It’s a scenario that many veterinarians face throughout their career: Nearly every veterinarian in the area has tried to get this mare pregnant to no avail, and now it’s their turn. Perhaps they wonder, "Where do I start? What approach do I take? Can I help them?”

This situation is not so unusual and is similar to the case Margo Macpherson, DVM, MS, Dipl. ACT, from the University of Florida’s College of Veterinary Medicine, described during her in-depth interactive session at the 2015 Annual Convention of the American Association of Equine Practitioners, held Dec. 5-9 in Las Vegas.

“An owner approached me, asking to breed her ‘problem’ mare using artificial insemination, and due to costs I could only breed her once,” said Macpherson, setting the stage for her presentation.

In preparation, Macpherson mentally ran down the list of causes of poor pregnancy rates: fibrosis (scarring) of the reproductive tract, poor semen quality, timing of insemination, and, of course, endometritis.

“Endometritis, or inflammation of the inner lining of the uterus called the endometrium, is the No. 1 reason for poor pregnancy rates in mares,” explained Macpherson. “Endometritis can occur due to bacterial infection or, more commonly, as a side effect of breeding.”

Sperm cells promote inflammation in the uterus of all mares. Most mares are able to resolve the inflammation shortly after the breeding process; however, some mares have a prolonged inflammatory response after breeding—a condition called post-mating induced endometritis (PMIE).