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The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed. Thoroughbreds are considered "hot-blooded" horses, known for their agility, speed and spirit.
The Thoroughbred as it is known today was developed in 17th- and 18th-century England, when native mares were crossbred with imported Oriental stallions of Arabian, Barb, and Turkoman breeding. All modern Thoroughbreds can trace their pedigrees to three stallions originally imported into England in the 17th century and 18th century, and to a larger number of foundation mares of mostly English breeding. During the 18th and 19th centuries, the Thoroughbred breed spread throughout the world; they were imported into North America starting in 1730 and into Australia, Europe, Japan and South America during the 19th century. Millions of Thoroughbreds exist today, and more than 118,000 foals are registered each year worldwide.
Thoroughbreds are used mainly for racing, but are also bred for other riding disciplines such as show jumping, combined training, dressage, polo, and fox hunting. They are also commonly crossbred to create new breeds or to improve existing ones, and have been influential in the creation of the Quarter Horse, Standardbred, Anglo-Arabian, and various warmblood breeds.
Thoroughbred racehorses perform with maximum exertion, which has resulted in high accident rates and health problems such as bleeding from the lungs, low fertility, abnormally small hearts and a small hoof to body mass ratio. There are several theories for the reasons behind the prevalence of accidents and health problems in the Thoroughbred breed, and research continues.