American Quarter Horse, one of the oldest recognized breeds of horses in the United States. The breed originated about the 1660s as a cross between native horses of Spanish origin used by the earliest colonists and English horses imported to Virginia from about 1610. By the late 17th century, these horses were being raced successfully over quarter-mile courses in Rhode Island and Virginia, and hence received the name Quarter Horses. The Quarter Horse was bred for performance and had considerable Thoroughbred blood as well as traits of other lines. Important sires include Janus, an English Thoroughbred imported to Virginia in 1756; Steel Dust (b. 1843); and Peter McCue (b. 1895), called the most influential sire in improving the breed.

In the early 19th century, Quarter Horses were overshadowed by Thoroughbreds, which ran better over longer distances. But Quarter Horses soon found a new acceptance in the western and southwestern United States as stock horses. The breed’s inherent quickness and agility made it ideally suited to the tasks of the developing frontier. Its good-natured disposition and natural cow-sense made the American Quarter Horse a favourite mount among cowboys during the open-range era of the West.

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Modern American Quarter Horses are short and stocky, with heavy muscular development; short, wide heads; and deep, broad chests. Since these horses are used to cut cattle from herds (see photograph), fast starting, turning, and stopping ability (see photograph) and speed for short distances are essential qualities. Their colours are variable, but all are solid. The height of mature animals varies from 14.3 to 16 hands (about 57 to 64 inches, or 145 to 163 cm), and their weight varies from 950 to 1,200 pounds (431 to 544 kg). They have a calm, cooperative temperament.

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For years little attempt was made to develop a distinct breed. In 1940, however, the American Quarter Horse Association (AQHA) was organized, and in 1950 it was reorganized to include other Quarter Horse organizations. The AQHA controls the American Quarter Horse Stud Book and Registry. With more than 2.5 million horses registered in its stud book by the late 20th century, the AQHA was the largest horse breeders’ organization in the world.