Why are horses bred so selectively?

Selective breeding of horses is used to maintain and improve breeds of horses for specific purposes. Selective breeding is especially stringent in thoroughbred horses intended for racing, mainly due to the potential for profit if a horse is a strong competitor.

Stringent selective breeding maintains and strengthens the genetics underlying a specific horse breed, such as a thoroughbred racing horse or a Shetland pony. In the case of racing horses, owners hope that by selecting the best possible pairs of parents for mating that the resultant offspring will be strong racing horses, while pony breeders breed pony to pony to maintain a recognizable and distinct breed of animal.