Horse breeding is big business, and the key to any successful breeding program lies in health care of both mares and stallions. The science of equine reproduction, also known as theriogenology, has advanced enormously in the recent years, and maintaining genetic diversity is an important principal that equine reproduction veterinarians adhere to. Dr. Juan Samper, an equine reproduction specialist, will discuss some of the issues faced by horse owners who wish to breed their animals, whether household pets or valuable performance horses, and what veterinarians charged with maintaining optimal reproductive health, must always keep in mind.