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Medical Index
First Posted June 29, 2010
Jul 30, 2010

Contagious Equine Metritis (CEM)

Contagious Equine Metritis (CEM) is a venereal infection of the genital tract of horses brought on by the Taylorella equigenitalis bacteria. Passed on through sexual contact, according to Robert N. Oglesby DVM, the disease was first reported in 1977 on horse breeding farms in England and was found in 1978 by Dr. C.E.D. Taylor in horses imported from Europe into the state of Kentucky in the United States. A second American outbreak occurred a year later in Missouri but in both cases, the diseases were quickly eradicated. The American Association of Equine Practitioners has advised that the disease has also been found in a few but limited cases in California, Virginia and New Jersey. On December 17th 2008 a case was reported by USDA-Aphis to the OIE in a 16 year-old Quarter Horse stallion standing at stud in Kentucky who had previously been located in Texas. Contagious Equine Metritis has also been found in Japan, Germany, France, Netherlands, Scandinavia Bosnia and Morocco.


Signs in mares appear ten to fourteen days after breeding to an infected or carrier stallion. A gray to creamy vulgar discharge mats the hair of the buttocks and tail, although in many cases, the discharge is absent and the infection is not apparent. Most mares recover spontaneously, although many become carriers. Infected mares are usually infertile during the acute illness. However, the infertility only lasts a few weeks, after which pregnancy is possible. Stallions do not show signs of infection. The first indication of the carrier state is the appearance of Contagious Equine Metritis and/or lack of pregnancy in the mares covered by the stallion.


The Diagnosis of Contagious Equine Metritis is made by taking cultures from all accessible sites. In mares, this includes the endometrium, cervix, clitoral fossa and sinuses. In stallions, cultures are taken from the skin folds of the prepuce, urethral fossa, urethra, and the pre-ejaculatory fluid. All samples should be refrigerated and transported to an approved testing laboratory within 48 hours of collection.

Blood tests for mares are available for detecting antibodies to Taylorella equigenitalis. Blood tests are not possible for stallions. These tests become positive 10 or more days after infection. If positive, they only indicate that the mare has had the disease in the past, and do not indicate whether the mare is a carrier now.


Taylorella equigenitalis is susceptible to most antibiotics, although the carrier state in mares is difficult to eliminate. Most mares with acute endometritis recover spontaneously. Recommended therapy is to infuse the uterus with an antibiotic such as penicillin, cleansing the clitoral area with 2% chlorhexidine solution and then applying chlorhexidine or nitrofurazone ointment to the clitoral fossa and sinuses. The entire treatment is repeated daily for five days.

It is relatively easy to eliminate the carrier state in stallions using local disinfectant. With the penis dropped and the glans extended from the foreskin, the shaft of the penis, including the folds of the prepuce and the urethral fossa, should be cleansed daily for five days with a 2% chlorhexidine solution. After drying, nitrofurazone cream is applied to these areas.

For More Information:

Contagious Equine Metritis

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