A British stallion racehorse. Thoroughbreds are lithe, supple, and built for distance. Ron Mesaros

The Jockey Club

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Lexington, Kentucky 40503

The Thoroughbred is a brilliant and versatile breed, renowned for its ability to carry speed over a variety of distances. Although primarily associated with racing, the Thoroughbred is also popular and ideally suited for many disciplines beyond the racetrack. With courage, determination, and will, coupled with fluid coordination and balance, the Thoroughbred is highly prized by horse people in the non-racing Olympic equestrian disciplines of eventing, show jumping, and dressage. The breed also makes ideal hunters, polo mounts, police horses, and recreational horses. Due to its physical prowess, the Thoroughbred has been used to create new breeds and upgrade others, but its forte has always been racing and athletic performance.

Editors Note: The Principal Rules and Requirements of The American Stud Book contains the official rules for Thoroughbred breeding and registration in North America. The Jockey Club recommends that owners and breeders consult the online edition of The Principal Rules and Requirements of The American Stud Book, available at, for the most current rules of the stud book.


The Thoroughbred’s ancestry traces back more than three hundred years to three foundation stallions—the Darley Arabian, the Godolphin Arabian, and the Byerly Turk. Named for their respective owners, Thomas Darley, Lord Godolphin, and Capt. Robert Byerley, these stallions were imported to England in the late 1600s and early 1700s. Ancestry of all Thoroughbreds today can be traced through the male line to one or more of these three Arabian stallions that lived more than two centuries ago.

The Byerly Turk lived from 1680 to 1696. At the siege of Buda in Hungary, Captain Byerley captured him from the Turks, and the horse became known as the Byerly Turk. In spite of his name, he was probably an Arabian. Captain Byerley reportedly rode the stallion at the Battle of the Boyne in 1690 and later brought him to Britain. Although not bred to many mares, he distinguished himself as a sire and carried the captain’s name into Thoroughbred history. (Due to a printer’s error, the Byerly Turk’s name was registered in the General Stud Book without the final “e.”) The Byerly Turk founded a line of Thoroughbreds, the most distinguished of which was Herod, a descendant that proved to be a very successful sire himself.

The Darley Arabian lived from 1700 to 1733. He was bought by Thomas Darley in Aleppo, Syria, in 1704. He was the second of the three foundation stallions to be imported to England, being sent by Darley from Syria to Yorkshire, England, where he was bred to numerous mares. The most successful matings were with Betty Leeds, which resulted in two very important colts, Flying Childers and Bartlet’s Childers. Approximately 90 percent of all Thoroughbreds today are descended through Flying Childers and his great-great grandson, Eclipse. As such, the Darley Arabian is the most important of the three foundation stallions in terms of his lasting influence on the Thoroughbred breed.

The Godolphin Arabian (also called Barb) lived from 1724 to 1753. He was foaled in Yemen and given by the Bey of Tunis to the king of France as a gift. Apparently something went amiss, as one story tells of the horse being relegated to pulling a lowly water cart in Paris. The carthorse was admired and bought by an Englishman named Edward Coke, who brought him to England. Coke subsequently presented him to the Earl of Godolphin, at whose stud he was bred to several distinguished mares. He sired the champion mare Aelima, that was imported to Maryland in 1750. Mated to the mare, Roxana, the Godolphin Arabian sired Lath, the greatest racehorse in England after Flying Childers. Another mating of these two produced Cade, the sire of the great Matchem that carried on the line of the Godolphin Arabian. In 1850, it was remarked that “the blood of the Godolphin Arabian is in every stable in England.”

Out of some two hundred Oriental horses imported to England between 1660 and 1750, only the direct descendants of these three foundation stallions contributed to the Thoroughbred’s greatness. All three originated in the Middle East and were bred to Britain’s native sprinting mares, which were very probably Scottish Galloways, with the resultant foals being the first Thoroughbreds, per se. The breed was noticed for its ability to carry weight with sustained speed over extended distances. These qualities brought a new dimension to horse racing, a sport then supported by the burgeoning English aristocracy. So began a selective process of breeding the best stallions to the best mares, with the proof of superiority and excellence being established on the racetrack.

Descendents of Foundation Stallions

Although the three Arabian sires were the progenitors of the Thoroughbred as it is known today, a number of generations were required to create horses that could consistently pass on the distinguishing characteristics of the breed.

Herod: A descendent that fixed the influence of the Byerly Turk as a foundation sire was Herod, foaled in 1758. He was owned by the Duke of Cumberland, the third son of King George II, who was an important breeder of horses at Newmarket and in Hanover. Although Herod was not an outstanding racehorse, he did prove to be a superlative sire. His descendants were extremely important in the development of the Thoroughbred throughout Europe and North America.


Fillies at a morning workout. Thoroughbreds have great stamina and courage. Darlene Wohlart/

Eclipse: In 1764, there was a great eclipse, and this astronomical event became the name of the horse that would become a star in the history of the Thoroughbred. Eclipse began racing in 1769 at age five and ran away from the competition in his first race at Epsom. It was at this race where the famous Denis O’Kelly remarked, “Eclipse first, the rest nowhere.” Eclipse won eighteen races in his career and was never whipped or spurred. The list of Eclipse’s distinguished descendants is virtually endless, and he is the reason for the predominance of the Darley Arabian line over the other two foundation stallions’ lines.

Matchem: Most racehorses are noted for their speed, but speed sometimes comes at the price of an excitable temperament, yet this was not the case with the horse Matchem. Foaled in 1748, he was the grandson of the Godolphin Arabian. Besides speed, he passed on an excellent disposition. The horse, Snap, a grandson of the Darley Arabian, was compared to the gentle Matchem: “Snap for speed and Matchem for truth and daylight.” When considering Matchem’s blood heirs, there can be found many even-tempered, yet fast horses. Matchem’s offspring had a particular influence on American horses after his owner’s son, Edward Fenwick, immigrated to South Carolina in 1755 and brought ten of Matchem’s descendants to America. Brutus, one of Matchem’s sons, dominated racing in South Carolina for some time.


The Thoroughbred is a bold horse with a refined head and intelligent eyes. Kay Holloway

Significant American Thoroughbreds

Bulle Rock: An event of central importance in the history of American horseracing was the importation of Bulle Rock to Virginia in 1730 by Samuel Gist. A son of the Darley Arabian, Bulle Rock is remembered as the first Thoroughbred to reach U.S. shores. He was twenty-one years old when he arrived and had been a successful racehorse in Britain in his youth. By 1800, Bulle Rock had been followed by a succession of 338 other imported Thoroughbreds.

Monkey, Janus, and Fearnought: Of the sixty-three identifiable Thoroughbred imports before the American Revolution, the most important were Monkey, Janus, and Fearnought. Monkey was imported in 1747 at the age of twenty-two and sired some three hundred colts in Virginia. Janus was imported as a ten-year-old by Mordecai Booth in 1756 and had a profound influence on the Quarter Horse. John Baylor imported Fearnought in 1756 as a nine-year-old. Fearnought had a stud fee that was five times the amount charged for other good sires and was the most important Thoroughbred sire in the United States until Diomed.

Diomed: Among the most important horses imported after the American Revolution was Diomed, foaled in 1777. A great racehorse in his youth, he was the winner of the first Epson Derby in England in 1780, but his career later floundered. An American, Col, John Hoomes, bought him in 1798 and Diomed sired some of the most famous horses in American turf history, including Sir Archie.

Messenger: In May 1788, another Thorough-bred was imported from England that put his stamp on the future of American racing. This horse was Messenger, and he first stood at stud in Philadelphia. After having been sold to Henry Astor of New York and later to Cornelius Van Ranst, he sired a number of superior racehorses. His greatest descendant was Rysdyk’s Hambletonian, his great-grandson that became the foundation sire of the Standardbred breed.

Sir Archie: Sir Archie became a singularly important influence in Thoroughbred history. Foaled in Virginia, he became what most experts consider to be the first great Thoroughbred stallion bred in America. At the age of four, he became one of the greatest runners of his day, excelling in four mile heats. William Ransom Johnson, the “Napoleon of the Turf,” once owned Sir Archie and described him as “the best horse I ever saw.” After no more challengers could be found, Sir Archie’s racing career ended and he went to stud. In twenty-three years at stud from 1833, he sired many magnificent horses and was also the great grandsire of Lexington.

Lexington: Foaled in 1850, Lexington was a United States champion race horse who became the most successful sire during the second half of the nineteenth century. Lexington became the leading sire in North America sixteen times. Nine of the first fifteen Travers Stakes were won by one of his sons or daughters. Lexington sired three Preakness Stakes winners and also sired Cincinnati, General Ulysses S. Grant’s favorite horse. Cincinnati was depicted in numerous statues of Grant that remain to this day. Lexington was part of the first group of horses inducted into the National Museum of Racing and Hall of Fame in 1955. The Belmont Lexington Stakes runs every year at Belmont Park in honor of Lexington, as does the Lexington Stakes at Keeneland Race Course.

U.S. Racing History

Although there are records of horseracing 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, at whose behest racing “between pedigreed horses in the English style” was first staged at Annapolis in 1745.

As the United States developed, so did Thoroughbred racing, spreading across the nation from coast to coast. Today, the volume of racing in the United States far outweighs that of any other country, and American bloodlines are the most sought after in the world.

What began as a pastime and sporting amusment for the wealthy has now become a worldwide multibillion dollar industry whose economic impact is widely felt at regional and national levels. According to the study entitled, “The Economic Impact of the Horse Industry on the United States,” issued in 2005 by Deloitte Consulting, the Thoroughbred industry in the United States has a $33.6 billion total effect on the gross domestic product (GDP) and creates over five hundred thousand fulltime jobs.


With Thoroughbreds pounding down the stretch, racing is the most popular test of equine speed and a great moment in sport. Although most Thoroughbreds in the Northern Hemisphere are born in the spring, regardless of the actual date, January 1 is their official birthday. The youngsters spend their formative months playing with other colts and fillies and growing in size and spirit. Some yearlings are auctioned at such places as the Keeneland Thoroughbred Racing and Sales in Lexington, Kentucky. The record price paid for a Thoroughbred yearling is more than $13 million.

Having spent its first year developing size and power, the young Thoroughbred begins training as a yearling. It learns to accept a saddle and bridle and a rider on its back, and ultimately to break from a starting gate and run around a track. Leading a horse around a training track to develop wind and muscle is called “ponying.” Whether on a farm or at a track, Thoroughbreds are galloped in morning workouts to keep them in racing trim.

Although jockeys are generally small, they must have the strength and courage necessary to guide a horse thundering down the track at top speed. Leading jockeys have quick reflexes, a finely developed sense of timing, and, above all, a mastery of turf strategy. They express “a cool hand with a hot horse.”

Jockeys sat upright until the end of the 1800s, when Tod Sloan developed the exaggerated forward-seat position. Placing the rider’s weight over the horse’s center of gravity not only greatly reduces wind resistance, but more importantly it also keeps a rider in better balance with a horse at high speeds.

To ensure that each horse will carry the precise assigned weight, jockeys and their equipment weigh out before and weigh in after a race. Weight is an ever-present factor in a jockey’s life, as few weigh more than 114 pounds, and those who have difficulty with excess poundage must diet constantly. Like coats of arms, the distinctive colors and designs on their shirts and caps, known as “silks,” are a way to identify horse and rider. The racing saddle also is small, weighing approximately two pounds. The difference between assigned weight and the rider’s actual poundage is made up by lead bars carried in saddle cloth pockets. Some types of races require more accomplished horses to carry more weight as a handicap.

Famous Races

Winning the Triple Crown race series is one of the most elusive and coveted achievements in all of sports. The Triple Crown consists of three races within a five-week span and only three-year-old horses are eligible, meaning a Thoroughbred has only one shot at winning the Triple Crown. Through 2008, only eleven horses had won the Triple Crown, with the horse Affirmed in 1978 being the last to accomplish the feat.

The first race of the Triple Crown is the Kentucky Derby held on the first Saturday in May at Churchill Downs in Louisville, Kentucky. It has been run for more than 130 years and is widely considered the premier race in the United States, with up to twenty Thoroughbreds running 1.25 miles. White carnations were the Derby’s original official flowers, but when they were not delivered in 1903, one owner’s wife made a blanket of roses; since then the race came to be known as the Run for the Roses. The stallion Secretariat set the record for the fastest time (1:59.4) when he won the Kentucky Derby in 1973.

Two weeks later is the 1.1875-mile Preakness Stakes at Pimlico Race Course in Baltimore, Maryland. The last race in the Triple Crown follows three weeks later and is the Belmont Stakes in Elmont, New York. It is dubbed the Test of the Champion, because one lap around Belmont Park’s huge 1.5-mile oval track is the longest distance most of its entrants will ever race.

In addition to the “classic” races for three-year-olds each spring, Thoroughbred racing has had a championship day since 1984, which is held in the fall and known as the Breeders’ Cup World Championships. Similar to the National Football League’s Super Bowl or Major League Baseball’s World Series, the Breeders’ Cup is North America’s richest day of racing, offering more than $25 million in prize money in fourteen championship races. National pride is also on the line because the event annually attracts many of the best horses, jockeys, and trainers from around the world.

Twentieth Century Champions

Any list of the greatest racehorses of the twentieth century must include Man O’ War. Foaled in 1917, Man O’ War is still regarded by many as the greatest of American racehorses. He finished first in all but one of his twenty-one starts, often winning in record time and by wide margins.

Count Fleet won the Triple Crown in 1943 capped by a twenty-three-length victory in the Belmont Stakes in 1948. Citation followed Whirlaway as the second Triple Crown winner for the famed Calumet Farm and, at six, became the first Thoroughbred to reach $1 million in career race earnings. Native Dancer won twenty-one of his twenty-two starts from 1952–1954, his only loss coming by just a head in the Kentucky Derby. Kelso was the only horse in history to be voted Horse of the Year five times, from 1960–1964. In 1973, Secretariat became the first horse in a quarter century to win the Triple Crown, capped by an astounding thirty-one-length victory in the Belmont Stakes. His image graced the covers of Time, Newsweek, and Sports Illustrated magazines.

Forego was awarded a record eight Eclipse Awards, including Horse of the Year and Champion Handicap Horse in 1974, 1975, and 1976, as well as Champion Sprinter in 1974.

In 1977, Seattle Slew became the first undefeated winner of the Triple Crown and was named Horse of the Year. The following year, Slew firmly established himself as one of the greatest champions of the twentieth century by defeating 1978 Triple Crown winner, Affirmed, in the Marlboro Cup Invitational Handicap in what was the first ever meeting of two Triple Crown winners.

In racing’s greatest ongoing rivalry, Affirmed and Alydar waged war through 1977 and 1978. Affirmed won seven of their ten meetings, including all three Triple Crown races, but most were extraordinarily close finishes.

In recent years, four Thoroughbreds—John Henry, Alysheba, Cigar, and Curlin—have set the all-time record for career earnings. The ultimate rags-to-riches story, John Henry dominated U.S. turf racing in the early part of the 1980s. Purchased as a yearling in 1976 for just $1,100, John Henry earned $6,597,947 on the track and was named Horse of the Year in both 1981 and 1984.

Dubbed as America’s horse after capturing the first two legs of the Triple Crown in 1987, Alysheba was named Horse of the Year in 1988 following his dramatic victory in the Breeders’ Cup Classic at Churchill Downs. He retired with earnings of $6,679,242.


Mare and foal. Thoroughbreds have been used to create and upgrade other breeds. Darlene Wohlart/

During one phase of his career over three seasons, 1994–1996, Cigar won sixteen consecutive races, matching the then modern record of Citation. He traveled to Dubai to win the inaugural running of the Dubai World Cup, and his career earnings were around $10 million.

Cigar’s earnings record stood through the conclusion of the twentieth century, but was eclipsed in 2008 by Curlin, classic winner of the Preakness Stakes and Breeders’ Cup Classic at age three, whose four-year-old season was highlighted by a dominant performance in the Dubai World Cup. Curlin retired with eleven wins from sixteen starts and earnings of $10,501,800.


Key to the selective breeding process is the integrity of the breed’s records. In early days, English Thoroughbred breeding records were sparse and frequently incomplete, it being the custom, among other things, not to name a horse until it had proven its 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 three stallions: 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.


Landscape of a Thoroughbred farm in Kentucky’s bluegrass country. Kay Holloway

Several years later, as racing proliferated in North America, the need for a pedigree registry of U.S.-bred Thoroughbreds similar to the General Stud Book became apparent. Colonel Sanders D. Bruce, a Kentuckian who had spent a lifetime researching the pedigrees of American Thoroughbreds, published the first volume of The American Stud Book in 1873. Bruce closely followed the pattern of the first General Stud Book, producing six volumes of the register until 1896, when The Jockey Club assumed responsibility for the project. The Jockey Club, a U.S. Thoroughbred organization, was established in 1894 and today is the governing body for all matters pertaining to Thoroughbred registration in North America.

When The Jockey Club published its first volume of the stud book, the foal crop was about three thousand; by 1986, it had exceeded fiftyone thousand, and these days, the annual registered foal crop encompasses approximately thirty-five thousand foals. The Jockey Club’s database holds the names of more than 4 million Thoroughbreds tracing back to the mid 1700s. The American Stud Book includes all Thoroughbreds foaled in the United States, Canada, and Puerto Rico, as well as Thoroughbreds imported into these countries from nations around the world that maintain similar Thoroughbred registries. The system also handles daily results of electronically transmitted pedigree and racing data from areas throughout North America as well as from the United Kingdom, Ireland, France, Australia, Japan, and other leading Thoroughbred racing countries around the world.

Registration Criteria

Beginning in 2001, The Jockey Club replaced conventional blood-typing with DNA typing for parentage verification as a requirement for registration in the stud book. Besides DNA typing, registration requires that a foal satisfy all of the rules for registration as set forth in the “Principal Rules and Requirements” section of The American Stud Book.

The rules require, among other things, the following:

• A foal’s pedigree authentically traces in all its lines to horses recorded in either The American Stud Book, or a foreign stud book approved by The Jockey Club and the International Stud Book Committee;

• The foal is the result of a stallion’s live, natural cover of a broodmare; and a natural gestation takes place in, and delivery is from, the body of the same broodmare in which the foal was conceived. Any foal resulting from, or produced by, the processes of artificial insemination, embryo transfer or transplant, cloning, or any other form of genetic manipulation is not eligible for registration.

When owners submit their name choices for registered foals, The Jockey Club checks each name for phonetic similarity against more than 430,000 names already in active use and for compliance with the rules of naming the horses.

Breed Characteristics

The Thoroughbred stands a little over 16 hands on average, though “average” is a key word, since there are many over or under this height.

Coat colors in Thoroughbreds may be bay, dark bay/brown, chestnut, black, gray/roan, white, or palomino. White markings are frequently seen on both the face and legs.

Conformation is based on practical application of what the Thoroughbred body is supposed to do: carry more than 1,000 pounds of body weight over a variety of distances, traveling at speeds of 35 to 40 miles per hour, and yet still have the strength and suppleness to respond to the changes of pace or direction of racing conditions.

The Thoroughbred’s Arabian ancestry is revealed in its refined head. It should be correctly proportioned to the rest of the body, displaying a good, flat forehead with widely spaced, intelligent eyes. Carried relatively low, the head sits on a neck that 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. The heart girth is deep and relatively narrow.

The legs are clean and long with pronounced tendons. From the point of the shoulder, the forearm should show adequate muscling that tapers toward a clean-looking knee, which, in turn, tapers into the full width of the cannon. The cannon should be short and comparatively flat, with tendons distinctly set out and clean. The pastern should be neither too long nor too short and should be set at an angle that is a little less than 45 degrees to the vertical. When viewed from behind or in front, the legs should be straight 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. The trailing edge of the hind cannon should follow a natural perpendicular line to the point of the buttock.

The Thoroughbred’s conformation enables it to reach speeds exceeding 40 miles per hour. Its rear legs act as springs as they bend and straighten during running. This tremendous spring power helps thrust the horse forward as its front legs provide pull. The head and long neck also help to make running smooth and rhythmic. The neck moves in unison with the forelegs, aiding the horse in its forward motion and extending the time that it literally is airborne.

Thoroughbreds are also equipped with the most athletic feet in the world. Their hooves have a unique structure that gives it built-in cushioning to withstand the equivalent of one hundred times the force of gravity on each hoof, which is the force exerted when a Thoroughbred is running at full speed.

Credit: The Jockey Club

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