Contagious Equine Metritis - Mare

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Also Known As

Venereal disease in mare


Contagious equine metritis in mares is a treatable, highly contagious venereal disease that causes an acute purulent metritis with mucopurulent vaginal discharge ten to fourteen days after the mare has been bred to an infected stallion.

Exposure usually results in temporary infertility, and some mares become chronically infected and remain carriers of the disease causing organism for several months. First reported in England in 1977, the disease is active in several countries, including France, Germany, Japan, Belgium, Denmark, Italy, Netherlands, Norway, Sweden, Switzerland, Australia, and Czechoslovakia, but has essentially been eradicated in the United States.

The first indication of infection is short-cycling and a return to estrus. Most mares will not conceive when infected at the time of breeding, and if the mare does conceive, the fetus may be aborted or an infected foal brought to term.

The disease is naturally transmitted by coitus, but may also be transmitted indirectly through use of contaminated instruments and equipment.


  • Mild to heavy discharge from the vulva resulting from inflammation of the uterus 10 to 14 days post breeding
  • Return to estrus after a shortened cycle
  • Presence of lesions in the uterus


Contagious equine metritis is caused by Taylorella equigenitalis, a microaerophilic gram-negative coccobacillus. Two strains exist, one sensitive and the other resistant to streptomycin. Horses are the only species infected naturally by this organism, although donkeys have been infected under experimental conditions.


Because of infections in carrier mares that have no symptoms, the disease is difficult to control. Since one stallion can infect many mares, it is necessary to test suspect carrier mares bacteriologically to ensure that they are not carrying CEM.

Serologic testing will help detect mares that have previously been exposed. Taking steps to quarantine and treat infected animals is extremely important. Since contagious equine metritis has been eradicated in the United States, any horses coming into the country must meet the regulations for testing and have a health certificate issued by a full-time salaried veterinary officer of the country. The horse must also have been in that country for at least 60 days preceding shipment to the United States.

Having a thorough infectious disease prevention program in place is important in maintaining infection-free mares. Potential carrier mares should be tested before being bred to stallions.

Careful sterilization of all equipment should be done between use with each horse. Most common disinfectants, including nonionic detergents and sodium hypochlorate (30 ml of household bleach in 1 gallon of water) are effective.


Infected animals should be treated with systemic antibiotics and disinfectant washing of the clitoral area. Surgical excision of the clitoral sinuses can eliminate the organism in carrier mares.

After the initial infection has cleared, the external genitalia, including the vulva and clitoris of the mare can be cleaned with disinfectant and topical antibiotics. Some veterinarians recommend that these areas should be scrubbed for approximately two minutes with chlorhexidine surgical scrub once a day for five days.

To prevent irritation of sensitive mucous membranes, all the chlorhexidine scrub must be rinsed away with warm water. A nitrofurazone-containing ointment should be placed over the area. This treatment should be used sparingly to prevent destruction of normal flora.

In some cases, surgical removal of the clitoral sinuses may be necessary to rid the mare of the infection.

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EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.