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.

Mares are referred to as being in one of two groups: “resistant” and “susceptible.” As you might guess, resistant mares are normal, and the susceptible mares have delayed uterine clearance (DUC), with greater than 2 centimeters of fluid in the uterus when checked on ultrasound 24 hours after breeding.

Bradecamp focused on management techniques that can improve fertility in DUC mares and modulate the inflammatory response. Knowing which of the many treatments are most appropriate and when to use them can be tricky, and it goes back to figuring out why a mare has developed uterine inflammation.

If you know the mare is likely to have this problem, you can address it early, with a goal of prevention. Only breed her once per cycle. And consider treatment with systemic corticosteroids, such as dexamethasone, prior to breeding.

But often the veterinarian discovers the situation 24 hours after breeding. At that point, he or she is “behind the eight ball,” and the focus is on reducing the inflammation that has already occurred. Bradecamp said if she had one treatment available to remove inflammatory debris from the uterus, it would be lavage. The question of how many liters of fluid to put into the uterus and how many times to repeat the lavage depends on the mare. The bottom line is to lavage until the effluent (liquid coming out of the uterus) is clear.

Then it’s time for an ecbolic, such as oxytocin or cloprostenol, to help the uterus push the remaining fluid out. In some mares additional therapies might be necessary.

Bradecamp says the veterinarian’s best shot at a good outcome is to stay “ahead of the eight ball.” If the mare has a known problem, treat her prior to breeding. And upon discovering a problem 24 hours after breeding, lavage and help her get that inflammation out, to improve her chances of becoming pregnant that cycle.