Contagious equine metritis (CEM) is a sexually transmitted bacterial infection in horses caused by Taylorella equigenitalis, primarily affecting breeding mares and stallions. While stallions typically show no symptoms, mares may exhibit mild vaginal discharge or be asymptomatic carriers, posing a risk of spreading the disease. CEM is a reportable foreign animal disease in the U.S., where strict testing, quarantine, and sanitation protocols are enforced to prevent outbreaks, especially in imported horses and breeding programs.

Diagnosis involves specific testing, and treatment consists of a five-day course of topical antibiotics under veterinary supervision, followed by retesting to confirm clearance. Once treated, horses usually recover without long-term fertility issues. Prevention focuses on annual testing of stallions, thorough breeding records, proper hygiene during breeding procedures, and immediate veterinary consultation if symptoms or fertility problems arise.