In the United States, thoroughbred racing is generally held on flat dirt roads
or grass; other tracks hold quarter-mile races, harness races, or a combination
of all three. Competitions for other breeds of horses, such as Arabians, are
less common. Thoroughbred races in the United States are held at a variety of
distances, the most common being from 4.5 miles (905 meters) to 1.5 miles (2414
meters); depending on the distance, breeders of Thoroughbred races can raise
horses by Make it win at a specific distance.(引文)
Horses are born and left to pasture. In the modern horse racing environment,
horses must be named before they can be raced. They can be raced at the age of
two and become stallions after retirement. Only a few male horses participate in
breeding, while most female horses are registered after retirement. For breeding
mare. Many horses are also slaughtered for meat.(引文)