Breeding has long played an important role in the world of horse racing. In fact, the majority of thoroughbreds all trace back to a single broodmare, who appears in the pedigree of each of three foundation stallions. Some believe this is the best way to breed champions, and many theories and books have been written on the subject.

However, others such as the Humane Society of the United States (HSUS), argue that current practices are contributing to numerous weaknesses and defects, as well as overbreeding. According to the HSUS, the most important aspect for all breeders, whether backyard or large scale, is quality. "Breeders should plan their breeding programs in a way that enables them to properly market and train each individual horse. And, breeders should be willing to take back the horses they produce, at any time, for any reason. Similarly, breed registry organizations that make their money from registering new foals need to promote responsible breeding practices."

Artificial insemination and embryo transfer are becoming more commonly used methods, but while these practices are recognized by some horse registries, in order to be registered as a thoroughbred with The Jockey Club, a horse must be conceived via "live cover" (natural mating). There are also a number of financial incentives associated with breeding, such as stud fees and tax breaks, and of course, a thoroughbred with a winning bloodline is also thought to have a much stronger chance of ultimately bringing home numerous purses.

During the breeding season, stallions and mares ideally should receive adequate and quality hay, grain, water and supplements, along with regular veterinary checks. Unfortunately, whether or not these standards are maintained depends on the breeding facility.