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. As "thoroughbred" is an adjective that describes being fully-blooded descendants of a particular breed, some consider the proper name of this particular breed to be English Running Horse, as horses of different breeds can be said to be "thoroughbred" members of those breeds. It is more common, however, to use "thoroughbred" to designate horses registered by the Jockey Club of a given country, and "purebred" to refer to registered horses of any breed, as in "purebred" Morgan, "purebred" Arabian, and "purebred" Thoroughbred.
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 Goldophin 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.)
The first thoroughbred horse in the American Colonies was Bulle Rock, imported by Samuel Gist of Hanover County, Virginia, in 1730, to sire improved foals. Col. As a brood mare, Benjamin Tasker, Jr.'s "Selima," foaled at Earl Godolphin's stud April 30, 1745 and shipped to Maryland in 1750, dominated the 18th century bloodlines as her descendent, "Lexington," dominated the bloodlines of the 19th century. Though Maryland and Virginia were the centers of Colonial thoroughbred breeding, the term "thoroughbred" was first used in the United States in an advertisement in a Kentucky gazette to describe a New Jersey stallion called Pilgarlick.
In the United Kingdom, the registry for these horses is maintained by Weatherbys. A different organization (The Jockey Club) maintains the registry in the United States. There are official Jockey Club registries in many different countries. The first thoroughbred registry record, or "stud book," was the creation of a single man in England in the 18th century, and is believed to be the first invention of its kind.
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 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). A handful of non-albino Thoroughbreds have been born with white coats. For many years, The Jockey Club (USA) would not register a Thoroughbred as white; most such horses were registered as grays. However, The Jockey Club now recognizes white as a legitimate, though exceedingly rare, color.
The thoroughbred is bred primarily for racing under saddle at the gallop. There is variation in size and individual conformation (the structure and appearance of the horse), and buyers of potential race horses select them based on this conformation, their "page" (their pedigree and race record of individuals in that pedigree as printed in an auction catalog), and their overall health and soundness of wind and limb. Buyers of sprinters (horses who will race shorter distances--up to a mile) generally select a more muscular horse; those interested in training for the "classic" distances of over a mile generally select a rangier, longer legged horse. Some families of thoroughbreds are known primarily as sprinters or as distance runners, primarily as horses who prefer to race on dirt tracks, or primarily as horses who prefer turf tracks, such as those found in Europe. Buyers generally select for larger individuals (Man O' War, Secretariat, Dr. Fager, and Forego were famous, big horses), but a substantial number of famous race horses have been small (War Admiral, 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 born in the Northern Hemisphere all become technically a year older on January 1; those born in the Southern Hemisphere, on July 1. These artificial dates have been set to enable the standardization of races for horses in certain age groups.
Approximately 35,000 thoroughbred foals are registered each year in the U.S. The largest number of foals are born in Kentucky, Florida, and California. The thoroughbred industry is a huge agri-business. It supports tens of thousands of jobs in each of these states, from jockeys, trainers, starters, grooms, and kitchen employees at the race track, to farm employees assisting with the birth of foals, the grooming of yearlings, or the growing and preparation of feed, to veterinarians who understand and treat horses, to drivers of horse vans who transport horses across country, to employees of auction houses that specialize in the sale of horses, to employees of companies who develop products to improve the lives of horses and people who work with them. Wagering on races provides purses to the winners and taxes to the state. It is the State Horse of Maryland.