The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other horse breeds in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph (88.5 km/h). The American Quarter Horse is the most popular breed in the United States today, and the American Quarter Horse Association is the largest breed registry in the world, with more than 5 million American Quarter Horses registered.

The American Quarter Horse is well known both as a race horse and for its performance in rodeos, horse shows and as a working ranch horse. The compact body of the American Quarter Horse is well-suited to the intricate and speedy maneuvers required in reining, cutting, working cow horse, barrel racing, calf roping, and other western riding events, especially those involving live cattle. The American Quarter Horse is also shown in English disciplines, driving, and many other equestrian activities.

Breed history

Colonial era

In the 17th century, colonists on the eastern seaboard of what today is the United States began to cross imported English Thoroughbred horses with assorted "native" horses such as theChickasaw horse, which was a breed developed by Native American people from horses descended from Spain, developed from Iberian, Arabian and Barb stock brought to what is now the Southeastern United States by the Conquistadors.

One of the most famous of these early imports was Janus, a Thoroughbred who was the grandson of the Godolphin Arabian. He was foaled in 1746, and imported to colonial Virginia in 1756. The influence of Thoroughbreds like Janus contributed genes crucial to the development of the colonial "Quarter Horse." The breed is sometimes referred to as the "Famous American Quarter Running Horse." The resulting horse was small, hardy, and quick, and was used as a work horse during the week and a race horse on the weekends.

As flat racing became popular with the colonists, the Quarter Horse gained even more popularity as a sprinter over courses that, by necessity, were shorter than the classic racecourses of England, and were often no more than a straight stretch of road or flat piece of open land. When matched against a Thoroughbred, local sprinters often won. As the Thoroughbred breed became established in America, many colonial Quarter Horses were included in the original American stud books, starting a long association between the Thoroughbred breed and what would later become officially known as the "Quarter Horse," named after the distance at which it excelled, with some individuals being clocked at up to 55 mph.

Westward expansion

In the 19th century, pioneers heading West needed a hardy, willing horse. On the Great Plains, settlers encountered horses that descended from the Spanish stock Hernán Cortés and other Conquistadors had introduced into the viceroyalty of New Spain, which today includes the Southwestern United States and Mexico. These horses of the west included herds of feralanimals known as Mustangs, as well as horses domesticated by Native Americans, including the Comanche, Shoshoni and Nez Perce tribes. As the colonial Quarter Horse was crossed with these western horses, the pioneers found that the new crossbred had innate "cow sense," a natural instinct for working with cattle, making it popular with cattlemen onranches.

Development as a distinct breed

Early foundation sires of Quarter horse type included Steel Dust, foaled 1843; Shiloh (or Old Shiloh), foaled 1844; Old Cold Deck (1862); Lock's Rondo, one of many "Rondo" horses, foaled in 1880; Old Billy—again, one of many "Billy" horses—foaled circa 1880; Traveler, a stallion of unknown breeding, known to have been in Texas by 1889; and Peter McCue, foaled 1895, registered as a Thoroughbred but of disputed pedigree.

The main duty of the ranch horse in the American West was working cattle. Even after the invention of the automobile, horses were still irreplaceable for handling livestock on the range. Thus, major Texas cattle ranches, such as the King Ranch, the 6666 (Four Sixes) Ranch, and the Waggoner Ranch played a significant role in the development of the modern Quarter Horse. The skills needed by cowboys and their horses became the foundation of the rodeo, a contest which began with informal competition between cowboys and expanded to become a major competitive event throughout the west. To this day, the Quarter Horse dominates the sport both in speed events and in competition that emphasizes the handling of live cattle.

However, sprint races were also popular weekend entertainment and racing became a source of economic gain for breeders as well. As a result, more Thoroughbred blood was added back into the developing American Quarter Horse breed. The American Quarter Horse also benefitted from the addition of Arabian, Morgan and evenStandardbred bloodlines.

In 1940, the American Quarter Horse Association (AQHA) was formed by a group of horsemen and ranchers from the southwestern United States dedicated to preserving the pedigrees of their ranch horses. The horse honored with the first registration number, P-1, was Wimpy, a descendant of the King Ranch foundation sire Old Sorrel. Other sires alive at the founding of the AQHA were given the earliest registration numbers Joe Reed P-3, Chief P-5, Oklahoma Star P-6, Cowboy P-12, and Waggoner's Rainy Day P-13. The Thoroughbred race horseThree Bars, alive in the early years of the AQHA, is recognized by the American Quarter Horse Hall of Fame as one of the significant foundation sires for the Quarter Horse breed. Other significant Thoroughbred sires seen in early AQHA pedigrees include Rocket Bar, Top Deck and Depth Charge.

"Appendix" and "Foundation" horses

Since the American Quarter Horse formally established itself as a breed, the AQHA stud book has remained open to additional Thoroughbred blood via a performance standard. An "Appendix" American Quarter Horse is a first generation cross between a registered Thoroughbred and an American Quarter Horse or a cross between a "numbered" American Quarter Horse and an "appendix" American Quarter Horse. The resulting offspring is registered in the "appendix" of the American Quarter Horse Association's studbook, hence the nickname. Horses listed in the appendix may be entered in competition, but offspring are not initially eligible for full AQHA registration. If the Appendix horse meets certain conformational criteria and is shown or raced successfully in sanctioned AQHA events, the horse can earn its way from the appendix into the permanent studbook, making its offspring eligible for AQHA registration

Since Quarter Horse/Thoroughbred crosses continue to enter the official registry of the American Quarter Horse breed, this creates a continual gene flow from the Thoroughbred breed into the American Quarter Horse breed, which has altered many of the characteristics that typified the breed in the early years of its formation. Some breeders, who argue that the continued infusion of Thoroughbred bloodlines is beginning to compromise the integrity of the breed standard, favor the earlier style of horse, have created several separate organizations to promote and register "Foundation" Quarter Horses.

Quarter Horse Today

The American Quarter Horse is best known today as a show horse, race horse, reining and cutting horse, rodeo competitor, ranch horse, and all-around family horse. Quarter horses compete well in rodeo events such as barrel racing, calf roping and team roping; andgymkhana or O-Mok-See. Other stock horse events such as cutting and reining are open to all breeds but also dominated by American Quarter Horse. Large purses allow top competitors to earn over a million dollars in some of these events.

The breed is not only well-suited for western riding and cattle work. Many race tracks offer Quarter Horses a wide assortment of pari-mutuelhorse racing with purses in the millions. Quarter Horses have also been trained to compete in dressage and can be good jumpers. They are also used for recreational trail riding and in mounted police units.

The American Quarter Horse has also been exported worldwide. European nations such as Germany and Italy have imported large numbers of Quarter Horses. Next to the American Quarter Horse Association (which also encompasses Quarter Horses from Canada), the second largest registry of Quarter Horses is in Brazil, followed by Australia. With the internationalization of the discipline of reining and its acceptance as one of the official seven events of the World Equestrian Games, there is a growing international interest in Quarter Horses. Countries like Japan, Switzerland and Israel that did not have traditional stock horse industries have begun to compete with American Quarter Horses in their own nations and internationally. The American Quarter Horse is the most popular breed in the United States today, and the American Quarter Horse Association is the largest breed registry in the world, with over 5 million American Quarter Horses registered worldwide.

Breed characteristics

The modern Quarter Horse has a small, short, refined head with a straight profile, and a strong, well-muscled body, featuring a broad chest and powerful, rounded hindquarters. They usually stand between 14 and 16 hands high, although some Halter-type and English hunter-type horses may grow as tall as 17 hands.

There are two main body types: the stock type and the hunter or racing type. The stock horse type is shorter, more compact, stocky and well muscled, yet agile. The racing and hunter type Quarter Horses are somewhat taller and smoother muscled than the stock type, more closely resembling the Thoroughbred.

Stock type

Reining and cutting horses are smaller in stature, with quick, agile movements and very powerful hindquarters. Western pleasure show horses are often slightly taller, with slower movements, smoother gaits, and a somewhat more level topline – though still featuring the powerful hindquarters characteristic of the Quarter Horse.

Halter type

Horses shown in-hand in Halter competition are larger yet, with a very heavily muscled appearance, while retaining small heads with wide jowls and refined muzzles. There is controversy amongst owners, breeder and veterinarians regarding the health effects of the extreme muscle mass that is currently fashionable in the specialized halter horse, which typically is 15.2 to 16 hands and weighs in at over 1,200 pounds (540 kg) when fitted for halter competition. Not only are there concerns about the weight to frame ratio on the horse's skeletal system, but the massive build is also linked to HYPP. (See Genetic diseases below)

Racing and hunter type

Quarter Horse race horses are bred to sprint short distances ranging from 220 to 870 yards. Thus, they have long legs and are leaner than their stock type counterparts, but are still characterized by muscular hindquarters and powerful legs. Quarter horses race primarily against other Quarter horses, and their sprinting ability has earned them the nickname, "the world's fastest athlete." The show hunter type is slimmer, even more closely resembling a Thoroughbred, usually reflecting a higher percentage of appendix breeding. They are shown in hunter/jumper classes at both breed shows and in open USEF-rated horse show competition.

Colors

Quarter Horses come in nearly all colors. The most common color is sorrel, a brownish red, part of the color group called chestnut by most other breed registries. Other recognized colors include bay, black, brown, buckskin, palomino, gray, dun, red dun, grullo (also occasionally referred to as blue dun), red roan, blue roan, bay roan, perlino, cremello, and white. In the past, spotted color patterns were excluded, but now with the advent of DNA testing to verify parentage, the registry accepts all colors as long as both parents are registered.

Genetic diseases

There are several genetic diseases of concern to Quarter Horse breeders:

• Hyperkalemic periodic paralysis (HYPP), which is caused by an autosomal dominant gene linked to the stallion Impressive. It is characterized by uncontrollable muscle twitching and substantial muscle weakness or paralysis among affected horses. Because it is a dominant gene, only one parent has to have the gene for it to be transmitted to offspring. There is a DNA test for HYPP, which is required by the AQHA. Since 2007, the AQHA bars registration of horses who possess the homozygous form (H/H) of the gene,^[25] and thoughheterozygous (H/N) horses, are still eligible for registration, altering that status is currently being discussed. Additionally all Quarter Horses born 2007 or later that are confirmed to be descendants of Impressive must carry a note about the risks of HYPP on their registration papers. Due to HYPP, the halter classes are undergoing significant changes. Halter classes are dominated by the Impressive bloodline. Impressive, a very prolific halter horse, brought to the stock breeds the muscle mass that is popular in halter competition today. This muscle mass is linked to HYPP, and as the condition is reduced within the breed, the style of horse in halter classes is also likely to change. Already there have been rule changes, including the creation of a "Performance Halter class" in which a horse must possess a Register of Merit in performance or racing before it can compete.^[26]

• Malignant hyperthermia. A causative mutated allele, ryanodine receptor 1 gene (RyR1) at nucleotide C7360G, generating a R2454G amino acid substitution.^[27] has been identified in the American Quarter Horse and breeds with Quarter Horse ancestry, inherited as an autosomal dominant^[28][29] It can be caused by overwork, anesthesia, or stress.^[30]

• Hereditary Equine Regional Dermal Asthenia (HERDA), also known as hyperelastosis cutis (HC). This is caused by an autosomal recessive gene, and thus, unlike HYPP, HERDA can only be transmitted if both parents carry the gene. When a horse has this disease, there is a collagen defect that results in the layers of skin not being held firmly together. Thus, when the horse is ridden under saddle or suffers trauma to the skin, the outer layer often splits or separates from the deeper layer, or it can tear off completely. It rarely heals without disfiguring scars. Sunburn can also be a concern. In dramatic cases, the skin can split along the back and even roll down the sides, with the horse literally being skinned alive. Most horses with HERDA are euthanized for humane reasons between the age of two and four years. The very hotly debated and controversial theory, put forth by researchers at Cornell University and Mississippi State University is that the sire line of the great foundation stallion Poco Bueno is implicated as the origin of the disease. As of May 9, 2007, Researchers working independently at Cornell University and at the University of California, Davis announced that a DNA test for HERDA has been developed. Over 1,500 horses were tested during the development phase of the test, which is now available to the general public through both institutions.^[31]

• Glycogen Branching Enzyme Deficiency (GBED) is a genetic disease where the horse is lacking an enzyme necessary for storing glycogen, the horse's heart muscle and skeletal muscles cannot function, leading to rapid death. The disease occurs in foals who are homozygous for the lethal GBED allele, meaning both parents carry one copy of the gene. The stallion King P-234 has been linked to this disease. There is a DNA blood test for this gene.^[32]

• Equine polysaccharide storage myopathy, also called EPSM or PSSM, is a metabolic muscular condition in horses that causes tying up, and is also related to a glycogen storage disorder.^[33] While also seen in some draft horse breeds, PSSM has been traced to three specific but undisclosed bloodlines in Quarter Horses, with an autosomal recessive inheritance pattern.^[34] 48% of Quarter Horses with symptoms of neuromuscular disease have PSSM. To some extent it can be diet controlled with specialized low-starch diets, but genetic testing is advised before breeding, as the condition exists at a subclinical level in approximately 6% of the general Quarter Horse population.

• Lethal White Syndrome. Although "cropout" Quarter Horses with Paint markings were not allowed to be registered for many years, the gene for such markings is a recessive and continued to periodically appear in Quarter Horse foals. Thus, it is believed that some Quarter Horses may carry the gene for Lethal White Syndrome. There is a DNA test for this condition.