CA21220 - Plant and Machinery Allowances (PMA): meaning of plant and machinery: animals
You should check the other guidance available on GOV.UK from HMRC as Brexit updates to those pages are being prioritised before manuals.
Accept a claim for PMAs on an animal if the animal functions as apparatus with which the trade is carried on and it has an expected life of 2 years or more. For example, it is likely that a horse used in a riding school or show jumping business, a guard dog or a circus animal is plant.
Do not accept a claim that a farm animal such as a horse, cow or sheep is plant, unless it is a working animal such as a sheep dog. Farm animals are normally trading stock and their cost is revenue expenditure that bars a capital allowance claim. Alternatively, the farmer may have made an election for the herd basis under ITTOIA/S111 or CTA09 /S122 (formerly ICTA88/SCH5/PARA2). This also means no capital allowances may be made claimed on these animals.
You should treat a share in an animal in the same way.