Horse breeding is a business full of rewards and disappointments. Breeders eagerly await the birth of a healthy foal, but they also understand the risk of abortion or of a mare not conceiving.

To better help owners/breeders and veterinarians work together to achieve a successful breeding outcome, Christine Aurich, DVM, PhD, Dipl. ECAR, professor at the Centre for Artificial Insemination and Embryo Transfer and Graf Lehndorff Institute for Equine Science at the University of Veterinary Sciences in Vienna, Austria, recently composed a comprehensive report about mares’ reproductive cyclesinformation first-time and experienced breeders alike can use in their programs.

The mare’s reproductive cycle comprises the recurring physiologic changes prompted by reproductive hormones. When the mare is "in heat" she’s in estrus, which means she’s sexually receptive and easier to impregnate. She is in anestrus when the sexual cycle is not active; the mare is thus difficult or impossible to impregnate. The latter is induced by season (mares usually are in anestrus through the winter and early spring), pregnancy, and age (very young and older mares will likely remain in a period of anestrus), among other factors.

Once a mare is in estrus, the breeder should solicit the help of a reproduction veterinarian to monitor the mare closely for ovulation. Aurich explained that the foundation of a good reproductive program starts with a "veterinarian that has good knowledge of equine reproductive physiology and is experienced in managing mares during es