The Thoroughbred breed can be traced to three
foundation sires: the Byerly Turk, the Darley Arabian, and the Godolphin
Arabian. These Arabian stallions were brought to England at the end
of 1600s and beginning of the 1700s by their owners and bred with native
English mares. The Arabians had with them stamina and speed while the native
horses were strong resulting in the Thoroughbred. Gaining from both
side of it's heritage, it can run long distances with a sustained speed.
This brought the sport of horse racing up to a new level. The
English pass time of horse racing was adopted by the developing America
and in 1730 the son of the Darley Arabian, Bulle Rock,
arrived in Virginia and is remembered as the first Thoroughbred to reach
America. Since then many more were imported to and bred in America.
This horse grew to dominate the racetrack giving birth to well known and
talented horses such as Man o'War, Seabiscuit, Ruffian, and
The average height of a Thoroughbred is 16-16.2 hands,
though they range from 14.2 to over 17 hands. The coloring of a
Thoroughbred is always solid, though white markings are sometimes
found. The most common colors are bay, chestnut, and brown but there also
is grey, black, and roan. A Thoroughbred generally has sloping
shoulders, an elegantly refined head, clean legs, and muscular
quarters. Primarily bred for racing, they are used also for show
jumping, dressage, and hunting.
You can find a lot of information about horse breeds and registration facts at that Horse Breed Associations web sites:
American Thoroughbred Horse Association: JockeyClub