Q: How does test breeding of stallions assist in the diagnosis of CEM?

A: To maximize the chance of detecting CEM infection, stallions are required to be tested by both bacterial culture and test breeding. Test breeding will sometimes detect a T. equigenitalis infection that bacterial culturing of the stallion did not detect. Test breeding involves breeding a stallion to two certified CEM-negative mares. Following test breeding, the test mares are serially tested for CEM by bacterial culture and a serology test to determine if they are infected. It takes a minimum of 35 days after the test breeding to declare the stallion negative.

Of the 23 positive stallions detected during the 2009 United States CEM Outbreak Investigation, three stallions were confirmed by test breeding protocols. Difficulties in isolating the CEM organism from heavily contaminated sampling sites led to false negative cultures and the 3 stallions were only confirmed positive after the live cover test breeding.

The UC Davis Center for Equine Health maintains a herd of CEM-negative test mares specifically for the CEM quarantine program. The mares are well trained and our technicians know their personalities which helps make the process smooth for everyone. The availability of this unique test mare herd is part of the UC Davis advantage and ensures the safety and well-being of your stallion.