Researchers at the Gluck Equine Research Center will publish a study this fall on contagious equine metritis (CEM), a sexually transmitted disease in horses. Stallions are asymptomatic carriers of Taylorella equigenitalis, the causative agent of CEM, while mares may develop signs of an endometritis/cervicitis/vaginitis following exposure to an infection with this bacterium.

The study set out to investigate if antibiotics in a semen extender, which is used for artificial insemination, inhibit the growth of T. equigenitalis. Preliminary results would indicate that presence of antibiotics in an extender is likely to greatly reduce the risk of spread of CEM from a carrier stallion to a mare bred by artificial insemination with contaminated semen.

The study was undertaken shortly after several Quarter Horse stallions in Kentucky tested positive in December 2008 for T. equigenitalis. All the stallions in question were used solely for breeding via artificial insemination.

To date, 21 stallions have tested positive for T. equigenitalis nationwide and a total of 715 mares were determined to have been exposed to CEM. Of the 715 mares exposed to CEM, five were confirmed carriers, of which several were reported to have developed a vaginal discharge after being bred in 2008.

Signs of CEM can become apparent in a mare about a week after breeding. Affected mares will develop signs of inflammation of the reproductive tract, frequently accompanied by a variable amount of vaginal discharge.

CEM can have a significant economic impact on a horse breeding industry. Mares infected with T. equigenitalis experience short-term infertility with or without clinical signs of the disease. Some mares can become pregnant even though persistently infected with the bacterium. Abortion at about seven months gestation is a very rare sequel to infection in the pregnant mare.

CEM was first recognized in Ireland and England in 1977 as a new disease affecting the Thoroughbred industry. In 1978, the first CEM outbreak occurred in Lexington, Ky., following the importation of two stallions from France the previous fall. This triggered a response from the USDA requiring regulatory control over imported stallions and mares from CEM-affected countries. Today, imported stallions and mares from such countries are routinely tested for CEM. The current procedure is based on bacterial culture of T. equigenitalis and also in the case of stallions, test breeding to two mares. T. equigenitalis can be difficult to isolate in the laboratory, and repeated samples may be required to confirm the negative infectivity status of a stallion or mare. For this reason, part of the research being undertaken at the Gluck Center is focused on developing and validating a PCR test to aid in the diagnosis of CEM; interim findings of the study are promising.

Claudia Klein, DVM, is a staff veterinarian and graduate student in reproduction at the Gluck Equine Research Center. Jenny Blandford is the Gluck Equine Research Foundation Assistant at the Gluck Center.

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