Thoroughbred
The Thoroughbred is a horse breed developed in 18th century England when English mares were bred with imported Arabian stallions to create a distance racer. Also, "thoroughbred" is an adjective often used by laymen to describe fully-blooded descendants of a particular breed.
The typical Thoroughbred stands 16 hands (64 inches/1.63 m) high, and is bay, brown, chestnut, black or gray/roan in color. The face and lower legs may be marked with white, but white will generally not appear on the body (although certain color genes, usually found in chestnuts, result in white hairs and white patches in the coat—the study of color genetics in horses is an in-depth one).
All modern Thoroughbreds descend from three stallions imported to England from the Middle East in the late 17th and early 18th centuries: the Darley Arabian, the Godolphin Arabian, also known as the Godolphin Barb, and the Byerly Turk, together with around 35 mares. (The first part of these stallions' names refers to the stallion's British owner, the second part is an indicator of the horse's origin.)
Although the Thoroughbred is primarily bred for racing, the breed is also used for show jumping and combined training due to its athleticism, and many retired race horses become fine family riding horses, endurance horses, dressage horses, and youth show horses. The larger horses are sought after for hunter/jumper and dressage competitions, whereas the smaller horses are in demand as polo ponies.
The Thoroughbred is bred primarily for racing under saddle at the gallop. Some families of Thoroughbreds are known primarily as sprinters or as distance runners.
Buyers generally select for larger individuals. Longfellow, Man O' War, Secretariat, Phar Lap, Dr. Fager, Silky Sullivan and Forego were famous, big horses, but a substantial number of famous race horses have been small. Aristides, the winner of the first Kentucky Derby was small. Roamer, Round Table, Seabiscuit, Northern Dancer, and more recently, Dalakhani and Smarty Jones, were famous, smaller horses.
Many experts who purchase Thoroughbreds attempt to assess a young horse's potential by observing its overall structural balance, the athleticism and willingness of its walk, the perceived intelligence of its outlook, and the correct conformation of its legs. Buyers of more expensive horses often hire veterinary experts to examine and report on the condition of the horse's breathing apparatus, soundness of bone structure, and size of heart.
Thoroughbreds that are born in the Northern Hemisphere technically become a year older on January first; those born in the Southern Hemisphere turn one on August first. These artificial dates have been set to enable the standardization of races for horses in certain age groups.