By 1908 the number of tracks had plummeted to just 25. That same year, however, the introduction of pari-mutuel betting for the Kentucky Derby signaled a turnaround for the sport. More tracks opened as many state legislatures agreed to legalize pari-mutuel betting in exchange for a share of the money wagered. At the end of World War I, prosperity and great horses like Man o' War brought spectators flocking to racetracks. During the late 1980s, another significant decline occurred, however.
Thoroughbred tracks exist in about half the states.
State racing commissions have sole authority to license participants and grant racing dates, while sharing the appointment of racing officials and the supervision of racing rules with the Jockey Club. The Jockey Club retains authority over the breeding of Thoroughbreds. Although science has been unable to come up with any breeding system that guarantees the birth of a champion, breeders over the centuries have produced an increasingly higher percentage of Thoroughbreds who are successful on the racetrack by following two basic principles. The first is that Thoroughbreds with superior racing ability are more likely to produce offspring with superior racing ability. The second is that horses with certain pedigrees are more likely to pass along their racing ability to their offspring.