horse, hoofed, herbivorous mammal now represented by a single extant genus, Equus. The term horse commonly refers only to the domestic Equus caballus and to the wild Przewalski's horse. (Other so-called wild horses are feral domestic horses or their descendants.) Adapted to plains environments, all Equus species, including the ass and the zebra, have lengthened foot bones ending in a single toe covered by a hoof, for fast running; teeth shaped for grinding grass; and intestinal protozoa for digesting cellulose. All species have tufts of hair on the tail, used against insects, and manes on the neck. Horses, zebras, and asses can interbreed, but the offspring are usually sterile. The offspring of a horse and a donkey (domestic ass) is called a mule.

A male horse is called a stallion, or if castrated, a gelding; a female is a mare; her offspring are foals—males are colts, females are fillies. A male parent is a sire, a female parent is a dam. A single foal is born after a gestation of about 11 months. Horses reach sexual maturity in about two years, but are not fully grown for about five years. The average life span is 18 years, but 30-year-old horses are common. The standard unit of height is a hand, equal to 4 in. (10 cm).

See horse racing; equestrianism.

History and Breeds

The earliest known direct ancestor of Equus, the eohippus [Gr.,=dawn horse], 10 to 20 in. (25-50 cm) tall, lived approximately 50 million years ago in both the Old and New Worlds. Equus originally evolved in North America by the late Pliocene epoch, about three million years ago, spreading to all continents except Australia. Horses disappeared from the Americas for unknown reasons about 10,000 years ago, to be reintroduced by Europeans, c.A.D. 1500.

Many species of Equus arose in the Old World. Horses were probably first domesticated by central Asian nomads around 3500 B.C. Horses were recorded in Mesopotamia and China (c.2000 B.C.), Greece (c.1700 B.C.), Egypt (c.1600 B.C.), and India (c.1500 B.C.). Horses were domesticated in W Europe no later than 1000 B.C. It is not known whether these early domesticated horses developed from a single wild race or from many local races.

Largely superseding the slower, less manageable ass, which had been domesticated much earlier, the horse's first known use was for drawing Mesopotamian war chariots. It was long reserved primarily for warfare and for transportation for the rich and well-born, while cheaper animals (e.g., oxen, mules, and donkeys) were used for lowlier work. Horses figured importantly in war and conquest in Europe, central Asia, and the Middle East for over 3,000 years. Early warriors rode bareback or with saddle cloths. The saddle and the stirrup were probably developed in China in the early Christian era, spread by Asian horsemen (such as the Huns), and adopted by Arabs and Europeans in the early Middle Ages. Arab cavalry conquered the Middle East and N Africa in the 7th cent. A.D. In the same period, armored knights were riding to battles in Europe. With highly developed cavalry tactics, the Mongols extended their 13th cent. empire from China to E Europe.

The Spanish conquistadors brought horses to the New World, where Native Americans soon acquired them from ranches and missions. The Plains Indians of North America quickly developed a horse culture that led to their ascendancy in numbers and power. Horses were used for hunting buffalo and other game, for warfare, and for pulling loads on a travois. Escaped Indian horses were ancestral to the mustang, the so-called wild horse of the W United States.

The two major groups of modern horses—the light, swift southern breeds, called light horses, and the heavy, powerful northern breeds, called draft horses—are believed to have arisen independently. The small breeds called ponies may derive from a southern, light horse or from a wild race.

Draft Horses

During Roman times the Gauls and other Europeans used horses of the heavy, northern type for pulling loads and other work. In the Middle Ages huge draft animals, over 16 hands (64 in./160 cm) high, were bred to carry armored knights as well as their own armor. As cavalry warfare declined, such medieval inventions as the horseshoe and the rigid horse-collar (see harness) made draft horses more useful for work. By the 19th cent. the draft horse had replaced the ox in N Europe and North America. Draft breeds common in the United States were the Belgian, the Clydesdale, the Percheron; and the Shire, also the most common draft horse in England.

Light Horses

Modern light horses, all descended in part from the Arabian horse, the oldest surviving breed of known lineage, include the Thoroughbred, celebrated as a racehorse; the American saddlebred horse, known for its easy gaits; the Morgan and the quarter horse, favored for riding and cow herding; and the Standardbred, or trotter, developed for light harness racing. The Appaloosa and the Pinto, much used in cow herding, are distinguished by their patterned colors. The palomino is not a breed but a color type. Among the small horses are the Shetland pony and Welsh pony. The terms cow pony and polo pony refer to the animal's use rather than its size or breed. Although little used for work today, horses are widely owned for recreational riding and show activities.




See A. Hyland, Equus (1990); E. H. Edwards and C. Geddes, ed., The Complete Horse Book (1991); K. R. Ward, The American Horse (1991); J. Clutton-Brock, Horse Power (1992); J. Holderness-Roddam, The New Complete Book of the Horse (1992); A. N. Greene, Horses at Work: Harnessing Power in Industrial America (2008).

Sea horse (Hippocampus erectus).

Any of about 24 species (family Syngnathidae) of fishes that usually live along warm seashores, clinging to plants with their forward-curled, prehensile tail. Species range from 1.5 to 12 in. (4–30 cm) long. Sea horses have bony rings instead of scales, and their eyes can move independently. They swim upright, propelling themselves horizontally with their fins and vertically with their swim bladder. They catch small organisms by sucking them quickly into their small mouths. The female deposits her eggs into a brood pouch beneath the male's tail, and the male expels the newly hatched young.

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Racing of quarter horses. It originated among British settlers in Virginia shortly after Jamestown was established in 1607. The course was traditionally a quarter-mile (400 m); today there are 11 officially sanctioned races, ranging from 220 to 870 yd (201 to 796 m). Timing is to the nearest .01 second.

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Breed of light horse developed in the U.S. from Thoroughbred, Morgan, American saddlebred, and other stock as a quarter-mile racer. Though overshadowed by the Thoroughbred, it found a place in the western and southwestern U.S. as a stock horse (see cutting horse). Modern quarter horses are short and stocky, with a muscular build and a deep, broad chest. They are noted for fast starting, turning, and stopping ability, short-distance speed, and intelligence. They stand 14.3–16 hands (57–64 in., 145–163 cm) high, weigh 950–1,200 lbs (431–544 kg), and have a calm, cooperative temperament.

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Art of training, riding, and handling horses. Good horsemanship requires that a rider control the animal's direction, gait, and speed with maximum effectiveness and minimum effort. Natural aids are a rider's balance, hands, voice, and legs; artificial aids include bits, reins, saddles, and spurs. Horsemanship was important to cavalrymen and cowboys, and is the fundamental element of dressage.

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Family Hippocastanaceae, composed of the buckeyes and the horse chestnuts (genus Aesculus), native to the northern temperate zone. The best-known species of horse chestnut is the common, or European, horse chestnut (A. hippocastanum), native to southeastern Europe but widely cultivated as a large shade and street tree. The Champs-Élysées in Paris is lined with rows of horse-chestnut trees.

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Rite of the Vedic religion in ancient India, performed by a king to celebrate his supremacy. A stallion was selected and allowed to roam freely for a year under the protection of a royal guard. It was said to symbolize the progress of the sun and the power of the king. If it was not captured during the year, it was brought back to the capital along with the rulers of lands it had entered. It was then sacrificed at a public ceremony, and the king assumed the h1 of universal monarch. The Buddha condemned the practice, but it was revived in the 2nd century BC and may have continued as late as the 11th century AD.

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Sport of running horses at speed. Typically, Thoroughbreds are raced with a rider astride and Standardbreds with the horse pulling a conveyance with a driver. Though racing has an ancient lineage, the first regularly organized national races were established in England under Charles II (r. 1660–85), and the first in North America were held on Long Island in 1665. These early races were match events between two or three horses and were run in heats; a horse had to complete at least two heats to be judged the winner. By the mid-18th century, larger fields of runners and single-race “dash” events were the norm. Handicap racing emerged in the mid-18th century as well, as gambling came to be a standard part of horse racing. Pari-mutuel betting was instituted in the 20th century. Thoroughbred racing, conducted on a flat, elliptical, mile-long track, attracts the largest purses, followed by harness racing and quarter-horse racing. The most important U.S. Thoroughbred races are the Kentucky Derby, Preakness Stakes, and Belmont Stakes. Seealso steeplechase.

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Any member of the dipteran genus Tabanus or, more generally, of the family Tabanidae. These stout flies range from as small as a housefly to as large as a bumblebee. Sometimes called greenheaded monsters, horseflies have metallic or iridescent eyes. Adults are fast, strong fliers usually found around streams, marshes, and wooded areas. They may carry animal diseases, including anthrax, tularemia, and trypanosomiasis. The bites of the bloodsucking females can be painful, and a swarm may suck more than 3 oz (about 90 ml) of blood a day from an animal. Males feed on nectar, honeydew, and plant sap. Horseflies of the genus Chrysops, usually called deerflies, are smaller and have dark markings on the wings.

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External features of a horse.

Equine species (Equus caballus) long used by humans as a means of transport and as a draft animal. Its earliest ancestor was the dawn horse (see Eohippus). The only living horse not descended from the domestic horse is Przewalski's horse. The horse was apparently first domesticated by nomadic peoples of Central Asia in the 3rd millennium BC. For many centuries horses were primarily used in warfare. The saddle was introduced in China in the first centuries AD. Horses were reintroduced to the New World, after wild horses had become extinct there some 10,000 years earlier, by the Spanish in the 16th century. A mature male is called a stallion or, if used for breeding, a stud; mature females are called mares. A castrated stallion is called a gelding. Young horses (foals) are also known as colts (males) and fillies (females). A horse's height is measured in 4-in. (10.2-cm) units, or hands, from the highest point of the back (withers) to the ground. Breeds are classified by size and build: draft (heavy) horses (e.g., Belgian, Percheron) are heavy-limbed and up to 20 hands high; ponies (e.g., Shetland, Iceland) are less than 14.2 hands high; and light horses (e.g., Arabian, Thoroughbred) are intermediate, rarely taller than 17 hands.

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Former name of a genus of ancestral horses, commonly called dawn horses, that flourished in North America during the Early Eocene Epoch (54.8–49 million years ago). It is now classified with European species in the genus Hyracotherium. Eohippus stood 1–2 ft (30–60 cm) high at the shoulders and was adapted to running, with hind legs longer than the forelegs. The body was lightly constructed, with slender legs and elongated feet that were functionally three-toed (though the front feet had four toes). The skull varied from shortened (primitive) to relatively long (more horselike).

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Light saddle horse trained to cut (isolate) livestock, especially cattle, from herds. Most are quarter horses, with the intelligence, speed, and ability to make quick starts, stops, and turns. A well-trained cutting horse can maneuver an animal away from a herd and into a corner with little direction from a rider or, in some cases, without a rider.

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Przewalski's horse (Equus caballus przewalskii).

Last wild equine subspecies (Equus caballus przewalskii) surviving into the 20th century. It is yellowish or light red (dun) and stands 12–14 hands (48–56 in., 122–142 cm) high. It has a dark mane and tail and usually a stripe on the back. The mane is short and erect with no forelock. It was discovered in western Mongolia in the 1870s. The horse disappeared in the wild in the 1960s, but the descendants of specimens that had earlier been taken to European zoos began to be reintroduced into the Mongolian steppe in the 1990s.

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(born 1842?, near present-day Rapid City, S.D., U.S.—died Sept. 5, 1877, Fort Robinson, Neb.) Oglala Sioux Indian chief. Refusing to abide by an 1868 treaty granting the Sioux a large reservation in the Black Hills, Crazy Horse led his warriors in continued raids against enemy tribes as well as against whites. In 1876 he joined with Cheyenne forces in a surprise attack against Gen. George Crook in southern Montana, forcing Crook's withdrawal. Crazy Horse then united with Chief Sitting Bull for the Battle of the Little Bighorn, where he helped annihilate Lt. Col. George Armstrong Custer's troops. In 1877, his tribe weakened by cold and hunger, Crazy Horse surrendered to Crook; removed to a military outpost in Nebraska, he was killed in a scuffle with soldiers.

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Earliest improved breed of horse, valued for its speed, stamina, beauty, intelligence, and gentleness. Its long history has been obscured by legend, but it was developed in Arabia by the 7th century AD. It has contributed its qualities to most modern breeds of light horses. It is compact and relatively small, with a small head, protruding eyes, wide nostrils, marked withers, and a short back. Its average height is about 15 hands (60 in. [152 cm]), its average weight 800–1,000 lbs (360–450 kg). Though many colours are possible, gray is the most common.

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The horse (Equus caballus) is a hoofed (ungulate) mammal, one of eight living species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today. Humans began to domesticate horses around 4500 BC, and their domestication is believed to have been widespread by 3000 BC; by 2000 BC the use of domesticated horses had spread throughout the Eurasian continent. Although most horses today are domesticated, there are still endangered populations of the Przewalski's Horse, the only remaining true wild horse, as well as more common feral horses which live in the wild but are descended from domesticated ancestors.

There is an extensive, specialized vocabulary used to describe equine-related concepts, covering everything from anatomy to life stages, size, colors, markings, breeds, locomotion, and behavior. Horses are anatomically designed to use speed to escape predators, and have a well-developed sense of balance and a strong fight-or-flight instinct. Related to this need to flee from predators in the wild is an unusual trait: horses are able to sleep both standing up and laying down. Female horses, called mares, carry their young for approximately 11 months, and a young horse, called a foal, can stand and run shortly following birth. Most horses begin training under saddle or in harness between the ages of two and four. They reach full adult development by age five, and have an average lifespan of between 25 and 30 years.

Horse breeds are loosely divided into three categories based on general temperament: spirited "hot bloods" with speed and endurance; "cold bloods," such as draft horses and some ponies, suitable for slow, heavy work; and "warmbloods," developed from crosses between hot bloods and cold bloods, often focusing on creating breeds for specific riding purposes, particularly in Europe. There are over 300 breeds of horses in the world today, developed for many different uses.

Horses and humans interact in many ways, not only in a wide variety of sport competitions and non-competitive recreational pursuits, but also in working activities including police work, agriculture, entertainment, assisted learning and therapy. Horses were historically used in warfare. A wide variety of riding and driving techniques have been developed, using many different styles of equipment and methods of control. Many products are derived from horses, including meat, milk, hide, hair, bone, and pharmaceuticals extracted from the urine of pregnant mares. Humans provide domesticated horses with food, water and shelter, as well as attention from specialists such as veterinarians and farriers.


Horse anatomy is described by a large number of specific terms, as illustrated by the chart to the right. Specific terms also describe various ages, colors and breeds.




The following terminology is used to describe horses of various ages:

  • Yearling: a horse of either sex that is between one and two years old.
  • Colt: a male horse under the age of four. A common terminology error is to call any young horse a "colt," when the term actually only refers to young male horses.
  • Filly: a female horse under the age of four.
  • Mare: a female horse four years old and older.
  • Stallion: a non-castrated male horse four years old and older. Some people, particularly in the UK, refer to a stallion as a "horse". A ridgling or "rig" is a stallion which has an undescended testicle. If both testicles are not descended, the horse may appear to be a gelding, but will still behave like a stallion.

In horse racing, the definitions of colt, filly, mare, and stallion may differ from those given above. In the UK, Thoroughbred horse racing defines a colt as a male less than five years old, and a filly as a female less than five years old. In the USA, both Thoroughbred racing and harness racing defines colts and fillies as four years old and younger.


The English-speaking world measures the height of horses in hands, abbreviated "h" or "hh," for "hands high," measured at the highest point of an animal's withers, where the neck meets the back, chosen as a stable point of the anatomy, unlike the head or neck, which move up and down; one hand is . Intermediate heights are defined by hands and inches, rounding to the lower measurement in hands, followed by a decimal point and the number of additional inches between 1 and 3. Thus a horse described as "15.2 h," is 15 hands, 2 inches in height. The size of horses varies by breed, but can also be influenced by nutrition.

The general rule for cutoff in height between what is considered a horse and a pony at maturity is 14.2 hands (). An animal 14.2 h or over is usually considered to be a horse and one less than 14.2 h as a pony. However, there are exceptions to the general rule. Some breeds which typically produce individuals both under and over 14.2 h are considered horses regardless of their height. Conversely, some pony breeds may have features in common with horses, and individual animals may occasionally mature at over 14.2 h, but are still considered to be ponies.

The distinction between a horse and pony is not simply a difference in height, but takes account of other aspects of phenotype or appearance, such as conformation and temperament. Ponies often exhibit thicker manes, tails and overall coat. They also have proportionally shorter legs, wider barrels, heavier bone, shorter and thicker necks, and short heads with broad foreheads. They often have calmer temperaments than horses and also a high level of equine intelligence that may or may not be used to cooperate with human handlers. In fact, small size, by itself, is sometimes not a factor at all. While the Shetland pony stands on average 10 hands high the Falabella and other miniature horses, which can be no taller than , the size of a medium-sized dog, are classified by their respective registries as very small horses rather than as ponies.

Light riding horses such as Arabians, Morgans, or Quarter Horses usually range in height from 14 to 16 hands and can weigh from . Larger riding horses such as Thoroughbreds, American Saddlebreds or Warmbloods usually start at about 15.2 hands and often are as tall as 17 hands weighing from . Heavy or draft horses such as the Clydesdale, Belgian, Percheron, and Shire are usually at least 16 to 18 hands high and can weigh from about .

The largest horse in recorded history was probably a Shire horse named Sampson, who lived during the late 1800s. He stood 21.2½ hands high and his peak weight was estimated at . The current record holder for the world's smallest horse is Thumbelina, a fully mature miniature horse affected by dwarfism. She is tall and weighs .

Colors and markings




Reproduction and development





Skeletal system

Horses have a skeleton that averages 205 bones. A significant difference between the horse skeleton, compared to that of a human, is the lack of a collarbone—the horse's front limb system is attached to the spinal column by a powerful set of muscles, tendons and ligaments that attach the shoulder blade to the torso. The horse's legs and hooves are also unique structures. Their leg bones are proportioned differently from those of a human. For example, the body part that is called a horse's "knee" is actually made up of the carpal bones that correspond to the human wrist. Similarly, the hock, contains the bones equivalent to those in the human ankle and heel. The lower leg bones of a horse correspond to the bones of the human hand or foot, and the fetlock (incorrectly called the "ankle") is actually the proximal sesamoid bones between the cannon bones (a single equivalent to the human metacarpal or metatarsal bones) and the proximal phalanges, located where one finds the "knuckles" of a human. A horse also has no muscles in its legs below the knees and hocks, only skin, hair, bone, tendons, ligaments, cartilage, and the assorted specialized tissues that make up the hoof.


The critical importance of the feet and legs is summed up by the traditional adage, "no foot, no horse". The horse hoof begins with the distal phalanges, the equivalent of the human fingertip or tip of the toe, surrounded by cartilage and other specialized, blood-rich soft tissues such as the laminae. The exterior hoof wall and horn of the sole is made of essentially the same material as a human fingernail. The end result is that a horse, weighing on average , travels on the same bones as a human on tiptoe. For the protection of the hoof under certain conditions, some horses have horseshoes placed on their feet by a professional farrier. The hoof continually grows, and needs to be trimmed (and horseshoes reset, if used) every five to eight weeks.


Horses are adapted to grazing. In an adult horse, there are 12 incisors, adapted to biting off the grass or other vegetation, at the front of the mouth. There are 24 teeth adapted for chewing, the premolars and molars, at the back of the mouth. Stallions and geldings have four additional teeth just behind the incisors, a type of canine teeth that are called "tushes." Some horses, both male and female, will also develop one to four very small vestigial teeth in front of the molars, known as "wolf" teeth, which are generally removed because they can interfere with the bit. There is an empty interdental space between the incisors and the molars where the bit rests directly on the bars (gums) of the horse's mouth when the horse is bridled.

The incisors show a distinct wear and growth pattern as the horse ages, as well as change in the angle at which the chewing surfaces meet. The teeth continue to erupt throughout life as they are worn down by grazing, so a very rough estimate of a horse's age can be made by an examination of its teeth, although diet and veterinary care can affect the rate of tooth wear.


Horses are herbivores with a digestive system adapted to a forage diet of grasses and other plant material, consumed steadily throughout the day. Therefore, compared to humans, they have a relatively small stomach but very long intestines to facilitate a steady flow of nutrients. A horse will eat of food per day and, under normal use, drink to of water. Horses are not ruminants, so they have only one stomach, like humans, but unlike humans, they can also digest cellulose from grasses due to the presence of a "hind gut" called the cecum, or "water gut," which food goes through before reaching the large intestine. Unlike humans, horses cannot vomit, so digestion problems can quickly cause colic, a leading cause of death.


The horse's senses are generally superior to those of a human. As prey animals, they must be aware of their surroundings at all times. They have the largest eyes of any land mammal, and because their eyes are positioned on the sides of their heads, horses have a range of vision of more than 350°, with approximately 65° of this being binocular (seen with both eyes) and the remaining 285° monocular (seen with only one eye). Horses have excellent day and night vision, but studies indicate that they have two-color, or dichromatic vision; their color vision is somewhat like red-green color blindness in humans. This means that certain colors, especially red and related colors, appear more green.

Their hearing is good, and the pinna of each ear can rotate up to 180°, giving the potential for 360° hearing without having to move the head. Their sense of smell, while much better than that of humans, is not their strongest asset; they rely to a greater extent on vision.

Horses have a great sense of balance, due partly to their ability to feel their footing and partly to highly developed proprioceptive abilities (the unconscious sense of where the body and limbs are at all times). A horse's sense of touch is well developed. The most sensitive areas are around the eyes, ears and nose. Via touch, horses perceive and respond immediately to changes in their environment, sensing contact as subtle as an insect landing anywhere on the body.

Horses have an advanced sense of taste that allows them to sort through grains and grasses to choose what they would most like to eat, and their prehensile lips can easily sort even the smallest grains. Horses generally will not eat poisonous plants. However, there are exceptions and horses will occasionally eat toxic amounts of poisonous plants even when there is adequate healthy food.


All horses move naturally with four basic gaits: the four-beat walk, which averages four miles per hour; the two-beat trot or jog, which averages per hour (faster for harness racing horses); and the leaping gaits known as the canter or lope (a three-beat gait that is per hour), and the gallop. The gallop averages per hour. The world record for a horse galloping over a short, sprint distance is per hour. Besides these basic gaits, some horses perform a two-beat pace, instead of the trot. In addition, there are several four-beat "ambling" gaits that are approximately the speed of a trot or pace, though smoother to ride. These include the lateral slow gait, rack, running walk, and tölt as well as the diagonal fox trot. Ambling gaits are often genetic traits in specific breeds, known collectively as gaited horses. In most cases, gaited horses replace the standard trot with one of the ambling gaits.


Horses are prey animals with a well-developed fight-or-flight instinct. Their first response to threat is to startle and usually flee, although they are known to stand their ground and defend themselves or their offspring in cases where flight is not possible, or when their young are threatened. They also tend to be curious; when startled, they will often hesitate an instant to ascertain the cause of their fright, and may not always flee from something that they perceive as non-threatening. Through selective breeding, some breeds of horses are quite docile, particularly certain large draft horses. Most light horse riding breeds were developed for speed, agility, alertness and endurance; natural qualities that extend from their wild ancestors. Horses are herd animals, with a clear hierarchy of rank, led by a dominant animal (usually a mare). They are also social creatures who are able to form companionship attachments to their own species and to other animals, including humans. They communicate in various ways, including vocalizations such as nickering or whinnying, mutual grooming, and body language. Many horses will become difficult to manage if they are isolated. Through proper training, it is possible to teach any horse to accept a human as a type of companion, and thus be comfortable away from other horses. When confined with insufficient companionship, exercise or stimulation, individuals may develop stable vices, an assortment of bad habits, mostly psychological in origin, that include wood chewing, wall kicking, "weaving" (rocking back and forth) and other problems.

Intelligence and learning

In the past, horses were considered unintelligent, with no abstract thinking ability, unable to generalize, and driven primarily by a herd mentality. However, recent studies show that they perform a number of cognitive tasks on a daily basis, and frequently engage in mental challenges that include food procurement and social system identification. They have also been shown to have good spatial discrimination abilities.

Studies have assessed equine intelligence in the realms of problem solving, learning speed, and knowledge retention. Results show that horses excel at simple learning, but also are able to solve advanced cognitive challenges that involve categorization and concept learning. They have been shown to learn from habituation, desensitization, Pavlovian conditioning, and operant conditioning. They respond to and learn from both positive and negative reinforcement.

Domesticated horses tend to face greater mental challenges than wild horses, due to living in artificial environments that stifle instinctual behavior while learning tasks that are not natural. Horses are creatures of habit that respond and adapt well to regimentation, and respond best when the same routines and techniques are used consistently. Some trainers believe that "intelligent" horses are reflections of intelligent trainers who effectively use response conditioning techniques and positive reinforcement to train in the style that fits best with an individual animal's natural inclinations. Others who handle horses regularly note that personality also may play a role separate from intelligence in determining how a given animal responds to various experiences.


Horses are mammals, and as such are all "warm-blooded" creatures, as opposed to reptiles, which are cold-blooded. However, these words have developed a separate meaning in the context of equine terminology, used to describe temperament, not body temperature. For example, the "hot-bloods," such as many race horses, exhibit more sensitivity and energy, while the "cold-bloods," such as most draft breeds, are quieter and calmer.

"Hot blooded" breeds include "oriental horses" such as the Akhal-Teke, Barb, Arabian horse and now-extinct Turkoman horse, as well as the Thoroughbred, a breed developed in England from the older oriental breeds. Hot bloods tend to be spirited, bold, and learn quickly. They are bred for agility and speed. They tend to be physically refined—thin-skinned, slim, and long-legged. The original oriental breeds were brought to Europe from the Middle East and North Africa when European breeders wished to infuse these traits into racing and light cavalry horses.

Muscular, heavy draft horses are known as "cold bloods," as they are bred not only for strength, but also to have the calm, patient temperament needed to pull a plow or a heavy carriage full of people. They are sometimes nicknamed "gentle giants. Well-known draft breeds include the Belgian and the Clydesdale. Some, like the Percheron are lighter and livelier, developed to pull carriages or to plow large fields in drier climates. Others, such as the Shire, are slower and more powerful, bred to plow fields with heavy, clay-based soils. The cold-blooded group also includes some pony breeds.

"Warmblood" breeds, such as the Trakehner or Hanoverian, developed when European carriage and war horses were crossed with Arabians or Thoroughbreds, producing a riding horse with more refinement than a draft horse, but greater size and more phlegmatic temperament than a lighter breed. Certain pony breeds with warmblood characteristics have been developed for smaller riders.

Today, the term "Warmblood" refers to a specific subset of sport horse breeds that have dominated the Olympic Games and international FEI competition in dressage and show jumping since the 1970s. Prior to that time, the term "warm blood" often referred to any cross between cold-blooded and hot-blooded breeds. Examples included breeds such as the Irish Draught or the Cleveland Bay. Less often, the term was even used to refer to breeds of light riding horse other than Thoroughbreds or Arabians, such as the Morgan horse.

Sleep patterns

Horses are able to sleep both standing up and lying down. In an adaptation from life in the wild, horses are able to enter light sleep by using a "stay apparatus" in their legs, allowing them to doze without collapsing. Horses sleep better when in groups because some animals will sleep while others stand guard to watch for predators. A horse kept alone will not sleep well because its instincts are to keep a constant eye out for danger.

Unlike humans, horses do not sleep in a solid, unbroken period of time, but take many short periods of rest. Horses may spend anywhere from four to fifteen hours a day in standing rest, and from a few minutes to several hours lying down. Total sleep time in a day may range from several minutes to a couple of hours, mostly in short intervals of about 15 minutes each.

Horses must lie down to reach REM sleep. They only have to lie down for an hour or two every few days to meet their minimum REM sleep requirements. However, if a horse is never allowed to lie down, after several days it will become sleep-deprived, and in rare cases may suddenly collapse as it involuntarily slips into REM sleep while still standing. This condition differs from narcolepsy, although horses may also suffer from that disorder.

Taxonomy and evolution

The horse as it is known today adapted by evolution to survive in areas of wide-open terrain with sparse vegetation, surviving in an ecosystem where other large grazing animals, especially ruminants, could not. Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during the Tertiary period. In the past, this order contained 14 families and many species, but only three families—Equidae (the horse and related species), the tapir and the rhinoceros—containing 18 known species have survived to the present day. The earliest known member of the Equidae family was the Hyracotherium, which lived between 45 and 55 million years ago, during the Eocene period and had 4 toes on each front foot, and 3 toes on each back foot. The extra toe on the front feet soon disappeared with the Mesohippus, which lived 32 to 37 million years ago, and by about 5 million years ago, the modern Equus had developed. The extra side toes shrank in size until they have vanished in modern horses. All that remains is a set of small vestigial bones on the leg above the hoof, known informally as ergots, chestnuts, or splint bones. Their legs also lengthened as their toes disappeared and until they were a hoofed animal capable of running at great speed.

Over millions of years, equid teeth also evolved from browsing on soft, tropical plants to adapt to browsing of drier plant material, and grazing of tougher plains grasses. Thus the proto-horses changed from leaf-eating forest-dwellers to grass-eating inhabitants of semi-arid regions worldwide, including the steppes of Eurasia and the Great Plains of North America. For reasons not fully understood, Equus caballus disappeared from North America around 10,000 years ago, at the end of the last ice age.

The "Four Foundations" theory

Modern DNA evidence suggests that domesticated horses evolved from multiple wild populations. Specifically, the "Four Foundations" theory suggests that the modern horse evolved from multiple ancient wild prototypes, each adapted to a given habitat. However, an older theory holds that there was only one type of wild horse, the Tarpan subtype, and all other types diverged in form after domestication to meet human needs.

Under the four foundations theory, all types and breeds of horses are thought to have developed from the following base prototypes:

Domestication and surviving wild species

Competing theories exist as to the time and place of initial domestication. The earliest evidence for the domestication of the horse comes from Ukraine and dates to approximately 4,000 BC. It is thought that the horse was completely domesticated by 3000 BC, and by 2000 BC there was a sharp increase in the number of horse bones found in human settlements in northwestern Europe, indicating the spread of domesticated horses throughout the continent.

Wild species surviving into modern times

A truly wild horse is a species or subspecies which has no ancestors that were ever domesticated. Therefore, most "wild" horses today are actually feral horses, animals that escaped or were turned loose from domestic herds and the descendants of those animals.

Only two types of truly wild horses survived into recorded history. One, the Tarpan (Equus ferus ferus) survived into the historical era, but became extinct in 1887. Its pure genetic line was lost, but three attempts have been made to re-create the Tarpan. In the early 1930s, Berlin Zoo Director Lutz Heck and Heinz Heck of the Munich Zoo began a program that by the 1960s produced the Heck horse. In 1936, Polish university professor Tadeusz Vetulani began a program using Konik horses, and in the mid-1960s Harry Hegard started a program in the United States using feral mustangs and local working ranch horses that has resulted in the Hegardt or Stroebel's Horse. None of the breeding programs were completely successful, although all three resulted in horses with many similarities to the Tarpan.

There is only one true wild horse species alive today, the Przewalski's Horse (Equus ferus przewalskii). It is rare Asian animal, also known as the Mongolian Wild Horse, Mongolian people know it as the taki, and the Kyrgyz people call it a kirtag. Small wild breeding populations of this animal, named after the Russian explorer Nikolai Przhevalsky, exist in Mongolia. There are also small populations maintained at zoos throughout the world. The species was considered extinct in the wild between 1969 and 1992, but a small breeding population was reestablished in the wild due to the conservations efforts by numerous zoos.

Feral populations

Feral horses are born and live in the wild, but are descended from domesticated animals. Many populations of feral horses exist throughout the world. Studies of feral herds have provided useful insights into the behavior of prehistoric horses, as well as greater understanding of the instincts and behaviors that drive horses that live in domesticated conditions.

Other modern equids

Besides the horse, there are seven other species of genus equus in the equidae family. These are the ass or donkey, Equus asinus; the Mountain Zebra, Equus zebra; Plains Zebra, Equus burchelli; Grévy's Zebra, Equus grevyi; the Kiang, Equus kiang; and the Kulan, Equus hemionus, including its subspecies, the Onager, Equus hemionus onager.

Horses can crossbreed with other members of the equus genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse, a cross between a zebra and a horse that is bred in Africa and used for trekking on Mount Kenya. With rare exceptions, most hybrids are sterile and cannot reproduce.


Horse breeds are groups of horses with distinctive characteristics that are transmitted consistently to their offspring, such as conformation, color, performance ability, or disposition. These inherited traits are usually the result of a combination of natural crosses and artificial selection methods aimed at producing horses for specific tasks. Certain breeds are known for certain talents. For example, Standardbreds are known for their speed in harness racing. Some breeds have been developed through centuries of crossings with other breeds, while others, such as Tennessee Walking Horses and Morgans, developed from a single sire from which all current breed members descend. There are more than 300 horse breeds in the world today.

Origin of breeds

Modern horse breeds developed in response to a need for "form to function", the necessity to develop certain physical characteristics in order to perform a certain type of work. Thus, powerful but refined breeds such as the Andalusian or the Lusitano developed in the Iberian peninsula as riding horses that also had a great aptitude for dressage, while heavy draft horses such as the Clydesdale and the Shire developed out of a need to perform demanding farm work and pull heavy wagons. Ponies of all breeds originally developed mainly from the need for a working animal that could fulfill specific local draft and transportation needs while surviving in harsh environments. However, by the 20th century, many pony breeds had Arabian and other blood added to make a more refined pony suitable for riding. Other horse breeds developed specifically for light agricultural work, heavy and light carriage and road work, various equestrian disciplines, or simply as pets.

Purebreds and registries

Horses have been selectively bred since their domestication. Today, there are over 300 breeds of horses in the world. However, the concept of purebred bloodstock and a controlled, written breed registry only became of significant importance in modern times. Today, the standards for defining and registration of different breeds vary. Sometimes purebred horses are called Thoroughbreds, which is incorrect; "Thoroughbred" is a specific breed of horse, while a "purebred" is a horse (or any other animal) with a defined pedigree recognized by a breed registry.

An early example of people who practiced selective horse breeding were the Bedouin, who had a reputation for careful breeding practices, keeping extensive pedigrees of their Arabian horses and placing great value upon pure bloodlines. Though these pedigrees were originally transmitted via an oral tradition, written pedigrees of Arabian horses can be found that date to the 14th century. In the same period of the early Renaissance, the Carthusian monks of southern Spain bred horses and kept meticulous pedigrees of the best bloodstock; the lineage survives to this day in the Andalusian horse. One of the earliest formal registries was General Stud Book for Thoroughbreds, which began in 1791 and traced back to the Arabian stallions imported to England from the Middle East that became the foundation stallions for the breed.

Some breed registries have a closed stud book, where registration is based on pedigree, and no outside animals can gain admittance. For example, a registered Thoroughbred or Arabian must have two registered parents of the same breed. Other breeds have a partially closed stud book but still allow certain infusions from other breeds. For example, the modern Appaloosa must have at least one Appaloosa parent, but may also have a Quarter Horse, Thoroughbred, or Arabian parent so long as the offspring exhibits appropriate color characteristics. The Quarter Horse normally requires both parents to be registered Quarter Horses, but allows "Appendix" registration of horses with one Thoroughbred parent, and the horse may earn its way to full registration by completing certain performance requirements.

Others, such as most of the warmblood breeds used in sport horse disciplines, have open stud books to varying degrees. While pedigree is considered, outside bloodlines are admitted to the registry if the horses meet the set standard for the registry. These registries usually require a studbook selection process involving judging of an individual animal's quality, performance, and conformation before registration is finalized. A few "registries," particularly some color breed registries, are very open and will allow membership of all horses that meet limited criteria, such as coat color and species, regardless of pedigree or conformation.

Breed registries also differ as to their acceptance or rejection of breeding technology. For example, all Jockey Club Thoroughbred registries require that a registered Thoroughbred be a product of a natural mating, so called "live cover". A foal born of two Thoroughbred parents, but by means of artificial insemination or embryo transfer, cannot be registered in the Thoroughbred studbook. On the other hand, since the advent of DNA testing to verify parentage, most breed registries now allow artificial insemination (AI), embryo transfer (ET), or both. The high value of stallions has helped with the acceptance of these techniques because they allow a stallion to breed more mares with each "collection," and greatly reduce the risk of injury during mating. Cloning of horses is highly controversial, and at the present time most mainstream breed registries will not accept cloned horses, though several cloned horses and mules have been produced.

Interaction with humans

Around the world, horses play a role within human cultures. Horses are used for leisure activities, sports, and working purposes. The Food and Agriculture Organization (FAO) reports that in 2003, China had the largest number of horses in the world with over 8 million, followed by Mexico (6,260,000), Brazil (5,900,500), the United States (5,300,000), and Argentina (3,655,000). The American Horse Council estimates that horse-related activities have a direct impact on the economy of the United States of over $39 billion, and when indirect spending is considered, the impact is over $102 billion. In a 2004 "poll" conducted by Animal Planet, more than 50,000 viewers from 73 countries voted for the horse as the world's 4th favorite animal.


Historically, equestrians honed their skills through competitions, games and races. Equestrian sports have the dual purpose of providing entertainment for crowds and creating and preserving the excellent horsemanship that was needed in battle. Many sports, such as dressage, eventing and show jumping, had origins in military training, which were focused on control and balance in both the horse and the rider. Other sports, such as rodeo, developed from practical skills such as those needed on working ranches. Sport hunting from horseback evolved from earlier practical hunting techniques. Horse racing, whether the horse was ridden or driven, evolved out of impromptu competitions between riders or drivers. The evolving competitions, requiring ever more demanding and specialized skills from both horse and rider, resulted in the systematic development of specialized breeds and equipment for each sport. The popularity of equestrian sports through the centuries has resulted in the preservation of skills that would otherwise have rapidly disappeared after horses stopped being used in combat.

Horses are trained to be ridden or driven in many different sporting events and competitions. Examples include show jumping, dressage, three-day eventing, competitive driving, endurance riding, gymkhana, rodeos and fox hunting. Horse shows, which have their origins in medieval European fairs, are held around the world as venues in which horses are competed, exhibited and sold. They host a huge range of classes, covering all of the mounted and harness disciplines, as well as "In-hand" classes where the horses are led, rather than ridden, to exhibit their conformation. The method of judging classes varies depending on the discipline, but winning awards usually depends on style and ability of both horse and rider. Sports such as polo do not judge the horse itself, but rather use the horse as a partner for human competitors as a necessary part of the game. Although the horse assists this process and requires specialized training to do so, the details of its performance are not judged, only the result of the rider's actions—be it getting a ball through a goal or some other achievement. Examples of these sports of partnership between human and animal also include jousting (reenacting the skills used by medieval knights), in which the main goal is for one rider to unseat the other, and buzkashi, a team game played throughout Central Asia, the aim being to capture a goat carcass while on horseback.

Horse racing is an equestrian sport and also a huge international industry, watched in almost every nation of the world. There are three types: "flat" racing; steeplechasing, i.e. racing over jumps; and harness racing, where horses trot or pace while pulling a driver in a small, light cart known as a sulky. A major part of horse racing's economic importance lies in the gambling associated with it.

Communication between human and horse is paramount in any equestrian activity; to aid this process horses are usually ridden with a saddle on their backs to assist the rider with balance and positioning, and a bridle or related headgear to assist the rider in maintaining control. Sometimes horses are ridden without a saddle, and occasionally, horses are trained to perform without a bridle or other headgear. Many horses are also driven, which requires a harness, bridle and some type of vehicle.


There are certain jobs that horses do very well, and no technology has yet developed that can fully replace them. For example, mounted police horses are still effective for certain types of patrol duties and crowd control. Cattle ranches still require riders on horseback to round up cattle that are scattered across remote, rugged terrain. Search and rescue organizations in some countries depend upon mounted teams to locate people, particularly hikers and children, and to provide disaster relief assistance. Horses can also be used in other areas where it is necessary to avoid vehicular disruption to delicate soil. Examples include areas such as nature reserves. They may also be the only form of transport allowed in wilderness areas. They are also quieter than motorized vehicles. Law enforcement officers such as park rangers or game wardens may use horses for patrols, and horses or mules may also be used for clearing trails or other work in areas of rough terrain where vehicles are less effective.

Some land management practices such as cultivating and logging can be efficiently performed with horses. In agriculture, less use of fossil fuels and increased environmental conservation can be seen over time with the use of draft animals such as horses. In forestry, logging can be done with horses and can result in reduced damage to soil structure and less damage to trees due to more selective logging. Although machinery has replaced horses in many parts of the world, an estimated 100 million horses, donkeys and mules are still used for agriculture and transportation in less developed areas such as Morocco, Kenya and Guatemala.

Entertainment and culture

Modern horses are often used to reenact many of their historical work purposes. Horses are used, complete with equipment that is authentic or a meticulously recreated replica, in various live action historical reenactments of specific periods of history, especially recreations of famous battles. Horses also are used to preserve cultural traditions and for ceremonial purposes. Countries such as the United Kingdom still use horse-drawn carriages to convey royalty and other VIPs to and from certain culturally significant events. Public exhibitions are another example, such as the Budweiser Clydesdales, seen in parades and other public settings, a team of draft horses that pull a beer wagon similar to that used before to the invention of the modern motorized truck.

Horses are frequently used in television and films to add authenticity to historical dramas as well as adding charm to films set in modern-day, or even futuristic science fiction settings. Both live horses and iconic images of horses are used in advertising to promote a variety of products. The horse frequently appears in coats of arms in heraldry. The horse can be represented as standing, trotting, courant (running) or salient (rearing). The horse may be saddled and bridled, harnessed, or without any harness whatsoever. The horse appears in the 12-year cycle of animals in the Chinese zodiac related to the Chinese calendar. According to Chinese folklore, each animal is associated with certain personality traits, and those born in the year of the horse are intelligent, independent and free-spirited.

Assisted learning and therapy

People of all ages with physical and mental disabilities obtain beneficial results from association with horses. Therapeutic riding is used to mentally and physically stimulate disabled persons and help them improve their lives through improved balance and coordination, increased self-confidence and a greater feeling of freedom and independence. The benefits of equestrian activity for people with disabilities has also been recognized with the addition of equestrian events to the Paralympic Games and recognition of para-equestrian events by the FEI. Hippotherapy and therapeutic horseback riding are names for different physical, occupational, and speech therapy treatment strategies that utilize equine movement. In hippotherapy, a therapist uses the horse's movement to provide improve their patient's cognitive, coordination, balance and fine motor skills, whereas therapeutic horseback riding uses specific riding skills.

Horses also provide psychological benefits to people whether they actually ride or not. "Equine-assisted" or "equine-facilitated" psychotherapy is a form of experiential psychotherapy that uses horses as companion animals to assist people with psychological problems, including anxiety disorders, psychotic disorders, mood disorders, behavioral difficulties, mental illness and those who are going through major life changes. Equine Assisted Learning (EAL) (also known as equine guided education or equine assisted professional development) is a field of experiential learning for corporate, professional and personal development. There are also experimental programs using horses in prison settings. Exposure to horses appears to improve the behavior of inmates in a prison setting and help reduce recidivism when they leave.


Horses in warfare have been seen for most of recorded history. The first archaeological evidence of horses used in warfare dates to between 3000 to 4000 BC, and the use of horses in warfare was widespread by the end of the Bronze Age. Although mechanization has largely replaced the horse as a weapon of war, horses are still seen today in limited military uses, mostly for ceremonial purposes, or for reconnaissance and transport activities in areas of rough terrain where motorized vehicles are ineffective. Horses have been used in the 21st century by the Janjaweed militias in the War in Darfur.


Horses have been used as raw material for many products made by humans throughout history, including byproducts from the slaughter of horses as well as materials collected from living horses.

Products collected from living horses include mare's milk, used by people with large horse herds, such as the Mongols, who let it ferment to produce kumis. Horse blood was once used as food by the Mongols and other nomadic tribes, who found it a convenient source of nutrition when traveling. Drinking their own horses' blood allowed the Mongols to ride for extended periods of time without stopping to eat. Today, the drug Premarin is a mixture of estrogens extracted from the urine of pregnant mares (pregnant mares' urine). It is a widely used drug for hormone replacement therapy. The tail hair of horses can be used for making bows for string instruments such as the violin, viola, cello, and double bass.

Horse meat has been used as food for humans and carnivorous animals throughout the ages. It is eaten in many parts of the world, though consumption is taboo in some cultures. Horsemeat has been an export industry in the United States and other countries, though legislation has periodically been introduced in the United States Congress which would end export from the United States. Horsehide leather has been used for boots, gloves, jackets, baseballs,and baseball gloves. Horse hooves can also be used to produce animal glue. Horse bones can be used to make implements. Specifically, in Italian cuisine, the horse tibia is sharpened into a probe called a spinto, which is used to test the readiness of a (pig) ham as it cures. In Asia, the saba is a horsehide vessel used in the production of kumis.


Horses are grazing animals, and their major source of nutrients is good-quality forage from hay or pasture. They can consume approximately 2% to 2.5% of their body weight in dry feed each day. Therefore, a adult horse could eat up to of food. Sometimes, concentrated feed such as grain is fed in addition to pasture or hay, especially when the animal is very active. When grain is fed, equine nutritionists recommend that 50% or more of the animal's diet by weight should still be forage.

Horses require a plentiful supply of clean water, a minimum of to per day. Although horses are adapted to live outside, they require shelter from the wind and precipitation, which can range from a simple shed or shelter to an elaborate stable.

Horses require routine hoof care from a farrier as well as regular vaccinations to protect against various diseases, and periodic dental examinations from a veterinarian or a specialized equine dentist. If horses are kept inside in a barn, they require regular daily exercise for their physical health and mental well-being. When turned outside, they require well-maintained, sturdy fences to be safely contained. Regular grooming is also helpful to help the horse maintain good health of the hair coat and underlying skin.

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