A stallion in Wisconsin has become positive stallion No. 23 in an ongoing investigation into contagious equine metritis (CEM).

Wisconsin State Veterinarian Robert Ehlenfeldt, DVM, said this horse is considered part of the outbreak that was first discovered in 2008 because he has the same strain of causative bacterium Taylorella equigenitalis as the other horses associated with that investigation.

He said the horse was probably exposed to T. equigenitalis during collection at a Wisconsin artificial insemination station in 2008, but was just recently identified because the owner did not want the animal to be tested.

"He has been under quarantine for an extensive period with an owner who was reluctant to test him," Ehlenfeldt explained