Thoroughbred
Horse racing

Thoroughbred horses are primarily bred for racing under saddle at the gallop. Thoroughbreds are often known for being either distance runners or sprinters, and their conformation usually reflects what they have been bred to do. Sprinters are usually well muscled, while stayers, or distance runners, tend to be smaller and slimmer. The size of the horse is one consideration for buyers and trainers when choosing a potential racehorse. Although there have been champion racehorses of every height, from Zenyatta who stood 17.2 hands, to Man o' War and Secretariat who both stood at 16.2 hands, down to Hyperion, who was only 15.1, the best racehorses are generally of average size. Larger horses mature more slowly and have more stress on their legs and feet, predisposing them to lameness. Smaller horses are considered by some to be at a disadvantage due to their shorter stride and a tendency of other horses to bump them, especially in the starting gate. Historically, Thoroughbreds have steadily increased in size: the average height of a Thoroughbred in 1700 was about 13.3 hands high. By 1876 this had increased to 15.3.

In 2007, there were 71,959 horses who started in races in the United States, and the average Thoroughbred racehorse in the United States and Canada ran 6.33 times in that year. In Australia, there were 31,416 horses in training during 2007, and those horses started 194,066 times for A$ 375,512,579 of prize money. During 2007, in Japan, there were 23,859 horses in training and those horses started 182,614 times for A$ 857,446,268 of prize money. In Britain, the British Racing Authority states there were 8,556 horses in training for flat racing for 2007, and those horses started 60,081 times in 5,659 races.

Statistically, fewer than 50% of all race horses ever win a race, and less than 1% ever win a stakes race such as the Kentucky Derby or Epsom Derby. Any horse who has yet to win a race is known as a maiden.

Horses finished with a racing career that are not suitable for breeding purposes often become riding horses or other equine companions. A number of agencies exist to help make the transition from the racetrack to another career, or to help find retirement homes for ex-racehorses.
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