In theory, horse breeding is simple: Mare plus stallion equals foal. However, it’s not always that straightforward. From sterile stallions to anestrus mares, reproductive veterinarians are often faced with challenging cases that require some problem-solving and subsequent treatment.

At the 2015 World Equine Veterinary Association Congress, held Oct. 8-10 in Guadalajara, Mexico, reproduction specialist Patrick McCue, DVM, PhD, Dipl. ACT, took a closer look at managing the problem mare. McCue is a professor of equine theriogenology at Colorado State University’s Equine Reproduction Laboratory, in Fort Collins.

Several scenarios can lead to a patient being labeled a “problem mare,” McCue said, including:

  • Not becoming pregnant after being bred to a fertile stallion over the course of three estrous cycles;
  • Being unable to successfully carry a foal to term;
  • Having known reproductive pathology; or
  • Having behavior issues related to reproduction.

He said it’s crucial to make an accurate diagnosis of the problem before developing a treatment and management program, and he encouraged practitioners to devise a systematic plan for evaluating problem mares.

McCue reviewed several conditions that can contribute to reproductive problems in mares.

Persistent mating-induced endometritis—One of the most common causes of reduced fertility in mares, persistent mating-induced endometritis is a chronic inflammation of the uterine wall lining after breeding or artificial insemination.

McCue said mares, especially older ones, are sometim