A third stallion in Wisconsin has tested positive for contagious equine metritis, or CEM, a treatable reproductive disease of horses, the state’s Department of Agriculture, Trade and Consumer Protection announced Jan. 30.

The National Veterinary Services Laboratories in Ames, Iowa, reported the positive test result. The stallion, a 6-year-old Quarter Horse located in Outagamie County, has been quarantined since Jan. 20, when state animal health authorities learned he had been at a Wisconsin artificial insemination center at the same time as a previously reported infected stallion from Outagamie County.

Watch the CEM testing and treatment protocol for mares and stallions.

State and federal animal health personnel will examine the newly identified stallion’s breeding records and movement history to trace what mares might have been exposed via natural breeding or artificial insemination, and what stallions might have been exposed via shared artificial insemination equipment.

Any exposed animals, in Wisconsin or other states, will be quarantined for testing. Wisconsin owners of exposed animals will be contacted by state or federal animal health officials. For those in other states, the department will notify those states’ animal health authorities, who will contact owners.

There is no human health risk and no risk to horses in the general population.

Nationwide, the CEM investigation now involves at least 512 horses in 45 states, according to the USDA. The outbreak began in mid-December, when a Quarter Horse stallion on a Kentucky farm tested positive during routine testing for international semen shipment.

CEM is a contagious bacterial infection that passes between mares and stallions during mating. It can also be transmitted on contaminated insemination equipment. Stallions do not suffer any clinical signs, but the infection causes inflammation in the mare’s uterine lining. This can prevent pregnancy or cause the mare to abort if she becomes pregnant. The disease is treatable with disinfectants and antibiotics.

CEM is considered a foreign animal disease in the United States. It was first discovered in Europe in 1977, and has appeared in the United States only twice outside quarantine stations where stallions are required to be tested and treated before being released into the country. There was an outbreak in 1979. In 2006, three Lipizzaner stallions imported into Wisconsin from Eastern Europe tested positive after their arrival, but before they had been used for breeding.

See the USDA Animal and Plant Health Inspection Service’s CEM page.