How Thoroughbred Horses Work

The exact age of this Thoroughbred is unknown, although we can tell you its birthday: January 1.
The exact age of this Thoroughbred is unknown, although we can tell you its birthday: January 1.

There's at least one unusual fact about Thoroughbred horses: Every Thoroughbred horse in the Northern Hemisphere has the same birthday. No matter what month a Thoroughbred is born, its birthday falls on January 1. (The universal birthday is August 1 in the Southern Hemisphere.) This makes it easier to keep track of Thoroughbred horses' bloodlines; the rule was created by the organizations dedicated to regulating the Thoroughbred breed. It also makes it easier for racing purposes. Thoroughbred races aren't open to colts (male horses under age 5) and fillies (females under age 5) until age 2, and some races, like the famed Kentucky Derby, are only open to 3-year-olds.

But this presents some problems. This means that a foal -- a newborn or nursing horse -- born on December 31 will turn one the following day [source: Snellow]. A 1-day-old 1-year-old won't have as much training and maturity and therefore won't compete as well against older horses that are considered the same age. As a result, horse buyers tend to shy away from horses born late in the year, which in turn means that horse breeders do everything they can to ensure their foals are born in the first half of the year. This has led to interventions like drugs and the use of artificial light to keep the reins tight over Thoroughbred reproduction.


This is pretty typical of the relationship with humans and Thoroughbred horses. Officials make a rule and the breed is adjusted to get the most benefit from it. It's nothing new; humans have had a hand in the reproduction of the Thoroughbred breed since its beginning, creating it through selective breeding in England just 300 years ago. In just three short centuries, the Thoroughbreds have become one of the most celebrated breeds of any animal, and the sport of modern horse racing has evolved symbiotically with it.

This has been both beneficial and costly for the Thoroughbred breed. While these horses love to race, are literally born for it, the centuries of selective breeding for faster, lighter horses has often led to tragedy on the race track. In this article we'll look at this storied and beautiful breed and how humans have shaped it, racing Thoroughbreds and the controversy around how the breed has been handled in recent years.

History of Thoroughbreds

A circa 1690 painting of the foundation sire the Byerly Turk, shortly after he was captured and kept by Robert Byerley.
A circa 1690 painting of the foundation sire the Byerly Turk, shortly after he was captured and kept by Robert Byerley.
Hulton Archive/Getty Images

It wasn't until the three stallions that make up the foundation sires of the breed arrived in England around the beginning of the 18th century that the Thoroughbred breed was born. These horses from the Oriental group -- Arabians, Turks and Barbs that are native to the Middle East -- mated with larger English mares to form the Thoroughbred. All Thoroughbred foals can trace their bloodlines directly back to one of these three foundation sires.

Horses from the Oriental group were prized in both racing horses and war by groups around the Arabian Peninsula for at least a thousand years before the foundation sires arrived in Europe [source: International Museum of the Horse]. The English mares the foundation sires bred with in the 18th century already had some Arabian in their blood; the breed was first encountered by Europeans during the Crusades in the 11th and 13th centuries and many soldiers made the trip back to Europe with horses they'd captured in the Middle East. This history of war was maintained in the Thoroughbred breed as well; the horses were used in both world wars for cavalry.


The first foundation sire arrived in England in 1688. Captain Robert Byerley captured a Turk, a breed of horse descended from the Turcoman horse, native to the Middle East, was captured in battle in Hungary [sources: Bailey, Lundberg]. Byerley admired the horse's courage in battle and brought it back to England with him, where the stallion became known as the Byerly Turk (the second "e" was lost over time) [source: Jockey Club].

In 1704, a stolen Barb, another Oriental group breed, arrived in England. The Darley Barb (also called Darley Arabian) was a 4-year-old colt purchased by Thomas Darley, a diplomat to Syria, who had purchased the horse from a Bedouin sheik. The story goes that Darley, upon finding out the sheik reneged on the purchase and failed to deliver the horse, had the Barb stolen and smuggled out of the Middle East through Turkey [source: Lundberg].

The third foundation sire, the Godolphin Arabian from Yemen, arrived rather unappreciated in England sometime after its birth in 1724. The Godolphin Arabian was part of a quartet of Arabians given as a gift to the king of France, who released them. After serving as a cart horse in Paris, the Godolphin changed hands several times before he was purchased by the Second Earl of Godolphin around 1733 [source: Lundberg].

The Thoroughbred Breed

The three foundation sires created a new breed of horse, the Thoroughbred. The Oriental group horses, particularly the Godolphin, brought quickness and agility to the breed. Arabians tend to be small horses, light and quick on their feet; Arabians have lighter bones than other breeds. Bred with the larger, slower English mares, the foundation sires produced a new breed that was both quick and muscular. The result is a breed of horse that averages 16 hands (a hand equals four inches, or about 10 centimeters, measured from the ground to the withers, a ridge just above the shoulders) in height and weighs an average of 1,000 pounds (454 kilograms) [source: Horse Hats]. It has an average lifespan of 25 years [source: WGBH].

Thoroughbreds have two unusual characteristics that make them particularly well suited for racing. Their long necks move in unison with their front legs, which propels them further forward. Second, the hind legs in the breed bend and straighten in a nearly vertical line, which produces a spring-like effect and propels the horse forward more efficiently with each step [source: Jockey Club].


The pattern of movement any animal produces with its legs is known as its gait. The Thoroughbred's gait in a full gallop is something spectacular. The average stride length of a Thoroughbred tends to be more than 20 feet (6.1 meters) [source: Horse Hats]. This means that the distance between the point where one hoof makes contact with the ground and the point where that same hoof next makes contact with the ground is as long as two average stretch limousines parked bumper to bumper. In fact, the legendary Thoroughbred Man O' War, who raced in 1919 and 1920, had a stride length of 28 feet (8.5 meters) in full gallop [source: Bouyea].

With Thoroughbred horses capable of taking 150 strides a minute, the horses can reach speeds of more than 40 miles per hour (almost 65 kilometers per hour) [sources: Horse Hats, Jockey Club]. The horses' ability to endure such speeds during races that are commonly more than a mile long is due to the efficient oxygen delivery system the breed has developed, thanks in no small part to its large heart and efficient spleen. Horses can only breathe through their noses, and they breathe only in rhythm with their stride. They breathe in when extending and exhale when the legs come together, acting effectively as a bellows [source: APS].

The Thoroughbred's heart can circulate up to 75 gallons (284 liters) of blood each minute, and when running, the spleen introduces a perfusion of oxygen-rich red blood cells into the horse's bloodstream, increasing red blood cells from 35 to 65 percent of the total blood volume [source: APS]. The result is the horse's entire system is efficiently fed the oxygen it needs during races.

Keeping Track of Thoroughbreds

Arabians, like this bay-colored horse, and other members of the Oriental horse group, provided the foundation and quickness of the Thoroughbred breed.
Arabians, like this bay-colored horse, and other members of the Oriental horse group, provided the foundation and quickness of the Thoroughbred breed.

There were more than just the three foundation sires imported to the United Kingdom in the late-17th and early-18th centuries. As many as 200 other stallions from the Oriental group were brought in from the Middle East during that time and they too made large contributions to the Thoroughbred breed [source: Thoroughbred Heritage].

The bloodlines of these early contributors -- horses with names like Old Snap, Coneyskins and Lister Turk -- were lost in the way the Thoroughbred ancestry is traced. Bloodlines are traced through male horses only; a great running horse that produces only daughters may still have a major impact on the abilities of the Thoroughbred breed, but on paper its lineage is broken. Another way for a Thoroughbred's bloodline to become severed from the breed is if it mates with a horse from another breed. Any resulting foal will not be a Thoroughbred.


It takes a literally special horse to be a Thoroughbred. To be officially considered a Thoroughbred, a colt or a filly, must have been foaled (born) to full Thoroughbred parents, the dam (its mother) and the sire (its father). Keeping track of bloodlines may seem simple enough, but keep in mind that more than 100,000 Thoroughbreds are foaled worldwide annually, with more than 27,000 born in North America alone in 2010 [source: Allin, Schmitz].

To keep track of all of these live births as well as the original ancestral bloodlines, Thoroughbred horse racing organizations around the world maintain registries called stud books. In the late-18th century, James Weatherby, whose uncle was an early record keeper for the Jockey Club, took it upon himself to trace the bloodlines of all Thoroughbreds through their sires. He compiled the General Stud Book (GSB), first published in 1791 and maintained by the Weatherby family for the Jockey Club to this day.

The GSB provides the basis for all other stud books; other countries' stud books branch off from the original. Although the first Thoroughbred, a stallion named Bulle Rock, was imported to America in 1730, the American Stud Book's registry begins in 1868 [source: WGBH]. For a time, however, American Thoroughbreds couldn't make it into the General Stud Book. Records were lost during the Civil War, and to prevent the introduction of horses of dubious breeding, the Jockey Club passed the Jersey Act, a 1913 policy that allowed only horses whose parents had both been registered in previous editions to be included in the registry [source: Weatherbys Ltd.] This barred most American horses from the registry; the act was upheld until 1949. Following its repeal, the Jockey Club allowed horses registered in other official stud books into its own.

The Jockey Clubs: Rules of the Thoroughbred

Under stud book guidelines, a foal's color not matching either of its parents may lead to genetic blood testing to determine if it can be registered as a Thoroughbred.
Under stud book guidelines, a foal's color not matching either of its parents may lead to genetic blood testing to determine if it can be registered as a Thoroughbred.
Designpics/The Irish Image Collection/Thinkstock

The Thoroughbred registries around the world don't simply input live birth information for Thoroughbred foals. As we've seen, Thoroughbred stud books are closed registries, meaning they include only purebred Thoroughbreds born to purebred sires and dams. There are a great many rules and conditions a foal must meet to be accepted into a stud book. Since these rules establish the very definition of the Thoroughbred, this means the keepers of the stud books are also the de facto authorities over the breed itself.

The original Jockey Club has been in charge of regulating the breed in the United Kingdom (and, by extension, all over the world) since 1750. The American Jockey Club has controlled Thoroughbreds in North America since 1894. There has also been a trend toward globalizing the standards for the breed since 1976, when a committee of nations representing six regions of the world met to form the International Federation of Horseracing Authorities, which administers the International Stud Book [source: Jockey Club]. While national Jockey Clubs and other stub book authorities maintain strict control over their own books, they also now often defer to the rules established by the International Stud Book, which has 70 member nations.


Jockey Clubs create the rules for the breed, from what colorings constitute the Thoroughbred coats, to what type of insemination is allowable, to what an owner can name his horse. The American Jockey Club recognizes nine colorings, including:

  • Bay -- tan with black legs
  • Roan -- reddish brown
  • Chestnut -- a red-yellow or red brown
  • Palomino -- a golden-yellow horse with a blonde mane and tail

The American Jockey Club also accepts white, black, gray, gray/roan and brown [source: Jockey Club]. The International and General Stud Books recognize another coloring, painted, which features three subsets: skewbald, piebald and spotted [source: Weatherbys Ltd].

The Jockey Club also determines whether a horse's name is appropriate. There are some obvious regulations and some that aren't : A horse's name can't contain any kind of racial or social slur or offensive meaning, it can't be named after a famous person without that person's consent, it generally can't share the name with a winning or famous horse and it can't consist entirely of numbers, among other rules [source: Jockey Club].

Jockey Clubs and other stud book authorities are also responsible for tracking the international movement of horses, breeding data and, perhaps most importantly, also generally regulating Thoroughbred horse racing for its country or region.

Money in Thoroughbreds

For millennia, horses were raced in match races, where two horses were pitted only against one another. After Thoroughbreds were born, race fields (the number of horses in a race) grew.
For millennia, horses were raced in match races, where two horses were pitted only against one another. After Thoroughbreds were born, race fields (the number of horses in a race) grew.
Wathiq Khuzaie/Getty Images

Back in 1770, famed Stud Book compiler James Weatherby's uncle James was hired on as secretary to the Jockey Club of England and Ireland. Thoroughbred racing had begun with match races, where two horses belonging to wealthy aristocrats were pitted against one another. Eventually, entire days were filled with these races and soon races consisted of several horses racing each other. At about the same time, the purses for these races also grew in size, reaching as much as 2000 pounds sterling, an incredible sum in those days[source: TBHeritage]. The stakes for Thoroughbred horse racing grew enormously, and James Weatherby the elder was hired to keep track of it all.

Since then, Thoroughbred racing has managed to maintain its value. In the United States alone in 2010 the gross purses for all races held that year had a combined value of more than $1 billion [source: Jockey Club]. With so much money available for winning horses, the Thoroughbred breed has become a very valuable one. A study of the Keeneland, Ky., Yearling Sale in 2006 found that the average price of a Thoroughbred yearling that year was more than $126,000 [source: Thoroughbred Review]. By contrast, at a 2007 sale of Standardbred yearlings, horses bred for the decidedly less lucrative harness racing, the average price was $40,824 [source: SBAP].


As we've seen, the Thoroughbred is born to race, and between 60 and 65 percent of all yearlings foaled in a given year will be trained to race; only about 5 percent of these will win any substantial purse [source: Allin]. This is in part because the purses of the average race are closer to an average American middle class salary than a lottery windfall. For example, the average value of the combined purses for all the races held on a given day at Churchill Downs racetrack in Louisville, Ky., in 2008 was $411,000 [source: American Racing Manual]. Not too shabby, but divided among the 10 to 13 races the track holds daily, the purses decrease in value dramatically, especially considering horses don't run in more than one race a day.

Yet on the first Saturday in May, horses entered in a single race that year at Churchill Downs stand to earn $1.2 million for its owners. That race is the Kentucky Derby, which, along with the Preakness Stakes and the Belmont Stakes, is one-third of American Thoroughbred racing's Triple Crown. In the United Kingdom, the English Triple Crown consists the 2000 Guineas Stakes, the Epsom Derby and the St. Leger Stakes. While in both of these Triple Crowns, some races are called derbies, all of them are actually stakes races -- specifically Grade I stakes races, the most prestigious and generally most lucrative horse races. Only an estimated 0.2 percent of the 65 percent of those race-trained yearlings will win a Grade I stakes race [source: Allin].

Life after the Race: Death and Breeding

Thoroughbred horse Cigar raced as a 5-year-old and won more prize money than any other horse in history. He is shown here after winning the 1995 Breeders Cup at La Jolla, Calif.
Thoroughbred horse Cigar raced as a 5-year-old and won more prize money than any other horse in history. He is shown here after winning the 1995 Breeders Cup at La Jolla, Calif.

It costs a tremendous amount of money to not only buy, but also maintain a race horse. There are stable fees, the salaries of grooms, trainers and farm managers, transportation costs, food. Keeping race horses can be an expensive business. Horses also have a comparatively short racing life. Most graded races are open only to colts and fillies ages 2 to 3 (Triple Crown races are open only to 3-year-olds), and the average Thoroughbred horse that makes it to post has only 18 starts in his or her lifetime [source: Equinews]. Some of the greatest Thoroughbred racehorses, including Seabiscuit and Man O' War, raced for only two years before retiring. Others, like 16-consecutive race winner Cigar, continued racing as a 5-year-old, but for the most part a horse's racing life will last perhaps three or four years.

This means that an owner has a very limited opportunity to produce a return on investment through racing his Thoroughbred. An owner of a winning horse can continue to make income, however, by collecting stud fees when leasing a stallion out to sire. Owners of Thoroughbred fillies and mares pay fees reaching half a million dollars to owners of winning and well-known stallions to bring their horses to mate, called covering. One breeding syndicate -- investors who make money through stud fees -- paid $60 million for 3-year-old Fusachi after he won the Kentucky Derby to retire him to stud [source: WGBH]. Winning fillies may go on to collect fees or produce valuable foals as broodmares -- the female equivalent of a stud.


Strong objections have been raised against breeding syndicates -- and horse racing in general -- in recent years. Stallions may be forced to inseminate as many as three females a day at six-month stretches for 20 years or more by syndicates that increase profits through the sheer volume of fees collected [source: Animal Aid]. Other Thoroughbreds, including newborn foals of questionable financial worth, are simply discarded. In February 2011, the British paper The Observer reported that in Great Britain alone, 7,933 horses were slaughtered for meat there in 2010; that was a 50 percent increase over the prior year and an estimated 25 percent of that increase in slaughtered horses was thought to be Thoroughbreds [source: Doward].

In the United States, where horse slaughter was outlawed in 2007, an estimated 120,000 horses (Thoroughbreds and others) were exported to Canada for slaughter in 2009. In total, an estimated two-thirds of all Thoroughbred race horses are euthanized, slaughtered or abandoned once they're retired from racing [source: Mullane]. As a result, a number of Thoroughbred horse rescue organizations have emerged to take in and care for abandoned or threatened Thoroughbreds.

Selective Breeding in Thoroughbred Horses: A "Moral Crisis"

Eight Belles as she is led to the starting gate at the 2008 Kentucky Derby to start the race where she would finish second and suffer two fatal injuries that led to her euthanasia on the track.
Eight Belles as she is led to the starting gate at the 2008 Kentucky Derby to start the race where she would finish second and suffer two fatal injuries that led to her euthanasia on the track.
Jamie Squire/Getty Images

An apparent surplus of Thoroughbred horses has had visible effects on the breed. Financial pressures have led to a decrease in stallion coverings, which has led to a decline in the number of Thoroughbreds born each year, the foal crop. There was a more than 14-percent decline in foal crops between 2009 and 2010 [source: Shanklin]. The downturn in the global economy that began in 2008 had a pronounced effect on the number of Thoroughbreds on planet Earth.

In effect, the beginning of the 21st century saw the bursting of what amounts to a horse bubble. From a business perspective, an influx in investment in the 2000s led to an inflation in sale prices and stud fees. Increased potential profits led to an overproduction. Once prices normalized and dropped there was a "surplus" of Thoroughbreds, which, in turn, led to the increase in their killing. The predictable cascade of events followed the route of any market bubble, but this bubble had a pronounced effect on a breed of living animals.


The bursting of the bubble was welcomed by some. Horse prices had risen artificially high and as a result of overproduction, the quality of the horses produced declined. A decline in rampant mating means more dedication to the idea of quality over quantity among the breed.

Yet even the most purposefully applied selective breeding has produced terrible problems for the Thoroughbred breed. Because the perfect race horse is both fast and light, breeding has focused on Thoroughbreds with huge muscle concentrations but light bones. While Thoroughbreds have become faster over the years, they have also grown more fragile, producing a breed of horse with what one writer called "the heart of a locomotive [and] champagne-glass ankles" [source: Jenkins].

This has been horrifically apparent in some major races since the beginning of the 21st century. In 2006, the Kentucky Derby winner, a bay colt named Barbaro, broke three bones in his hind legs during the internationally televised Preakness Stakes held two weeks after the Derby. Following eight months of surgery, Barbaro was euthanized in 2007 [source: Associated Press]. The next year, Eight Belles, a gray filly, broke both her ankles just after finishing second in the 2008 Kentucky Derby. Her injuries were quickly deemed fatal and she was euthanized where she fell on the track at Churchill Downs [source: Associated Press].

While these two horses put a spotlight on the problems facing the Thoroughbred breed, they are two instances of a larger problem. The organization Animal Aid has documented 729 horses that were injured during races and euthanized or died in Great Britain alone from March 2007 to August 2011 [source: Horse Death Watch].

That the Thoroughbred breed wouldn't exist without human intervention and that very same intervention has led to tragedy among the breed has placed Thoroughbred racing, and by extension breeding, in a "moral crisis" [source: Jenkins]. Whether humans learn the lessons required to maintain the breed afforded by the bursting of the Thoroughbred bubble remains to be seen.

Lots More Information

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