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Thoroughbred Breed Description

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Breed Organization

The Jockey Club

Native Country

Other Names

Adult Height
15.2 - 17h

Adult Weight

General Description

The Thoroughbred stands a little over 16 hands on average and its appearance reveals its Arabian ancestry. A refined head with widely-spaced, intelligent eyes sits on a neck which is somewhat longer and lighter than in other breeds. The withers are high and well defined, leading to an evenly curved back. The shoulder is deep, well-muscled and extremely sloped while the heart girth is deep and relatively narrow. The legs are clean and long with pronounced tendons and move smoothly in unison through one plane. The bone structure of the upper hind leg makes room for long, strong muscling. The thighbone is long and the angle it makes with the hipbone is wide. The powerful muscling of the hip and thigh continues to the gaskin that is set low. Coat colors in Thoroughbreds may be bay, dark bay, chestnut, black or gray; roans are seen only rarely. White markings are frequently seen on both the face and legs.


The term Thoroughbred describes a breed of horse whose ancestry traces back to three foundation sires -- the Darley Arabian, the Godolphin Arabian and the Byerly Turk. Named after their respective owners -- Thomas Darley, Lord Godolphin and Captain Robert Byerly -- these three stallions were brought to England from the Mediterranean Middle East around the turn of the 17th century and bred to the stronger, but less precocious, native horse. The result was an animal that could carry weight with sustained speed over extended distances, qualities which brought a new dimension to the burgeoning, aristocratically supported, sport of horse racing.

So began a selective breeding process which has been going on for more than 300 years, breeding the best stallions to the best mares, with the proof of superiority and excellence being established on the race track. Key to this selective breeding process is the integrity of the breed's records. In early days, Thoroughbred breeding records were sparse and frequently incomplete, it being the custom, among other things, not to name a horse until it had proved outstanding ability. It was left to James Weatherby, through his own research and by consolidation of a number of privately kept pedigree records, to publish the first volume of the General Stud Book.

He did this in 1791, listing the pedigrees of 387 mares, each of which could be traced back to Eclipse, a direct descendent of the Darley Arabian; Matchem, a grandson of the Godolphin Arabian; and Herod, whose great-great grandsire was the Byerly Turk. The General Stud Book is still published in England by Weatherby and Sons, Secretaries to the English Jockey Club.

Several years later, as racing proliferated in the fast-expanding continent of North America, the need for a pedigree registry of American-bred Thoroughbreds, similar to the General Stud Book, became apparent. Col. Sanders D. Bruce, a Kentuckian who had spent almost a lifetime researching the pedigrees of American Thoroughbreds, published the first volume of The American StudBook in 1873. Bruce closely followed the pattern of the first General Stud Book, producing six volumes of the register until 1896, when the project was taken over by The Jockey Club.

Integrity of The American Stud Book is the foundation on which all Thoroughbred racing in North America depends. Without assurance, beyond all reasonable doubt, of the identity of every Thoroughbred which competes, or which is bred with a view to continuing the breed, the sport of racing as it is known today, could not exist. Nor would there be any possibility of measuring results of the centuries-old quest to improve the Thoroughbred.

When The Jockey Club published its first volume of the studbook the foal crop was about 3,000. By 1986 it exceeded 51,000. The Jockey Club embraced new computer technology to meet the registration challenges posed by such large numbers. Today, The Jockey Club manages one of the most sophisticated computer operations in the country. Its database holds the names of more than 3 million horses on a master pedigree file, names that trace back to the late 1800's. The system also handles daily results of every Thoroughbred race in North America, as well as processing electronically transmitted pedigree and racing data from England, Ireland, France, Australia, Japan and other leading Thoroughbred racing countries around the world.

Further giant strides in improvement of the integrity of the Stud Book came in 1977, when The Jockey Club, taking advantage of medical science advances, took the first steps of an extensive blood-typing program. From the late 1970s through 2000, every Thoroughbred foal registered in The American Stud Book, and its sire and dame, was blood-typed to insure parentage verification. Beginning with the foal crop of the year 2001, The Jockey Club replaced conventional blood-typing with DNA typing using mane hair for parentage verification. In addition to the non-invasive sample collection procedure, DNA-based parentage verification provides an efficacy of 99.9 percent, as compared to 97 percent for blood-typing.

Although there are records of horse racing on Long Island as far back as 1665, the introduction of organized Thoroughbred racing to North America is traditionally credited to Governor Samuel Ogle of Maryland, who first staged a Thoroughbred race "in the English style" at Annapolis in 1745.

As America developed so did Thoroughbred racing, spreading across the nation from coast to coast until today the volume of racing in America far outweighs that of any other country in the world. American bloodlines, too, have come to be respected in the four corners of the earth.

What began as a pastime and sporting amusement for the wealthy has now become a worldwide multi-million dollar industry whose economic impact is widely felt at regional and national levels. From license fees and direct taxes on pari-mutuel handle Thoroughbred racing generates nearly $500 million in government revenue each year. But this is relatively minor in comparison to the overall urban and rural economic contribution made by the wide and varied infrastructure of the racing and breeding industry as a whole.

A recent estimate, for example, put the industry's contribution to the economy of New York State alone at more than $1.8 billion each year.

Responding to the aberration of mid-1980's astronomic yearling prices which were fueled by European and Middle East racing interests, the annual North American Thoroughbred foal crop peaked at 51,293 in 1986. The decade was to show an overall production increase of 65% on the aggregate crops of the 1970's. But adjustments were inevitable and the foal crop has decreased each year through 1995. This necessary adjustment has more than served its purpose and a rational and more stable breeding industry has enjoyed controlled growth since.

The Thoroughbred is one of the most brilliant and versatile horses bred in the world today. Noted for its ability to carry speed over extended distances, the Thoroughbred is also a popular choice among horsemen in many disciplines beyond the race track, including hunting, jumping, eventing and polo. The Thoroughbred has been used to create new breeds of horses and to upgrade others. The key to the Thoroughbred's greatness is its speed and endurance, for which it has been bred for over 300 years.


Very highstrung. Not recommended for beginners or intermediate horse owners.


In addition to racing, Thoroughbreds compete in eventing, show jumping and dressage at the highest levels of international competition, including the Olympics. They are also used as show hunters, steeplechasers, and in western riding speed events such as barrel racing. Mounted police divisions employ them in non-competitive work, and recreational riders also use them. Thoroughbreds are one of the most common breeds for use in polo in the United States. They are often seen in the fox hunting field as well.


Although Thoroughbreds are seen in the hunter-jumper world and in other disciplines, modern Thoroughbreds are primarily bred for speed, and racehorses have a very high rate of accidents as well as other health problems.

One tenth of all Thoroughbreds suffer orthopedic problems, including fractures. Current estimates indicate that there are 1.5 career-ending breakdowns for every 1,000 horses starting a race in the United States, an average of two horses per day. The State of California reported a particularly high rate of injury, 3.5 per 1000 starts. Other countries report lower rates of injury, with the United Kingdom having 0.9 injuries/1,000 starts (1990–1999) and the courses in Victoria, Australia producing a rate of 0.44 injuries/1,000 starts (1989–2004). Thoroughbreds also have other health concerns, including a majority of animals who are prone to bleeding from the lungs (exercise induced pulmonary hemorrhage), 10% with low fertility, and 5% with abnormally small hearts. Thoroughbreds also tend to have smaller hooves relative to their body mass than other breeds, with thin soles and walls and a lack of cartilage mass, which contributes to foot soreness, the most common source of lameness in racehorses.

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