person complacency andor an unintended and unnoticed gradual decline in standards (so-called “shifting baseline syndrome”).

189. Retaining experienced staff along with adopting standard operating procedures (SOPs) ensures consistency in animal care practice. Furthermore, these people possess valuable knowledge about individual animals, breeding lines, and farm-specific practices as well as the appropriate husbandry. Retaining these staff members helps maintain this knowledge within the organization, facilitating better decision-making and problem-solving. In contrast, high staff turnover can lead to inconsistencies in care routines, increased stress for animals, and a higher risk of errors or oversights.

190. Good stockpersonship and consistent care practices can lower animal stress and positively impact animal performance, such as growth rates, feed efficiency, and reproductive success. This, in turn, contributes to the overall profitability and sustainability of the business.

191. The rapid advances in Artificial Intelligence, imaging and use of sensors, data collection and analysis could both aid or hinder good stockpersonship. ‘Wearable tech’ already enables early detection of changes in physiological parameters before an animal becomes overtly ill. Artificial intelligence may also have a future role to play in detecting subtle signs of disease before they become apparent to humans. Precision Management (that is , data and technology) may be used to tailor optimal feeding strategies, environmental conditions and breeding programmes to the individual, thus improving animal welfare. Imaging techniques and automated monitoring could reduce the need for stressful handling practices (including those that may require sedation). Examples of imaging techniques and automated monitoring include imaging and machine learning for posture, gait and behavioural analysis; thermal imaging to detect early signs of mastitis, fever, inflammation or injury, and multispectral analysis for early detection of sea lice in salmon. However, over-reliance on technology could lead to a decline in essential stockpersonship skills and inaccurate or misinterpreted results could lead to poor decisions that negatively impact animal welfare.

192. As some technologies reduce the need for animal handling, they may also decrease direct interaction time between people and animals, potentially hindering the development of the human-animal bond that is essential for good stockpersonship. Therefore, in order to ensure the highest possible standards of animal health and welfare, it is key to integrate technology in a way that enhances and compliments good stockpersonship.

Ethical analysis

193. In line with its previous work and Opinions, the ethical approach which AWC has adopted in considering this issue is a primarily utilitarian one in which the human use of animals is considered permissible to achieve important benefits, providing that animal welfare is safeguarded as far as possible and, as a minimum, in accordance with national and, where relevant, international legislation. The utilitarian approach adopted by AWC is qualified in that the justification of harms is considered in relation to both the magnitude and importance of the benefits that accrue, within the context and situation under consideration. AWC recognises that there are some harms which, due to their severity, should not be inflicted upon animals under normal circumstances. Animal welfare should be maximised as far as possible in each and every situation to ensure that animals have ‘lives worth living’ and ideally ‘good lives’.

194. In the course of preparing this Opinion, the AWC often found that the evidence and data presented to us by stakeholders frequently focused primarily on health impacts rather than providing us with the broader welfare implications. This has made it difficult to undertake a detailed ethical analysis of the various breeding practices and breeding technologies within the scope of this Opinion.

195. Notwithstanding that limitation, the AWC is able to conclude that breeding practices and breeding technologies can both offer (potential) welfare benefits and cause (potential) welfare harms, as outlined within the main body of this Opinion.

196. Such welfare benefits and welfare harms may apply to female and  or male animals, and to animals currently being used for breeding and  or to future generations.

197. Ethical breeding practices and the ethical use of breeding technologies require minimisation of negative and maximisation of positive welfare impacts on animals of all genders, across current and future generations.

198. Where precision breeding techniques are being investigated, consideration of the heritability of any manipulation of the genome and associated welfare consequences (including those related to ‘off target’ effects) is necessary to fulfil these requirements.

199. Careful recording of data of both the health and welfare of male and female breeding animals and their offspring across subsequent generations, combined with objective, independent analysis, is a prerequisite for such an ethical approach (Para 193) to breeding practices and the use of breeding technologies.

Conclusions

200. The AWC recognises that since the publication of the 2012 FAWC report on this topic there have been a number of improvements and developments in breeding practices, including an increased awareness and implementation of practices related to more holistic balanced breeding.

201. The literature review which underpinned this opinion and discussion with industry stakeholders demonstrated significant knowledge gaps, including welfare assessment related to breeding, with a particular lack of evidence relating to behaviour and affective state (emotional state).

202. Industry stakeholders tend not to publish their data in peer-reviewed scientific journals.

Conclusions on legislative framework

203. Livestock production is a global industry. There is a lack of alignment in  legislation across different jurisdictions relating to breeding livestock and in particular to the use of new breeding technologies. Companies may choose to undertake the research and production of livestock produced both by traditional breeding methods and using new technologies (for example in genome editing) in countries with fewer welfare regulations and lower levels of enforcement.

204. The Genetic Technology (Precision Breeding) Act 2023 applies only to England. This may lead to issues with data collection and traceability across national and international borders.

205. The welfare codes for many livestock species are out-of-date and do not reflect the animal welfare needs associated with current breeding strategies and modern breeding technologies.

Conclusions on the welfare impact relating to the structure of livestock breeding

206. The diverse ways in which livestock breeding is structured in and between species means that welfare impacts are also diverse and cannot always  be extrapolated within or across sectors. The welfare challenges faced by breeding animals and production animals are not always the same.

207. Whatever the structure and whatever the species, all stakeholders, not just farmers and breeding companies, should share responsibility for delivering animal-centred welfare outcomes.

208. When considering welfare at a population level, it is important not to lose sight of the welfare needs of individual animals.

209. Although they make up a smaller proportion of the breeding population compared to females, the welfare of male animals should be given equal regard.

Conclusions on one health one welfare and sustainability

210. The majority of current definitions of the term “sustainability” fail to explicitly include any animal welfare considerations.

211. The current spotlight on climate change as a focus of sustainability risks causing negative consequences for animal welfare as many recommendations to reduce livestock emissions advocate production of fast growing and or high yielding animals. The AWC is concerned that focusing on this single metric (climate change) could adversely skew balanced breeding programmes.

212. The AWC is particularly concerned about the current focus on using breeding strategies to reduce methane emissions as this may alter rumen function and unintentionally impact animal health, welfare and behaviour.

213. Different stakeholders have differing opinions on the welfare advantages and disadvantages of fast versus slow growing breeds across species. Regardless, in the opinion of the AWC, it is important for animal welfare that the management system meets the needs of the type of animal.

214. The roles that the environment and different microbiomes play in modifying gene expression and function in livestock species are still poorly understood.

Conclusions on breeding programmes and selection

215. Breeding strategies are underpinned by the need for accurate phenotyping. Genomic assessment alone is not sufficient to determine good animal welfare outcomes.

216. Selecting for particular traits may increase the risk of negative welfare effects associated with existing and emerging diseases.

217. Advances in genomic analysis are rapidly speeding up genetic change within species and populations. This offers scope for beneficial change with positive impacts upon animal welfare. However, adverse unintended welfare consequences could be rapidly disseminated both nationally and internationally. There appears to be a current lack of assessment or analysis of such unintended consequences.

218. There are biosecurity risks associated with the movement of live animals and use of germinal products.

Conclusions on data collection and analysis

219. There is a vast amount of data relating to livestock breeding being collected by disparate stakeholders.

220. Poor health will cause poor welfare. However, health data alone will often be insufficient to determine an animal’s welfare status because they do not include crucial indicators associated with that animal’s behavioural needs, emotional state and the ability to express natural behaviours.

221. The AWC acknowledges that in order to optimise population-level animal welfare, it is sometimes necessary for industry to assess the performance of individual animals from a breeding programme under challenging conditions, for example using ‘monitor farms’. For this to be acceptable in a utilitarian ethical analysis, where monitor farms are used their standards should, as a minimum, comply with relevant national animal welfare legislation and supporting codes, which need to reflect animal welfare needs associated with current breeding strategies and modern breeding technologies (paragraph 205).

222. Technical advances in monitoring individuals in group settings combined with artificial intelligence have the potential to play an increasingly important role in animal welfare assessment. Such systems will require verification, and the full potential of these approaches remains to be realised.

Conclusions on breeding technologies

223. All modern breeding technologies have the potential for positive and negative welfare impacts. The significance of these impacts will vary across species.

224. There is a lack of research on the welfare impact of modern breeding technologies and stakeholders may have become habituated to the possible welfare harms to the individual animal. This issue was raised in the FAWC 2012 report and has not been fully addressed. Since that time, new technologies have also been developed for which there is also a lack of evidence regarding their impact on welfare, for example the welfare implications of transgenesis in fish.

225. The complete function of most genes and how they interact with other gene products and the environment are still poorly understood. Therefore, identifying appropriate targets to edit and predicting the effects of editing them may be difficult. This failure to understand the complete function of genes increases the risk of unintended consequences especially when the genome edit is bred onto a different genetic background or the animals are kept in different environments.

226. The Precision-Breeding Act only applies in England. This may make it difficult to gather data on the welfare of precision-bred animals across borders, including those between the devolved nations of the U.K.

Conclusions on the welfare impacts of stockpersonship

227. Animal welfare is highly dependent on the standards of care and trained, experienced, empathic stockpersons are required to maintain these standards.

228. Stockpersonship will become increasingly informed by precision livestock technologies.

229. Stockperson training and on-going assessment are critical for the protection of animal welfare of breeding animals this should include up-to-date knowledge of relevant precision livestock technologies.

Recommendations

230. Industry and government should collaborate to make grant funding available for research into the welfare impacts of breeding and breeding technologies, with a particular focus on behaviour and affective (emotional) state.

231. The AWC encourages industry stakeholders to disseminate and publish the findings of their research into the welfare impacts of breeding.

232. Following on from recommendation 111 in the FAWC 2012 report, the AWC should maintain oversight of livestock breeding and breeding technologies through frequent review. Because of the rapid development of new methods, the AWC should update this opinion at least every 5 years. The scope of breeding practices and breeding technologies is so rapidly enlarging that future updates may be best undertaken on a species-specific basis, with each and all species being reviewed at least every 5 years.

Recommendations on legislative framework

233. The welfare codes for the different livestock species need to be reviewed and updated so that they reflect current breeding strategies and include new breeding technologies. Such updates should take account of the welfare of breeding animals and their offspring.

234. Governments across the U.K. should take due account of the welfare needs of breeding animals and their offspring as part of their pre-legislative assessments of forthcoming Acts, statutory instruments and  or regulations pertaining to animal breeding. In so far as its remit allows, the Animal Sentience Committee should give its opinion on whether Government has appropriately identified & considered welfare impacts within the decision-making processes around policy relating to livestock breeding.

235. The Government should ensure that robust tracing methods are in place for precision bred animals no matter whether the animals have been produced in the UK or abroad.

236. Legislation should be enacted to safeguard the welfare of fish in aquaculture systems, for example through extension of the Welfare of Farmed Animals Regulations.

237. Welfare codes should be developed for fish kept in aquaculture systems

Recommendations on the welfare impact relating to the structure of livestock breeding

238. Welfare assessments should appraise individual animals. They should be tailored to the species, system, age and or stage and sex of the animal.

239. There should be an onus on all industry stakeholders to be informed on the concept of animal welfare as set out in the five domains model of animal welfare, and particularly to distinguish between health and welfare. This should be reflected by appropriate regulatory oversight, for example through updating the welfare codes.

240. Industry and Academia should be encouraged to develop practical, cost-effective, robust, reliable and reproducible methods of assessing animal welfare including appraisal of the emotional state of the animal effectively both on farm and within livestock breeding facilities. This should be supported by government.

Recommendations on one health, one welfare and sustainability

241. Definitions of sustainability should always incorporate a consideration of animal welfare. Similarly, sustainability assessments should include metrics that assess animal welfare.

242. Government and industry should collaborate to fund research on the short- and long-term welfare consequences of current goals regarding sustainable agriculture. For example, whether altering rumen function to lower methane production can impact an animal’s health, eating patterns and other welfare indicators.

Recommendations on breeding programmes and selection

243. Phenotypic assessment must remain the cornerstone of modern breeding strategies since animal welfare cannot be adequately protected through genomic assessment alone. Industry and academic research should strive to continue to develop and improve quantitative phenotypic and behavioural assessments that inform breeding strategies aimed at optimising welfare. These metrics need to be cost effective, easy-to-use, reliable, reproducible and standardised for each species.

244. Government should support academic research that develops practical and feasible methods of assessing the affective state of animals on farm.

245. To mitigate the risk that the rapid changes in the genetic make-up of livestock leads to unintended adverse welfare consequences at the population level, industry and government should collaborate to establish a national gene bank of germinal products or appropriate tissues taken from healthy animals, free of known hereditary diseases and who have been screened for known infectious diseases. Enough unrelated stock need to be represented to provide sufficient genetic diversity.

Recommendations on data collection and analysis

246. Whilst the AWC acknowledges that some of the data will be commercially sensitive, where possible, stakeholders should collect data in a uniform fashion and make it transparent and freely available as part of sharing responsibility for animal welfare.

247. Industry should develop and implement robust systems that enable commercial farmers to report welfare issues back to breeding companies in a timely and effective manner.

248. Training should be provided to farmers and stockpersons to ensure that they understand the welfare metrics associated with their animals so that they can make breeding decisions that are appropriate for their own context.

249. Whenever animals are kept in harsher environments, to determine their robustness and resilience to different conditions (for example on monitor farms), standards must comply with relevant national animal welfare legislation. In addition, a ‘3Rs’ (replacement, reduction, refinement) approach should be adopted to minimise any possible welfare harms.

250. Government and industry should collaborate to fund further research into how the outputs from Artificial Intelligence and machine learning are verified in the commercial environment.

Recommendations on breeding technologies

251. All stakeholders, including veterinary surgeons, should explicitly consider the welfare impacts of all breeding technologies before using them and take appropriate steps to minimise harms. This includes a) choice of an appropriate animal b) the need to provide appropriate analgesia c) the ethical requirement to use the least invasive technique possible d) use of management practices that will minimise welfare harms including stress and pain.

252. The AWC encourages all stakeholders across all sectors and species to make use of verified new technologies that assess individual animal welfare better, particularly in large group settings.

253. Government and industry should collaborate to fund research on the welfare impacts of new breeding technologies which have been developed since the time of the FAWC 2012 report.

254. Animal welfare assessments of precision-bred animals must be holistic rather than purely trait-based and applied uniformly across research and commercial settings. These should extend across the full extent of a PB animal’s lifetime and across multiple subsequent generations.

255. There is a role for the research community, supported by industry, to ensure and demonstrate that precision livestock technologies are fit for purpose, validated and have a demonstrable benefit to animal welfare.

256. Defra and the Devolved Administrations should coordinate data gathering about the welfare of precision-bred animals.

257. Government should support basic research to determine the complete function of gene products in different environments in order to ensure that precision breeding and editing specific genes does not have any negative welfare consequences.

Recommendations on the welfare impacts of stockpersonship

258. The key role that stockpersons play in the daily care of livestock needs to be recognised. Appropriate and sufficient training, encouragement and monitoring needs to be undertaken especially as new technologies are introduced.

259. Precision livestock technologies should be viewed as an adjunct to good stockpersonship, rather than a replacement.

Appendix 1: AWC membership

Prof Madeleine Campbell*—Chair

Prof Amaya Albalat 

Prof Gareth Arnott*

Miss Emily Craven*

Dr Julian Kupfer*

Mr Stephen Lister*

Dr Jessica Martin 

Mr Charlie Mason 

Dr Romain Pizzi

Dr Pen Rashbass*

Prof Sarah Wolfensohn

Dr Julia Wrathall

Dr James Yeates

[*] = member of the Working Group for this Opinion

AWC is grateful to the AWC Secretariat and APHA and Defra staff who gave assistance.

Appendix 2: Those who gave evidence and assistance

• AB Europe
• Agri Food and Biosciences Institute
• Agriculture and Horticulture Development Board
• All-Party Parliamentary Group on Science and Technology in Agriculture
• Animal Aid
• Animal Equality UK
• Animals in Science Committee
• AquaGen
• ASDA
• Aviagen
• Aviagen Turkeys
• Bakkafrost Scotland
• Benchmark Genetics
• Biotechnology and Biological Sciences Research Council
• British Egg Industry Council
• British Friesian Breeders Club
• British Poultry Council
• British Society of Animal Science
• British Veterinary Association
• Centre for Environment, Fisheries and Aquaculture Science
• Cobb Vantress
• Compassion in World Farming
• Conservative Animal Welfare Foundation
• Ethical Seafood Research
• European Forum of Farm Animal Breeders
• Genus ABS
• Grosvenor Dairy Farm
• Hendrix Genetics
• Holstein UK
• Hubbard
• Hy-Line
• Innovis
• Irish Moiled Cattle Society
• Lakes Free Range
• Landcatch
• Morrisons
• Mowi Scotland
• National Beef Association
• National Pig Association
• National Sheep Association
• Norsk-Kylling
• Nuffield Council on Bioethics
• Old Hall Dairy
• Paragon Veterinary Group
• PD Hook
• Pig Improvement Company
• Queen’s University Belfast
• Rare Breeds Survival Trust
• Royal Society of Biology
• Royal Veterinary College
• RSPCA
• Sainsbury’s
• Salmon Scotland
• Science for Sustainable Agriculture
• Scotland’s Rural College
• Sheep Veterinary Society
• Sustainable Aquaculture Innovation Centre
• Swannington Pig Farm
• The Rare Breed Survival Trust
• The Roslin Institute
• UK Genetics for Livestock and Equines Committee
• Universities Federation for Animal Welfare
• World Animal Protection
• Yeo Valley

Appendix 3: Breeding cycles and breeding systems

Poultry

Poultry breeding

The poultry meat and egg production sectors in UK are serviced by primary breeders supplying the industry with day old breeding stock. These primary breeders are predominantly based in UK and indeed these companies service a global market. For example, it is estimated that over 70% of poultry meat (chicken, turkey and duck) consumed globally derives from UK breeding stock.

The day-old breeding stock they produce supply an assortment of integrated companies rearing broiler, turkey, duck and layer breeders producing day olds for meat production and future table egg laying flocks. The performance of the production flocks in the commercial environment is fed back to the primary breeders in terms of productivity, welfare and economic success (or otherwise). This feedback helps to ensure that the breeding goals set by the primary breeders are fulfilling market and welfare expectations. There is little current interest in genetic modification, instead using a traditional selection process concentrating on seeking useful traits from a broad portfolio of crossbreeds to select the parents of the next generation.

Brief overview of poultry industry

UK annual meat production is estimated as 1.1 billion broilers, 15 million turkeys and 9 million ducks. Broiler meat production has a short supply chain and is predominantly structured around large integrated companies operating a farm to fork strategy with broiler breeders supplying fertile eggs to hatcheries. These are predominantly fast growing strains with some slower growing options to serve smaller markets. Day-old chicks are placed on an assortment of company owned, contract or independent growing farms. Processed birds are marketed as whole birds, portions or further processed products. Most are intensive indoor production with some free range and organic options. Over 90% of production is reared to Red Tractor assurance standards.

Meat turkeys follow a similar structure of production, predominantly double breasted strains for all year production, most for further processing, with a mix of fast and slower growing heritage strains for whole bird seasonal production.

The UK laying hen flock currently comprises some 43 million birds. Laying egg production follows a similar structure of primary breeders supplying day olds for layer rearing and breeder farms to generate day old potential layers, but with a larger number of strains available in the selection portfolio. The UK has the largest percentage of free-range table egg production in Europe, with diminishing colony cage accommodation replaced by a combination of indoor barn and free-range production in line with stated retailer “cage free” commitments.

Breeding selection

Meat birds

Breeding techniques have developed significantly over the last 50 years, starting as phenotypic selection on growth potential. Sibling and progeny testing was then used under challenging conditions to express genetic potential (GxE) and establish breeding value estimations for a broader number of desirable traits. Breeding companies have a broad genotype portfolio of cross-breeds to offer variation in establishing multiple genetic options to satisfy requirements in different markets and countries. Balanced breeding goals are a mix of industry requirements and those of societal stakeholders, seeking sustainable production, economic efficiency and higher welfare to define a set of traits aimed at improvements in production efficiency, welfare, liveability and sustainability. This is achieved by pedigree selection, with core breeding to generate commercial hybrids with stakeholder feedback.

Genomic selection using SNPs and whole genome sequencing is now being used widely to improve the accuracy of the prediction of breeding goals, then multiplying generations for producers. Balanced breeding is also being used to overcome trait antagonism where one gene can control two traits (for example health and bodyweight), selecting birds that score well in both traits through the estimated breeding values which depend on the degree of genetic correlation and heritability. Large amounts of data are generated by producers growing these genotypes to feed back progress on fulfilling genetic potential into the primary breeding programme. The approach remains efficient genetic selection rather than genetic manipulation.

Similar techniques are used in meat turkeys and ducks.

Layers

Genetic selection focuses on over 60 individual traits covering egg production, egg quality, longer laying cycles, improved feather cover, liveability, and behavioural and welfare stability.

Techniques now use genomic information (for example from SNPs) to make more rapid genetic progress and increase the accuracy of traditional selection, leading to targeted step by step improvements. As with meat production, the aim is a balanced programme of selected traits.

Examples of animal welfare benefits and risks from selection breeding strategies

Potential benefits

Improved efficiency of production, reducing costs and meeting sustainability goals assessing GxE effects to maintain bird health and welfare in a variety of production systems.

Potential risks

Selection of production efficiency traits having a negative impact on poultry health and welfare.

Future genetic selection and reproductive strategies

Potential use of AI and other methods of data analysis to assess the outcomes of genetic selection to improve feedback to primary breeders and avoid adverse trait antagonism.

Genome editing is showing some potential in specific areas in layer breeding for example in ovo egg sexing to avoid the killing of male layer chicks by inserting a genetic marker only in the male chicks detected before hatching. The hatched female commercial layer chicks and any eggs produced by them contain no genetically modified material.

Beef and Dairy Cattle

The cattle breeding cycle

• Puberty: Heifers (young females) reach sexual maturity between 9-12 months. However, they are not usually mated at this age.

• Oestrus Cycle: A non-pregnant cow has a 21-day oestrus cycle, coming into “heat” (the period of sexual receptivity) for about 12-18 hours.

• Breeding season: Cattle are able to breed throughout the year. All-year-round calving allows for a steady milk supply, more flexible workload, and easier management of housing and labour demands. Block calving (spring or autumn) simplifies herd management, produces more uniform calf groups and aligns production with seasonal feed availability to lower costs.

• Mating and or Insemination: The cow is mated by a bull or artificially inseminated during heat. In dairy cattle, sexed semen is increasingly used on those cows and heifers with higher genetic merit to increase the likelihood that they produce daughters who can enter the milking herd.

• Gestation: Pregnancy lasts ~283 days (just over nine months).

• Calving: The cow gives birth. Age at first calving is typically 2 years (for dairy and some beef), but 3 or older for some traditional breeds.

• Intercalf interval. In beef cattle, animals are bred about 80 days post calving to maintain a 365-day cycle. However, fertility within the national dairy cattle herd has been an issue. In mid 2000s the average intercalf interval reached almost 425 days. This average across the UK has now reduced to just over 390 days after increased efforts by vets and farmers and breeding strategies such as incorporating AHDB’s female fertility index into breeding strategies.

• Reproduction rate: Most cows give birth to single calves. Twin births occur in roughly 3–5% of dairy cattle and about 1–2% of beef cattle. Holstein-Friesians have a higher twinning rate due to genetic and nutritional factors, while beef breeds tend to have lower rates, partly because of selective breeding for single, healthy calves. Free-martins are infertile female calves whose co-twin is a male calf. It occurs because male hormones from the male fetus masculinise the female’s reproductive tract through shared placental blood vessels. Free-martins occur in over 90% of opposite-sex twins.

Brief overview of the cattle industry in the UK

Both the beef and dairy cattle industries are undergoing rapid change. This is partly driven by fewer, but larger, dairy farms, greater utilisation of sexed-semen and by the increasing use of beef sires on dairy cows. According to Defra statistics, there were just under 9.2 million cattle in the UK in 2024. The female breeding herd accounts ~ one-third of this total. Since 2020, the national beef breeding herd has decreased by almost 12% to just below 1.3 million, while the size of the national dairy breeding herd has remained almost unchanged at just under 1.9 million. Registrations of dairy-breed (for example Holstein Friesian) male calves have also decreased significantly by ~13% since 2023.

A total ~2.85 million cattle were processed at UK abattoirs in 2024. Notably, 45% of UK beef originates from the dairy herd through dairy-beef crosses and cull cows, while the proportion of beef from suckler-bred cattle has steadily declined over the last ten years. Within the national dairy herd, the average milk yield is ~8400litres/cow/year, although the highest-yielding Holstein-Friesians have been reported to produce up to 12000litres/cow/year. In addition to total yields, alteration in selection criteria have resulted in an increase in average milk solids produced per cow (up ~11%) over the past decade.

In the last two decades,  here has been a marked consolidation of dairy herds such that there are now fewer, larger, technologically advanced, and more intensively managed herds: Defra statistics indicate that the number of farms holding 150 breeding cows or more increased from 3415 in 2005 (holding 37% of dairy cattle) to 4232 in 2024 (holding ~71% (1.27 million) of dairy cattle) while over the same period the total number of dairy farms has decreased from ~29,300 to ~15,500. Defra statistics also indicate that a higher percentage of these large dairy farms continually house their herds. Despite this trend, most UK cattle farms (over 70%) for both beef and dairy, still practice seasonal housing, with cattle kept outdoors from Spring to Autumn and then housed during winter months.

Animals intended for the beef market are managed in different ways depending on factors including cattle type, microclimate, soil type, grass growth and market forces. They may broadly be classified into three categories: intensive (12–15 months finishing time), semi-intensive (15–20 months) and extensive (over 20 months). In general, entire bulls from continental breeds are most suited to intensive systems (so-called ‘barley beef’ or ‘barley bulls’) and may also be housed all their life. In contrast, British traditional native breeds have been selected to thrive in outdoor systems, even if they are intensively finished. Some supermarkets are now offering sustainable farming initiatives that link premiums to genetic merit for efficiency traits alongside other welfare and productivity characteristics.

Cattle Types include

• Dairy breeds: Holstein-Friesian dominates (90% of dairy herd). Other breeds include Jersey, Guernsey, Ayrshire, Montbéliarde and crosses including with Holsteins to improve hybrid vigour.
• Beef breeds: Native breeds include Aberdeen Angus, Beef Shorthorn and Hereford. These are hardy animals that, depending on breeding and management, can finish well on grass. Continental breeds including Belgium Blue, Limousin Charolais and Simmental are larger, leaner animals with higher muscle yield. The double-muscle phenotype in Limousins and Belgian Blues results from myostatin gene mutations. Different variants (E226X in Blues, F94L in Limousins) cause varying dystocia levels –– Belgian Blues more often experience severe calving difficulties requiring caesareans, while Limousins show milder effects. Composite breeds such as Stabiliser are also increasingly popular, as are cross breeds.

Bull management

Breeding bulls, when not being run with cows, are often housed individually for their own and their handler’s safety. The Health and Safety Executive ban bulls of recognised dairy breeds (for example Ayrshire, Friesian, Holstein, Dairy Shorthorn, Guernsey, Jersey and Kerry) in all circumstances from being at large in fields crossed by public rights of way or other types of permitted access. They also ban beef bulls from fields or enclosures with footpaths unless accompanied by cows or heifers. When not running with cows, beef stock bulls may be kept outdoors with a small group of other bulls or steers (castrated males) provided they are not kept in fields with footpaths. Bulls from dairy breeds are often not kept on individual dairy farms because of safety and cost.

Breeding Strategies and Technology Adoption

AHDB and Egenes provide national genetic evaluations and their role in performance recording and genetic improvement schemes remain crucial for identifying elite genetics and improving the national herd’s health and productivity. Performance monitoring has been adopted by ~85% of dairy farms (activity meters, yield recording) versus ~40% in beef enterprises. Genomic testing and genetic profit are currently practised on 70% dairy and 25% beef suckler herds. In dairy, the PLI (Profitable Lifetime Index) balances production, fertility, lifespan, and health traits. In beef, the SBI (Suckler Beef Index) and DBI (Dairy-Beef Index) predict profitability from growth rate, feed efficiency, carcass traits, and calving ease. Use of these indices to identify suitable breeding stock is also reducing the number of animals that are culled involuntarily for infertility, lameness or poor udder health.

Reproductive technologies (for example artificial insemination, sexed semen and embryo transfer) are used by 95% of dairy farms but only 30% of beef farms. Increased use of technology such as mid-infrared (MIR) spectroscopy of routine milk recording samples can help assess traits such fat and or protein yield, fertility, methane output, and energy balance in dairy cattle.

Image analysis combined with artificial intelligence can assess gait patterns, posture and weight distribution to detect subtle changes prior to clinical lameness. Similarly, image analysis and or robotic milkers with conductivity sensors can predict mastitis 24-48 hours prior to visual and or clinical detection. Cattle feed conversion efficiency (FCE) calculations used data obtained from automated feeders and sensor systems in research and breeding herds. Methane emissions are evaluated using respiration chambers, laser and sniffer technologies, or genetic proxies linked to feed efficiency and rumen traits.

Over the next five years, assays targeting milk biomarkers for disease resistance, immune competence, heat stress tolerance, and detailed fatty acid or metabolomic profiling may become commercially viable.

Examples of animal welfare benefits and risks from selection breeding strategies

The key challenge is to balance productivity with robust, healthy, adaptable animals suited to their environment.

 Welfare benefits:

• Improved disease resistance (for example, lower mastitis, lameness, metabolic disorders, bovine tuberculosis and Johne’s disease).
• Enhanced fertility and calving ease reducing dystocia.
• Greater heat tolerance and adaptability to management systems.
• Selection for docility and temperament, improving handling safety and reducing stress.
• Polled genetics eliminating painful dehorning.
• Longer productive lifespan and reduced involuntary culling by selection for robustness and resilience traits.

Welfare risks

• Potential for calving difficulty from use of double-muscled sires
• Metabolic stress and lameness from breeding for extreme milk yield
• Trade-offs between yield and immunity
• Reduced genetic diversity, increasing vulnerability to disease
• Overemphasis on production traits leading to compromised reproductive performance or longevity
• Social behaviour changes affecting herd dynamics
• Unintended side effects from genomic selection if welfare traits are not included in breeding goals
• Early sexual maturity with immature body size
• Compromised thermoregulation in lean animals

Sheep

The sheep breeding cycle

• Most sheep are seasonal, short‑day breeders. Most ewes cycle naturally as daylight hours shorten. As well as depending on the daylength in the region where they are kept, the start date and duration of the natural mating season also vary between the different breeds.

• Gestation: ~147 days

• Lambing: Typically January–April in lowlands; April–June in uplands.

• Oestrus interval: 17 days (range from 14-19 days) with the duration of oestrus (ewe receptive to the ram) for approximately 30 hours (range 24-36 hours) depending on breed.

• Out-of-season breeding is possible using artificial lighting, hormones, and certain breeds (for example, Dorset Horn). Onset of the breeding season can also be brought forward using the “ram effect”. This is when non-cycling ewes are stimulated to ovulate by pheromones produced by male sheep (either entire or vasectomised (teasers)). The ram effect relies on ewes and rams being totally isolated from each other for at least six weeks prior to the planned mating season.

• Reproductive rate: 1.3-2.0 lambs per ewe. The preferred average number of lambs per ewe varies depends on the individual farm system but it is a key determinant for farm profitability. As an ewe has 2 teats, twin lambs are often considered the optimum number. However, first time lambers, ewe lambs and those kept on poorer quality grazing will often have single lambs. Larger litter sizes (3 or more) can lead to high rates of stillbirths, weak lambs, and decreased individual lamb survival due to competition for milk and maternal attention. Excess lambs may be fostered onto other ewes or else hand-reared.

Brief overview of sheep industry in UK

The sheep industry is diverse in relation to the farm type, management system, lambing season and the age that animals are ready for slaughter. The type of sheep kept on any particular farm is usually based on a variety of factors that includes geographic location, land quality, local climatic conditions, market price and demand, governmental policy including environmental schemes and sustainable farming incentives, personal preference, labour availability and cultural values.

Defra statistics indicate there were ~31 million sheep in the UK in 2024. This is a decrease of 5.1% since 2020. The majority of sheep in the UK are bred for meat. In 2024, UK abattoirs processed 12.85 million sheep and lambs. This is 9% lower than the 2019–2023 average of 14.1 million head. A tiny minority of sheep are also bred for dairy, wool and environmental services (conservation grazing or as part of an arable rotation) or are kept as pets.

There is a gradual uptake by farmers for individual animal performance monitoring using electronic identification (EID) for traits such as body condition scores and growth rates. However, more advanced technologies tend to only be used on relatively few animals with high value genetics and or for research purposes. Furthermore, the fragmented nature of the UK sheep industry—many small, geographically dispersed flocks using different breeds and limited data-sharing—has slowed national genetic gain compared with other countries that have more integrated systems (for example, New Zealand).

Ram management

Outside the breeding season, rams are typically maintained in bachelor groups or with wethers (castrated males) for company. Sturdy fencing and strategic placement minimise unplanned pregnancies.

Types of sheep

There are over 60 native sheep breeds in the UK. This increases to well over 100 when non-native breeds, crossbreeds and composite types are included. Some traditional flocks are also being replaced with imported breeds that may be hardier, have fewer input costs and lower labour care requirements. Each breed has its own characteristics and suitability for the diverse habitats and farming systems across the UK, but they can be broadly divided into four groups: hill, upland, lowland and primitive.

• Purebred breeding: Maintains breed identity and characteristics that are regulated by breed societies.

• Crossbreeding: F1or F2 cross for hybrid vigour

• Composite breeds: Stable populations produced by crossing different breeds over multiple generations and selected for multiple favourable characteristics (for example, improved parasite resistance or wool shedding)

The Stratified sheep system: This is unique to the UK. Historically, each tier has been very dependent on the other two. It maximises the use of regional environments, but contributes to the fragmentation of the sheep sector, with many small, independent breeders. This has made genetic progress more difficult and inconsistent across the national flock.

• Tier 1: hardy hill breeds are kept in relatively harsh habitats

• Tier 2: upland flocks, where they may be put to rams of specialised long-wool breeds to produce cross-bred breeding ewes such as mules or Welsh Halfbreds, depending on the ram breed used

• Tier 3: Tier 2 offspring crossed with terminal sire rams to produce slaughter lambs.

Breeding Selection strategies include

• Maternal traits: Important traits for ewes within the breeding flock. These include fertility, milk production, mothering ability.

• Terminal traits: Growth rate, carcass conformation. RamCompare is the UK’s national terminal sire progeny test. It uses a large dataset of abattoir data to identify sires whose genetics improve lamb carcass traits including Days to Slaughter, Carcass Weight, Conformation, Fat Class, Primal Yield, and Meat Tenderness. RamCompare generates estimated breeding values (EBVS) and an overall carcase merit index for rams. However, using terminal-type breeds to generate replacements for the ewe breeding flock can have detrimental consequences on the performance of the maternal flock.

• Wool traits: selection for finer wool OR self-shedding breeds

• Emerging selection parameters: reduced methane emissions, improved disease resistance (for example internal parasites, footrot), feed efficiency.

Examples of animal welfare benefits and risks from selection breeding strategies

Potential benefits:

• Faster growth enables lambs to be finished pre‑puberty. This reduces need for castration in many flocks.
• Breeding short‑tailed types reduces reliance on tail docking to reduce risk of flystrike.
• Self-shedding wool reduces the risk of flystrike and removes the need for shearing.
• Genetic resistance to disease lowers use of antibiotic and anthelmintics.

Potential Risks:

• Selecting strongly for growth or muscling can increase dystocia (lambing difficulty).
• Narrow gene pools can reduce resilience to future disease or climate stresses.
• Intensive selection may affect maternal instincts or adaptation to hill environments.

Advanced genetic selection and reproductive technologies used by UK sheep farmers has very limited uptake compared to some other countries (for example New Zealand, Australia). Advanced Technologies include

• Genomic selection: DNA testing for breeding values

• CT scanning: Carcass trait evaluation of live rams. Rams need to be sedated and placed on back while scanning takes place

• Methane emission assessment: Direct measurement of individual animals using mobile portable accumulation chambers (PACs)

• Artificial insemination: Limited uptake and use (1-2% of flocks, 0.3-05% of breeding ewes). It is labour intensive and results in lower conception rates than natural service.

• Embryo transfer: Rare in UK: used for high-value genetics, genetic imports, research programmes and rare breed conservation. It has variable success rate in sheep and has a high cost per pregnancy achieved.

Pigs

The pig breeding cycle

• Sows and gilts are non-seasonal and polyoestrous (some pigs do show some seasonal declines in fertility, perhaps reflecting ancestral traits as wild boar are seasonal breeders with a tendency to farrow in spring).

• Gestation: 115 days (3 months, 3 weeks, 3 days). Range 111-120 days.

• Parturition: all year round

• Oestrus interval: 21 days (18-24). Oestrus lasts 36-48hours in gilts and 48-72 hours in sows

• Normal uterine physiology reestablished 20-25 days post-partum and most sows exhibit oestrus 3-7 days after weaning

• Reproductive rate: differs between indoor and outdoor herd. Gilts often have smaller litters with parity size peaking around 4th – 7th farrowing. Given large litter sizes, a degree of preweaning mortality is expected (for indoor herds, pre-weaning mortality is 12.5% on average, and 9.8% in the best-performing 10% of herds. For outdoor herds, the average is 12.4%, with the top 10% of herds having pre-weaning mortality rates of 10.3%)

	Indoor	Indoor	Outdoor	Outdoor
Key Performance Indicator (KPI))	Top 10%	Average	Top 10%	Average
Average weaning age (days)	25.9	26.6	26.4	26.5
Total pigs born per litter	17.9	16.1	14.9	13.5
Litters per sow per year	2.3	2.2	2.3	2.2
Non-productive days	16.6	26.2	13.4	28.7
Pigs weaned per sow per year	34.2	28.3	29.9	24.7

Brief overview of the pig industry in UK

The pig sector is mostly considered to be intensive production, although there is plenty of scope for non-intensive production, often in the form of small holders and those farming rare breeds. Intensive production is usually divided into indoor and outdoor herds, where indoor animals usually remain indoors for their whole life, and outdoor herds may be outdoor bred and then move indoors for finishing. Type of pig and farm management on individual farms are usually based on a variety of factors that includes geographic location, land quality, local climatic conditions, market price and demand, governmental policy including environmental schemes and sustainable farming incentives, personal preference, labour availability and cultural values.

Defra statistics indicate that the number of pigs in the UK has remained relatively stable at 4.7 million in 2024, helped by a 0.9% rise in the number of fattening pigs. The number of breeding pigs has decreased by 1.7% to 421,000. The female breeding herd which accounts for 78% of breeding pigs fell by 3.1% to 327,000. Within this, gilts saw the largest decrease, down 11% but decreases were seen across each category. Other breeding pigs saw an increase in 2024, rising by 3.7% from 90,000 t to 93,000.

Nearly 50% of the UK breeding herd is owned by the large integrated companies such as Cranswick and Pilgrim’s which has a large impact on genetic gain. The pig sector is quite volatile and hugely affected by disease, grain prices and other factors, In addition, there may be a significant period of change if  farrowing crates are banned (however, it should be noted that no decision on banning farrowing crates has been made either by the UK government or by the Devolved Administrations).

Boar management

Boars can either live with the group, be introduced for mating, kept as teasers or just for their presence to stimulate oestrus and then AI is used. There are several boar studs in the UK for collecting semen for AI. Many mature boars are individually housed.

Types of pig

There are many different types of pig in the UK. Traditionally commercial sows were Large White Landrace cross mated with a terminal sire such as a Hampshire for fat pigs, but increasingly genetics have changed for productivity purposes, with the large integrated companies producing their own hybrid breeds to suit their needs and requirements. For example, Rattlerow has the WhiteRoc, a female line created from Large White, Landrace, and Duroc crosses, and terminal sires like the MaxiMus, which are derived from Piétrain and other breeds.

• Purebred breeding: Maintains breed identity and characteristics that are regulated by breed societies

• Crossbreeding: F1 or F2 cross for hybrid vigour

• Composite and or hybrid breeds: Stable populations produced by crossing different breeds over multiple generations and selected for multiple favourable characteristics (for example mothering ability, litter size, carcase shape)

Breeding Selection strategies include

• Maternal traits: Important traits for sows within the breeding herd. These include fertility, milk production, mothering ability.
• Terminal traits: Growth rate (focus on growth and leanness), carcass conformation.
• Emerging selection parameters: improved disease resistance (for example PRRS), feed efficiency.

Examples of animal welfare benefits and risks from selection breeding strategies

Potential benefits:

• Faster growth enables pigs to be finished prepuberty. This reduces need for castration (as ‘boar taint’ of meat occurs only after puberty).
• Genetic resistance to disease lowers use of antibiotic and anthelmintics.

Potential Risks:

• Selecting strongly for growth or muscling can increase lameness.
• Narrow gene pools can reduce resilience to future disease or climate stresses.
• Larger litter sizes may increase pre weaning mortality.
• Intensive selection for carcass traits may affect maternal instincts.

Advanced genetic selection and reproductive technologies are currently used in the UK and the sector appeared keen to embrace future technologies such as genomic editing. Advanced Technologies include

• Genomic selection: DNA testing for breeding values
• Artificial insemination: mostly using chilled semen
• Improved phenotypic assessment monitoring individuals (both of live animals and carcasses), image processing and artificial intelligence.

Atlantic Salmon

The salmon production cycle

Atlantic salmon are anadromous. This means that in the early stages of life they live in freshwater while their main growth phase occurs in seawater. In the wild, adults return to freshwater to reproduce. The timing of these different stages can be quite variable with wild fish spending between one and four years in freshwater, and between one and three years in the ocean. Although this variation in maturation is beneficial to wild population survival, it is undesirable in farmed populations. Maturation rate is controlled by several factors including genetics, body composition, metabolic status, photoperiod (light-dark cycle) and temperature.

Salmon farming occurs in both freshwater (hatchery and nursery) and seawater (on-growing to slaughter age (often called “harvesting”)).

The production cycle:

• Broodstock age. 3-5 years. Potential broodstock are selected in spring–summer and held until autumn–winter for stripping. Broodstock are usually transported to freshwater sites for acclimation prior to “stripping” (gamete collection).

• Gamete collection and IVF. Anaesthetised or freshly culled adult females and males are manually stripped of eggs and milt (sperm) – either by gentle abdominal pressure or (if culled) by slicing open the abdomen. There are several thousand eggs per fish (number varies with maternal body size). Collected ova are fertilised with milt under controlled IVF conditions.

• Freshwater hatchery stage - 1. Fertilised ova are incubated in cold, clean oxygenated water. 2. Alevin stage: Hatched larval stage with a large yolk sac that provides all their necessary nutrients. 3. Fry stage: Free swimming stage with yolk sac completely absorbed. 4. Parr stage: Juvenile salmon develop characteristic vertical bars (parr marks on their sides).

• Smoltification: The physiological transformation of parr into smolts (fish able to survive in seawater). These adaptations include hormonal changes, silvering of skin, altered body shape, and development of seawater tolerance through gill and kidney adaptations. The salmon industry controls the life cycle and the timing of smoltification using a range of methods including genetic selection and adjusting the photoperiod.

• Seawater stage (smolt to slaughter): Smolt are transported to sea pens to continue their growth phase. The normal seawater production period has been rapidly reducing and is now between 10  – 22 months. Fish are slaughtered at various ages and times of year, depending upon growth

Brief overview of the UK Atlantic Salmon industry (impact of farming on the wider environment and wild stocks are not included in this section)

Salmon Farming is an international business and several of the 14 companies that run farms in Scotland also have facilities in other countries. Over the past few years, salmon farmers have experienced increasingly challenging environmental conditions in the waters around Scotland driven, in part, by rising seawater temperatures. The industry is therefore selecting and breeding more robust salmon that are faster growing so that they can avoid a second summer and autumn at sea. In addition to this genetic selection, closed containment systems in sea, vaccinations, “lice lasers” and submerged pens are also being developed. Land based (full-cycle) salmon farming has also attracted increasing interest within the industry. Currently, only few land-based facilities exist world-wide and there are none in the UK, although at least one has been planned.

According to Scottish Government statistics, in 2024, 55.7 million ova were stripped from broodstock in GB, compared to 11.6 million ova in 2015 (there was a dramatic increase in number of ova stripped between 2019 and 2021). in 2024, 89.5 million ova were laid down to hatch (36.88 million derived from GB stock; 52.6 million (59%) imported and 17,000 from GB wild broodstock). This compares to 2015 when 68.2 million ova were laid down to hatch, but over 90% of these were imported. It is expected that over the next few years, more companies will become self-sufficient in egg production as more broodstock facilities are completed within Scotland.

In 2024, ~35 million salmon were slaughtered to enter the human food chain. This consisted of 52,000 fish (174 tonnes) of year 0 (2024 input fish), 21.5 million fish (~113,000 tonnes) of year 1 (2023 input fish) and 13.4 million fish (~79,000 tonnes) of year 2 (2022 input fish).

In 2022, the last year for which survival can be calculated, the survival rate from smolt input to slaughter for the food chain was 61.8% of input fish. The statistics relating to this high mortality figure include all fish not slaughtered for human consumption. This includes fish which had escaped, been culled for production reasons, removed for sampling purposes, statutory culls or selected for broodstock production.

Cleaner Fish

A major industry change over the last 12 years is the use of “cleaner” fish as a biological control for parasitic sea-lice. These cleaner fish are farmed (and wild-caught) lumpfish and wrasse.

Breeding Strategies and Technology Adoption

Atlantic salmon domestication is relatively recent. This has enabled the industry to learn from the technologies and principles developed in the terrestrial livestock industry. Hopefully they can build on this and avoid many of the historic mistakes that have previously occurred in livestock breeding. Balanced breeding is important. Current selection traits include those that select salmon with

• faster growth rates and improved feed conversion efficiency which can lead to increased production efficiency (by reducing the time it takes for salmon to reach market size). These combined with ensuring smolt are larger when they are moved to the seawater significantly reduce the time that salmon need to be at sea where they are at risk from parasites and infections.

• greater natural resistance to common diseases and parasites. These include Infectious Pancreatic Necrosis, Cardiomyopathy Syndrome and sea lice. In addition to improving welfare, this should also reduce the need for antimicrobials or other medical interventions.

• improved tolerance for stress. that is select fish that exhibit lower stress responses to handling, transportation, and environmental changes.

• are better adapted to warmer water temperatures or altered nutrient availability (due to climate change).

• optimal physical conformation. These include selection for strong bones, well-developed muscles, and proper body proportions as this reduces the likelihood of structural defects, injuries, and health problems.

• desirable behavioural traits such as calm temperament, social compatibility, and adaptability to various husbandry conditions. Such animals are better equipped to cope with stressors and interact positively with their environment and conspecifics.

• optimal reproductive fitness which can ensure successful reproduction and genetic diversity within populations (breeding individuals with traits such as high fertility, maternal instinct, and offspring viability can contribute to the long-term welfare of future generations).

• impact body shape and muscle composition leading to greater fillet yield, thus increasing overall value of fish and reduce waste.

• favour the production of salmon with characteristics that are in line with consumer preferences (for example, taste, texture, and appearance), thereby enhancing marketability.

• External fertilization enables aquaculture to employ specialized breeding techniques including single-sex production and triploid creation. These methods prevent sexual maturation and reduce aggression. The industry claim this may reduce mortality, enhance welfare and prevent wild breeding. Currently utilised in trout farming, these techniques may increasingly be adopted in salmon aquaculture.

• Artificial Intelligence and data capture and or management systems have become increasingly relevant in aquaculture research and production. Examples include:
  • Vision systems to monitor the growth conditions and behaviour of the livestock.
  • Data extraction and integration to provide more comprehensive and real-time information about the farming conditions, enabling better decision-making.

• Fish Tagging. This involves attaching a tag to the fish to monitor individual movement and behaviour.

• Transgenesis, genetic modification and genomic editing are not currently permitted in the UK.

Welfare Risks

Despite the increased use of balanced breeding (see section above), historically there have been harmful consequences associated with selective salmon breeding. For example, selective breeding for faster growth has been reported to lead to - an increased occurrence of lens cataracts, skeletal defects, deafness, reduced immune function, a higher risk of metabolic disorders and increased susceptibility to diseases. - abnormal heart development and function, making salmon more susceptible to cardiac failure during stressful procedures such as crowding, grading, lice treatments, and transportation. - early sexual maturation, causing stressful behavioural disturbances and earlier male-to-male fighting.

In addition, loss of genetic diversity by using only limited number of broodfish could have long-term consequences for health and welfare of the farmed salmon population

Some procedures for example producing triploid salmon may reduce their physiological robustness and resistance to disease.

To date, comparatively little research has been undertaken that assesses fish behaviour and pain perception. These fundamental welfare concerns cannot be properly assessed without developing robust, reliable, reproducible metrics that can be easily used within a commercial setting.

Appendix 4: Bibliography of peer reviewed and grey literature

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Appendix 5: Meetings and visits with stakeholders

Meetings and Site Visits

• AB Europe
• AquaGen salmon hatchery
• Aviagen
• EGENES
• Grosvenor Dairy Farm
• Hendrix Genetics
• Hubbard
• Hy-Line hatchery
• Innovis
• Landcatch
• Old Hall Farm
• Pig Improvement Company
• Swannington Pig Farm
• The Roslin Institute

Roundtables

• Academics and Veterinarians
• Animal Welfare NGOs
• Aquaculture
• Breeding and Genetics Industry Representatives
• Cattle, Dairy and Sheep
• Pigs and Poultry
• Supermarkets

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