Wednesday, April 4, 2012 - Mark Humph Mark Humph


Defra have confirmed isolation of Taylorella equigenitalis (the Contagious Equine Metritis organism) by identification of the agent using PCR and culture from clitoral swab samples taken from an asymptomatic 16-year-old Thoroughbred mare in Gloucestershire.  According to the owner, this retired National Hunt race mare has never been covered by a Thoroughbred stallion and has never been pregnant, but was unsuccessfully inseminated with semen from a non-Thoroughbred stallion last season. This non-Thoroughbred stallion has also been confirmed positive using PCR and culture.
The only other mare on the owner's premises is a 9-year-old non-Thoroughbred mare that is reported to have been previously neither covered, nor inseminated.  Clitoral swab samples taken from this mare suggest that she is PCR positive also and the veterinary inquiry suggests that she may have been infected indirectly by shared grooming equipment. All positive horses are under official breeding restrictions, and must be treated and tested according to the HBLB Codes before these restrictions will be lifted.
Veterinary surgeons attending Thoroughbreds and horses of other breeds should continue to recommend that their clients follow the Horserace Betting Levy Board's Codes of Practice (, making sure that all stallions, teasers and mares are specifically tested and cleared negative for CEM before they are used for any breeding purposes.

These Codes of Practice are designed to help maintain freedom from CEM and other important equine infectious diseases, and after over 30 years of consistent use in UK have proved highly successful.  The Codes are a clear example of the effective leadership in disease control shown by the equine industry, with support from Defra.  Also, and particularly following this news, veterinary surgeons should help make sure that their clients clearly understand and apply these well established principles of biosecurity, and more specifically to consider and take steps to minimise the risks of transmission from any sectors of the horse breeding industry that may not fully apply the Codes of Practice.
In view of this recent report, all breeders must remain even more vigilant.  There is no evidence to suggest that this outbreak involves the UK's Thoroughbred breeding industry where the application of the Codes is standard practice.


The International Collating Centre (ICC) understands that a) the Thoroughbred mare identified recently as positive for Taylorella equigenitalis, the cause of CEM, has never been covered by a stallion, but was artificially inseminated (AI) for the first time in 2011 with semen from a non-Thoroughbred stallion and b) the second contact mare has never been bred by either natural covering or AI. Evidence to date, therefore, suggests that there has been no incursion of CEM into the Thoroughbred breeding industry, in which routine pre-breeding screening for venereal pathogens is conducted annually in the breeding population and which continues to confirm the absence of CEM in Thoroughbreds. The epidemiological investigation of the situation is continuing by Animal Health Veterinary Laboratories Agency (AHVLA).


A case of contagious equine metritis was reported in Gloucestershire, UK by DEFRA on 28th March 2012. The affected horse is a 16 year old Thoroughbred mare and a diagnosis was confirmed by PCR and bacteriology on a clitoral swab during routine pre-breeding testing. A second thoroughbred mare, the only other horse on the premises, is currently undergoing testing and neither of the horses have shown clinical signs of disease. Epidemiological investigations are taking place which are focusing on the affected and contact premises. The last case of CEM in the UK was reported in 2010. 

Contagious Equine Metritis

  • CEM is a venereal infection that causes a discharge from the vulva, resulting from inflammation of the uterus. Infected horses can be treated with antibiotics and recover.
  • CEM cannot be transmitted to humans.
  • The infection is easily controlled and movement restrictions on the horse and in-contacts have been put in place.
  • It is a sexually transmitted equine disease. However, indirect transmission can also occur for example through contaminated breeding equipment.
  • The spread of infection is controlled by preventing the mating of infected horses, treating the infection, re-testing several times to check the infection has cleared up before resuming mating, and applying strict hygiene measures when handling the horses involved.
  • Horses are tested before they are exported so there will be limited trade implications.
  • Further details about Contagious Equine Metritis can be found at
  • The Horse Racing Betting Levy Board has also produced a Codes of Practice with Defra on preventing disease

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