Every mare has an inflammatory response to clear bacteria and debris from her uterus after being bred. Normally that inflammation peaks approximately 6 to 12 hours after mating, and it resolves within 48 hours.

But about 15% of mares develop persistent mating-induced endometritis (PMIE), or inflammation of the uterine lining, defined as the failure of the normal physiologic inflammation that occurs post-mating to resolve within 36 to 48 hours. This is a big deal because PMIE results in lower pregnancy rates and increased early embryonic losses.

At the 2016 American Association of Equine Practitioners convention, held Dec. 3-7 in Orlando, Florida, Etta Bradecamp, DVM, Dipl. ACT, ABVP, a reproductive specialist from the Rood & Riddle Equine Hospital, in Lexington, Kentucky, explained the causes and best line of treatment for these PMIE mares.

Bradecamp said PMIE has several possible causes or combinations of causes. Sometimes the mare can’t “turn off” the inflammatory response. Sometimes the uterus can’t move the inflammation out. Sometimes the dilation of the cervix is poor, as in the case of aged maiden mares, mares that have had repeated embryo flushes over several years, or mares that have experienced cervical trauma or fibrosis (scarring). Sometimes the uterus doesn’t contract well enough, so fluid accumulates. And sometimes it’s a combination of those factors