You’re preparing your mare for the upcoming breeding season. The stud owner insists on a bacterial culture of your mare’s uterus prior to live breeding to reduce the chances of her passing any sexually transmitted diseases (STDs) she might have to the stallion. But what about the stallion? The mare has a higher risk of contracting an STD from the stallion than vice versa. With some STDs, the stallion is merely a carrier and exhibits no clinical signs of disease. It’s not until the mare becomes infected that the culprit stallion is identified as the source of venereal disease. Some STDs can even be transmitted in cooled fresh or frozen semen.

When a mare contracts an STD, trouble can follow in the form of a lost breeding season, lost pregnancy, or a sick (and sometimes lost) neonatal foal. The worst-case scenario is when STDs spread through a breeding farm, shutting down the farm for the entire season. Or worse yet, the disease is spread to an entire equine breeding community, resulting in tremendous economic losses!

Fortunately, the number of sexually transmitted diseases is low, and owners are becoming wiser about what venereal diseases are out there and how to reduce the risk of their transmission. A.C. Asbury, DVM, Dipl. ACT, Professor Emeritus of the University of Florida and consultant to the Grayson-Jockey Club Research Foundation; and Beverly J. Purswell, DVM, PhD, Dipl. ACT, a professor of theriogenology in the Department of Large Animal Clinical Sciences at Virginia-Maryland Regional College of Veterinary Medicine, discuss the STDs you should be aware of.

Contagious Equine Metritis (CEM)

“Contagious equine metritis is a highly contagious bacterial infection caused by the organism Taylorella equigenitalis,” says Purswell. “It hit the United States in the late ’70s from Europe. The stallion is a carrier only; it does not affect him, but he passes the bacter