Contagious equine metritis: how to spot and report the disease

How to spot contagious equine metritis, what to do if you suspect it and measures to prevent its spread.

Applies to England, Scotland and Wales

Contagious equine metritis (CEM) is a venereal disease that affects horses, donkeys, mules, zebras and other members of the equid family.

It does not affect humans.

Latest situation

A case of CEM was confirmed in a stallion at a premises in Gloucestershire on 3 February 2022.

The stallion is being treated and follow up testing is on-going. No other animals have been identified as being in close contact with the stallion.

The last outbreak of CEM in Great Britain was in June 2021 in Devon.

How to spot CEM

Stallions do not show clinical signs of the disease, but they can carry it.

In mares you should look out for discharge from swollen genitals, especially 1 to 6 days after mating.

Infected mares may also be temporarily infertile, so if your animal is failing to get into foal, get it examined by a vet.

Laboratories and CEM

CEM is a reportable disease for laboratories. If a laboratory suspects the disease is present in a sample from your animal, they must contact their nearest Animal and Plant Health Agency office immediately. Failure to do so is an offence.

How CEM spreads

CEM spreads from horse to horse during mating. It can also spread when horses are artificially inseminated.

Preventing and controlling CEM

Preventing CEM

You can use the Horserace Betting Levy Board contagious equine metritis code of practice to help prevent infection and to stop the disease spreading.

You can also prevent CEM by practising strict biosecurity on your premises.

If you suspect CEM

You should:

  • tell your vet immediately - they may take samples from your horse for lab testing
  • isolate any horses you think are affected
  • stop the suspect horses mating
  • avoid using semen from stallions with suspected or confirmed infection

If CEM is confirmed

CEM can be treated with antibiotics. There are no public health implications.

Where owners of affected horses agree to comply with the HBLB code of practice, the affected animal and all contacts will be tested and treated following advice from industry disease experts and the British Equine Veterinary Association. The premises will be restricted from exporting any horses or equine germinal products until the cases are successfully resolved. These procedures have been in place since April 2020, following an initial pilot.

Where owners choose not to comply with the code of practice, the outbreak will be controlled in line with the contingency plan for exotic notifiable diseases.

Further information on prevention and control

What happens when a notifiable disease is suspected or confirmed.

Legislation relating to CEM

The main domestic legislation on CEM is the Infectious Diseases of Horses Order 1987.

Updates to this page

Published 26 August 2014
Last updated 4 February 2022 + show all updates
  1. Updated to reflect that a case of CEM was confirmed in a stallion at a premises in Gloucestershire on 3 February 2022.

  2. A third case of Contagious Equine Metritis (CEM) confirmed in West Devon.

  3. In the latest situation section changed Devon to West Devon.

  4. Updated to reflect that on 9 June 2021 a stallion at an equine premises in Devon tested positive for Contagious Equine Metritis (CEM).

  5. AHVLA documents have been re-assigned to the new Animal and Plant Health Agency (APHA).

  6. First published.

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