Endometritis is inflammation of the endometrium, or uterine lining. It has been described as the third-most important clinical problem in equine practice after colic and respiratory tract disorders. It can be divided into four categories, which we will discuss individually.

Persistent Mating-Induced Endometritis

Transient inflammation is a normal physiological response to breeding. Normal, fertile mares clear inflammation from their uterus within 12 hours of insult, whereas mares susceptible to persistent post-mating endometritis have an intrinsic inability to evacuate uterine contents following breeding. This prolonged uterine inflammation ultimately leads to inability to conceive or early embryonic loss.

Mares that have had numerous foals or are older than 14 with poor perineal conformation are most prone to persistent post-mating endometritis. A maiden mare might develop endometritis because her cervix does not open suf?ciently during estrus. The principal clinical sign is fluid accumulation within the uterine lumen 24-48 hours after breeding, identified on transrectal ultrasound or manifested as a uterine discharge noted at the vulva lips or along the back of the hind legs. Veterinarians might also make a presumptive diagnosis based on patient history