Horse

The horse is a hoofed, herbivorous mammal of the family Equidae, a single species whose numerous varieties are known as breeds; it served widely as a draft animal and as a chief means of transportation before the arrival of mechanized vehicles. Its scientific name is Equus caballus. Equus is the only surviving genus within a family that was once diverse.

The horse belongs to the family Equidae, the group that also contains the asses and the zebras, and is placed within the order Perissodactyla, the odd-toed ungulates. That ordinal name reflects a structural distinction in the foot: perissodactyls bear their weight on an odd number of toes, whereas the even-toed ungulates do not. The closest living relatives of the horse are not the cattle or the deer but the rhinoceroses and the tapirs, which share the same odd-toed ancestry. Standard reference works treat the living members of the genus Equus as comprising seven species, among them the domestic horse, Przewalski's horse, three species of asses and three species of zebras.

It is a critically endangered species found in Mongolia.

Domestication is placed at approximately 6,000 years ago, while the ancestors of modern horses were domesticated in the northern Caucasus region, in what is now southern Russia, and were bred for their stress tolerance and back strength. Selection in early domestic horses favoured back strength and stress tolerance alongside docility-linked genes such as GSDMC and ZFPM1.

Przewalski's horses became extinct in the wild after harsh winter conditions, inbreeding with local horses and excessive hunting, and the subspecies was last seen in the wild in the late 1960s, though captive breeding programs later reintroduced the horses to some of their former habitats. Zoos have been instrumental in preventing the Przewalski's horse from dying out, and the approximately 1,900 animals alive today are all descended from 14 founders caught in the wild between 1910 and 1960 and bred in captivity.

The horse is a large ungulate whose body mass spans 227 to 900 kg (500.00 to 1982.38 lb) and whose height at the withers falls between 0.9 and 1.7 meters. This wide range reflects differences in breed and intended use rather than a single fixed form. The animal stands on long, slender legs and carries a muscular, deep torso, with a long, thick neck completing the profile.

The foot is the most distinctive structural feature: the modern horse bears a single toe, terminating in an oval-shaped hoof. The lineage leading to this condition passed through stages in which most early horses had three full-sized toes touching the ground, while Hyracotherium had four front toes. Later horses stood on three toes, with the middle toe doing most of the work, before the modern single-toed foot emerged.

The horse relies on vision as its primary sense, and its long, upright ears serve acute hearing. Whiskers on the nostrils, muzzle and cheeks provide tactile sensitivity. As a grazing animal it feeds on true grasses, while domestic horses are given grains including oats, barley, corn, wheat, flax and soybeans. Digestion of fibrous plant material takes place through hindgut fermentation in the cecum, carried out by symbiotic bacteria — a system that contrasts with the foregut fermentation of ruminants.

Horses live in herds or bands organized by social hierarchy. A band may contain up to 26 mares and 5 stallions.

The horse's reproductive cycle is long by mammalian standards: gestation averages about 335 days, though it can range from 287 to 419 days. Foals are precocial, able to stand within an hour of birth and to walk within four to five hours. The typical lifespan of a horse is 25 to 30 years, with a maximum recorded longevity of 61 years.

The terminology of the species reflects its long association with human management. A mature male is a stallion, a mature female a mare, and a breeding stallion is called a stud. A castrated stallion is a gelding. The young are known as foals, with males called colts and females called fillies.

The oldest known horse is Hyracotherium, a small dog-sized animal with a primitive short face, eye sockets set in the middle of the skull, and a short diastema between the front teeth and the cheek teeth. Species of Equus, the genus that includes living horses, asses and zebras, have lived from 5 million years ago until the present, and fossils of the genus have been found on every continent except Australia and Antarctica. The modern horse, Equus caballus, evolved on the North American continent and disappeared from it around 10,000 years ago at the end of the Pleistocene epoch, surviving on the European and Asian continent and later being brought back to North America by the Spanish in the 1500s, when stray horses became known as mustangs.

The modern domestic horse descends from the DOM2 lineage, which arose in the lower Volga-Don region of the Western Eurasian steppes. By around 2200 to 2000 BC the typical DOM2 ancestry profile had appeared outside the Western Eurasian steppes in Bohemia, the lower Danube and central Anatolia, spreading across Eurasia shortly afterwards and eventually replacing all pre-existing lineages.

Przewalski's horses were not the ancestors of today's domestic horse, and horse domestication along with the drinking of horse milk likely began about 1500 kilometers to the west in the Pontic-Caspian steppe.

Modern domestic horses expanded rapidly across Eurasia from about 2000 BC and ultimately replaced almost all other local populations, in synchrony with equestrian material culture including Sintashta spoke-wheeled chariots.

More than 200 breeds of horse are recognized around the world, and however different they may appear, all of them belong to a single species, Equus caballus. These breeds were shaped over thousands of years by mating horses that carried desirable traits.

The Shetland pony of the Shetland Islands in Scotland is thought to have existed since the Bronze Age, and in the 19th century it was used as a pit pony in the mines of Great Britain. It is a very powerful and popular child's mount.

About 200 years ago, English horse breeders mated light, swift Arabians with local riding horses, and this created the Thoroughbred, a lean, leggy, super-speedy breed used in horse racing.

Przewalski's horse is the last truly wild horse, a stocky, short, pot-bellied animal with a spiky mane, dark brown legs, and a long dark dorsal stripe along the back. It stands 48 to 56 inches at the shoulder and weighs 440 to 750 pounds, with a tail about 90 centimeters long. It is listed as Endangered on the IUCN Red List, and only around 2000 of these stocky caramel-colored equines exist today.

The species inhabits Mongolia, Kazakstan, and China, where it has a thick warm coat, a long beard, and neck hair. Its home ranges span 1 to 12 square miles, and bachelor stallions may cover more than 13 miles a day.

Mitochondrial DNA suggests that Przewalski's horse diverged from a common ancestor 500,000 years ago. A 2018 study found that these horses may actually be descendants of domesticated equines that returned to the wild, which would make them feral rather than wild.

Horses known as the takhi grazed the grasslands of Asia and Europe thousands of years ago, and the animals became known as Przewalski's horses after Russian explorer Nikolai Przewalski described and examined their bones in the late 1800s.

Prague Zoo has run a breeding programme for Przewalski's horses since 1932, producing more than 250 foals over its first 90 years without interruption, including through the Second World War. In 1998 and 2000 the zoo joined the international reintroduction effort by providing four Przewalski's horses for transports to Takhiin Tal in the Dzungarian Gobi in Mongolia and to Khustain Nuruu in the Mongol Daguur Steppe.

The Colonial Spanish horse, a group of closely related breeds descending from horses brought to the Americas by Spanish explorers, conquistadors and colonists, is listed with a conservation status of critical on The Livestock Conservancy's Conservation Priority List. Adults weigh 700-900 lbs and have an even and gentle temperament, and some are gaited with an unusually long stride.

The reintroduction of horses changed the social and environmental landscape of the Great Plains, most notably for the Plains Indians, whose acquisition of the horse changed their culture from pedestrian hunter-gatherers to mounted buffalo hunters and warriors.

The Bureau of Land Management manages and protects wild horses and burros on 25.5 million acres of public lands across 10 Western states as part of its mission to administer those lands for a variety of uses.

The horse reshaped how humans moved, farmed, fought, competed, communicated and travelled. The chariot was the supreme military weapon in Eurasia roughly from 1700 BCE to 500 BCE, and it was also used for hunting and in sporting contests such as the Olympic Games and the Roman Circus Maximus. It was invented in the steppe, perhaps originally as an improved tool for hunting, roughly by 2000 BCE in the area just east of the southern Ural mountains, where the oldest chariots have been unearthed.

Horsemeat is still consumed in parts of Europe and Iceland and is included in many pet foods, while glue is made from horse bones and cartilage and tetanus antitoxin is obtained from the blood serum of horses previously inoculated with tetanus toxoid.

• around 55 million years ago to around 45 million years ago
  Hyracotherium (eohippus)
  Hyracotherium (eohippus) lived.
• 5 million years ago
  Equus species begin
  Equus species begin.
• around 3500 BC
  Botai site
  Botai site in Central Asia with bridling, milking and corralling evidence.
• around 2200 BC
  DOM2 horses spread
  DOM2 horses spread outside the Western Eurasian steppes.
• around 2000 BC
  Modern domestic horses expand
  Modern domestic horses expand rapidly across Eurasia.
• around 2000 to 1800 BC
  Spoke-wheeled chariots emerge
  Spoke-wheeled chariots emerge in the Trans-Ural Sintashta culture.
• 1294 BCE
  Battle of Kadesh
  Battle of Kadesh.
• roughly 1700 BCE to 500 BCE
  Chariot as supreme military weapon
  Chariot as supreme military weapon in Eurasia.
• 1500s
  Spanish bring horses back to North America
  Spanish bring horses back to North America.
• 1910 to 1960
  Przewalski's horse founders caught
  14 Przewalski's horse founders caught in the wild.
• 1932
  Prague Zoo breeding programme begins
  Prague Zoo breeding programme begins.
• 1971
  Wild Free-Roaming Horses and Burros Act passed
  Wild Free-Roaming Horses and Burros Act passed.