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Domestic Horse
Conservation status
Domesticated
Scientific classification
Kingdom: Animalia   Phylum: Chordata   Class: Mammalia   Order: Perissodactyla   Family: Equidae   Genus: Equus   Species: E. caballus
Binomial name
Equus caballus Linnaeus, 1758
Synonyms
Equus ferus caballus (see text) Equus laurentius

The horse (Equus caballus) is a odd-toed 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, with domestication of the horse believed to have been widespread by 3000 BC. By 2000 BC the use of domesticated horses had spread throughout the Eurasian continent. While most horses today are domesticated and live in close proximity to humans, there are still endangered populations of the Przewalski's horse, the only remaining true wild horse that has no domesticated ancestors, as well as more common feral horses, such as the American Mustang, which live in the wild but are descended from domesticated ancestors.

Horses are described with a large number of specific terms that describe everything from their anatomy to their life stages, colors, white markings, breeds, locomotion and behavior. They have a wide range of sizes, and are anatomically designed as a herbivore with the ability to use speed to escape predators. Horses 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 a unique 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, reaching 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 creating specially-developed breeds, particularly in Europe. There are over 300 breeds of horses in the world today, developed for many different uses. Some regions in the world are known for a specialty in development of a particular breed or set of breeds, such as harness horses in Russia or draft and pony breeds in Great Britain.

Horses and humans have extensive interactions today, not only in a wide variety of sports competitions and non-competitive recreational pursuits, but also working activities such as police, draft work, entertainment, assisted learning and therapy, and modern warfare. Many products are also made from horse meat, milk, hide, hair and bone, as well as pharmaceuticals made from the urine of pregnant mares.

Domesticated horses require specialized care to stay healthy, including proper provision of food, water and shelter, but also additional care from specialists such as veterinarians and horseshoers, or farriers. There is a wide variety of riding and driving techniques for managing horses, using many different styles of equipment and methods of control.

Biology

Main article: Equine anatomy

Parts of a horse (click to enlarge).

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

Age

Depending on breed, management and environment, the domestic horse today has a life expectancy of 25 to 30 years. It is uncommon, but a few horses live into their 40s, and, occasionally, beyond. The oldest verifiable record was "Old Billy," a horse that lived in the 19th century to the age of 62.^[1] In modern times, Sugar Puff, who had been listed in the Guinness Book of World Records as the world's oldest then-living pony, died at age 56.^[2]

Regardless of a horse's actual birthdate, for most competition purposes, horses are considered a year older on January 1 of each year in the northern hemisphere^[3][4] and August 1 in the southern hemisphere.^[5] The exception is endurance riding, where the minimum age to compete is based on the horse's actual calendar age.^[6] A very rough estimate of a horse's age can be made from looking at its teeth.^[4]

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

• Foal: a horse of either sex less than one year old. A nursing foal is sometimes called a suckling and a foal that has been weaned is called a weanling.^[7] Most domesticated foals are weaned at 5 to 7 months of age, although foals can be weaned at 4 months with no adverse effects.^[8]
• Yearling: a horse of either sex that is between one and two years old.^[9]
• Colt: a male horse under the age of four.^[10] 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.^[7]
• Mare: a female horse four years old and older.^[11]
• Stallion: a non-castrated male horse four years old and older.^[12] Some people, particularly in the UK, refer to a stallion as a "horse."^[13] 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.^[14]
• Gelding: a castrated male horse of any age,^[7] though for convenience sake, many people also refer to a young gelding under the age of four as a "colt."

In horse racing, the definitions of colt, filly, mare, and stallion or horse may differ from those given above. In the United Kingdom, Thoroughbred horse racing defines a colt as a male horse less than five years old, and a filly as a female horse less than five years old.^[15] In the USA, both Thoroughbred racing and harness racing defines colts and fillies as four years old and younger.^[16]

Size

The English-speaking world measures the height of horses in hands, abbreviated "h" or "hh," for "hands high," and is measured at the highest point of an animal's withers, where the neck meets the back. One hand is 4 inches (10 cm). 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 hh," is 15 hands, 2 inches, or 62 inches (160 cm) in height.^[17]

Size varies greatly among horse breeds, as with this full-sized horse and a miniature horse.

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 (58 inches (150 cm)) as measured at the withers. An animal 14.2h or over is usually considered a horse and one less than 14.2h is a pony.^[18] However, there are exceptions to the general rule. Some smaller horse breeds who typically produce individual horses both under and over 14.2h are considered "horses" regardless of height.^[19] Likewise, some pony breeds, such as the Welsh pony, share some features of horses and individual animals may occasionally mature at over 14.2h, but are still considered ponies.^[20]

The difference between a horse and pony is not simply a height difference, but also a difference in phenotype or appearance. There are noticeable differences in 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.^[18]

Light riding horses such as Arabians, Morgans, or Quarter Horses usually range in height from 14.0 to 16.0 hands (56 to 64 inches (140 to 160 cm)) and can weigh from 850 to 1,200 pounds (390 to 540 kg). Larger riding horses such as Thoroughbreds, American Saddlebreds or Warmbloods usually start at about 15.2 hands (62 inches (160 cm)) and often are as tall as 17 hands (68 inches (170 cm)), weighing from 1,100 to 1,500 pounds (500 to 680 kg). Heavy or draft horses such as the Clydesdale, Belgian, Percheron, and Shire are usually at least 16.0 to 18.0 hands (64 to 72 inches (160 to 180 cm)) high and can weigh from about 1,500 to 2,000 pounds (680 to 910 kg). While ponies technically are not to be taller than 14.2h (147 cm), they may be much smaller, down to the Shetland pony at around 10 hands (40 inches (100 cm)),^[21] and the Falabella which can be no taller than 30 inches (76 cm), the size of a medium-sized dog. However, while many miniature horse breeds are small as or smaller than a Shetland pony, because they are bred to have a horse phenotype (appearance), many breeders and registries classify them as very small horses rather than ponies.^[22]

The largest horse in recorded history was probably a Shire horse named Sampson, who lived during the late 1800s. He stood 21.2œ hands high (86.5 inches (220 cm)), and his peak weight was estimated at 3,360 pounds (1,520 kg).^[23] The current record holder for the world's smallest horse is Thumbelina, a fully mature miniature horse affected by dwarfism. She is 17 inches (43 cm) tall and weighs 60 pounds (27 kg).^[24]

Colors and markings

Main articles: Equine coat color, Equine coat color genetics, and Horse markings

Bay (left) and chestnut (sometimes called "sorrel") are two of the most common horse coat colors, seen in almost all breeds.

Horses exhibit a diverse array of coat colors, most have distinctive markings, and a specialized vocabulary has evolved to describe them. Often, one will refer to a horse in the field by its coat color first rather than by breed or by sex.^[25] In spite of the adage that "a good horse is never a bad color,"^[26] flashy or unusual colors are sometimes very popular, as are horses with particularly attractive markings. Horses of the same color may be distinguished from one another by their markings.^[27]

The genetics of many horse coat colors has been mapped, although research continues to be conducted on the identification of specific genes and mutations that result in specific color traits.^[28] Essentially, all horse colors begin with a genetic base of "red" (chestnut) or "black," with the addition of alleles for suppression of color, dilution of color, spotting, graying, or other effects acting upon the base colors in various combinations and varying degrees of dominance or recessivity that create the dozens of possible shades of horses.^[29]

Horses that are light in color are often misnamed as being "white" horses. A horse that looks pure white is, in most cases, actually a middle-aged or older gray. Grays have black skin underneath their white hair coat (with the exception of small amounts of pink skin under white markings). This is how a gray horse can be distinguished from a white horse. The only horses properly called white are those with pink skin under a white hair coat, a fairly rare occurrence.^[30] There are no truly albino horses, with pink skin and red eyes. True albinism is a lethal gene in horses.^[31]

Reproduction and development

Main article: Horse breeding

Pregnancy lasts for approximately 335-340 days^[32] and usually results in one foal. Twins are rare. Colts are carried on average about 4 days longer than fillies.^[33] Horses are a precocial species, and foals are born capable of standing and running within a short time following birth.^[34]

Mares and foals.

Horses, particularly colts, may sometimes be physically capable of reproduction at approximately 18 months but in practice are rarely allowed to breed until a minimum age of 3 years, especially females.^[32] Horses four years old are considered mature, though the skeleton usually finishes developing at the age of six, and the precise time of completion of development also depends on the horse's size (therefore a connection to breed exists), gender, and the quality of care provided by its owner. Also, if the horse is larger, its bones are larger; therefore, not only do the bones take longer to actually form bone tissue (bones are made of cartilage in earlier stages of bone formation), but the epiphyseal plates (plates that fuse a bone into one piece by connecting the bone shaft to the bone ends) are also larger and take longer to convert from cartilage to bone as well. These plates convert after the other parts of the bones do but are crucial to development.^[35]

Depending on maturity, breed and the tasks expected, young horses are usually put under saddle and trained to be ridden between the ages of two and four.^[36] Although Thoroughbred race horses are put on the track at as young as two years old in some countries,^[37] horses specifically bred for sports such as dressage are generally not entered into top-level competition until a minimum age of four years old, because their bones and muscles are not solidly developed, nor is their advanced training complete.^[38] For endurance riding competition, horses may not compete until they are a full 60 calendar months (5 years) old.^[6]

Anatomy

Main article: Equine anatomy

See also: Muscular system of the horse, Respiratory system of the horse, and Circulatory system of the horse

Skeletal system

Main article: Skeletal system of the horse

The skeletal system of a modern horse.

Horses have, on average, a skeleton of 205 bones.^[39] A significant difference in the bones contained in the horse skeleton, as compared to that of a human, is the lack of a collarbone. A 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, interesting 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 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 and hair, bone, tendons, ligaments, cartilage, and the assorted specialized tissues that make up the hoof (see section hooves, below).^[40]

Digestion

Main articles: Horse anatomy#Digestive system and Equine nutrition

Horses are herbivores with a digestive system adapted to a forage diet of grasses and other plant material, consumed regularly throughout the day, and so they have a relatively small stomach but very long intestines to facilitate a steady flow of nutrients. A 1,000 pounds (450 kg) horse will eat 15 to 25 pounds (6.8 to 11 kg) of food per day and, under normal use, drink 10 US gallons (38 L) to 12 US gallons (45 L) 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," that food goes through before reaching the large intestine. Unlike humans, horses cannot vomit, so digestion problems can quickly spell trouble, with colic a leading cause of death.^[41]

Teeth

Main article: Horse teeth

The incisors of a horse.

Horses are adapted to grazing. In an adult horse, there are 12 incisors (six upper and six lower), 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.^[42]

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, and while the diet and veterinary care of the horse can affect the rate of tooth wear, a very rough estimate of the age of a horse can be made by looking at its teeth.^[4]

Hooves

Main article: Horse hoof

See also: Horseshoe and Farrier

The critical importance of the feet and legs is summed up by the traditional adage, "no foot, no horse."^[43] 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, with the exterior hoof wall and horn of the sole made essentially of the same material as a human fingernail.^[44] The end result is that a horse, weighing on average 1,100 pounds (500 kg),^[45] travels on the same bones as a human on tiptoe.^[46] 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, just like a large fingernail, and needs to be trimmed (and horseshoes reset, if used) every five to eight weeks.^[47]

Senses

See also: Equine vision

A horse's eye

The senses of a horse are generally superior to those of a human. As prey animals, they must be aware of their surroundings at all times.^[48] They have very large eyes (among land animals only the ostrich has a larger eye), and the side positioning of the eyes gives the horse a wide field of vision of about 350°.^[49] 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.^[50]

Their hearing is good,^[48] and the pinna of each ear can rotate up to 180°, giving the potential for 360° hearing without having to move the head.^[51] Their sense of smell, while much better than that of humans, is not their strongest asset; they rely to a greater extent on vision.^[48]

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).^[52] 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,^[53] sensing contact as subtle as an insect landing anywhere on the body.^[54]

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,^[55] 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.^[56]

Gaits

The gallop

Main articles: Horse gait, Trot (horse gait), Canter, and Ambling

All horses move naturally with four basic gaits: the four-beat walk, the two-beat trot or jog, and the leaping gaits known as the canter or lope (a three-beat gait), and the gallop.^[57] Besides these basic gaits, some horses perform a two-beat pace, instead of the trot.^[58] 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.^[59] Ambling gaits are often genetic traits in specific breeds, often referred to as gaited horses.^[60] In most cases, gaited horses replace the standard trot, a 2-beat gait, with one of the four beat gaits.^[61]

Behavior

Main articles: Horse behavior and Stable vices

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. However, most light horse riding breeds were developed for speed, agility, alertness and endurance; natural qualities that extend from their wild ancestors.^[62] Horses are herd animals, with a clear hierarchy of rank, led by a dominant animal (usually a mare). Horses 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. However, 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.^[63] When confined with insufficient companionship, exercise or stimulation, horses 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.^[64]

Sleep patterns

See also: Horse sleep patterns and Sleep in non-humans

When horses lie down to sleep, others in the herd remain standing, awake or in a light doze, in order to keep watch.

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. ^[65] Horses sleep better when in groups because some animals will sleep while others stand guard to watch for predators. A horse kept entirely alone will not sleep well because its instincts are to keep a constant eye out for danger.^[66]

Unlike humans, horses do not sleep in a solid, unbroken period of time, but through 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.^[66] Most of this sleep occurs in many short intervals of about 15 minutes each.^[67]

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.^[66] 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.^[68] This condition differs from narcolepsy, though horses may also suffer from that disorder.^[69]

Temperament

See also: Horse behavior

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 description, used to describe temperament, not body temperature. For example, the "hot-bloods", such as race horses, exhibit more sensitivity and energy, while the "cold-bloods," such as most draft breeds, are quieter, calmer creatures.^[70]

Thoroughbred race horses are a "hot blooded" breed

"Hot" bloods

The "hot blooded" breeds include "oriental" breeds such as the Akhal-Teke, Barb, Arabian horse and the now-extinct Turkoman horse, as well as the Thoroughbred, a breed developed from the older oriental breeds. These five breeds are the only breeds given the classification of "hot blooded" today. The original hot bloods were brought to Europe from the Middle East and Northern Africa when European breeders wished to infuse characteristic traits into their best racing and light cavalry horses.^[71]

Hot bloods have a level of intelligence that allows them to be athletic, versatile, and learn quickly. They are bred for agility and speed and are generally considered spirited and bold.^[71] They tend to be thin-skinned, long-legged and slim in build; more physically refined than other types.^[72]

"Cold" bloods

Main article: Draft horse

The Brabant is an example of a "cold blooded" draft breed.

Muscular and heavy draft horses are known as "cold bloods," as they have been bred not only for strength, but also to have the calm, steady, patient temperament needed to pull a plow or a heavy carriage full of people. They are sometimes nicknamed "gentle giants" because of their placid dispositions. The "cold-blooded" group includes some pony breeds.^[73]

There are well over a dozen well-known draft breeds, and many more rarer breeds developed in various regions of the world that were adapted to local conditions. Some breeds are lighter and livelier, developed to pull carriages or to plow large fields in drier climates. Others are slower and more powerful, bred to plow fields with heavy, clay-based soils. One of the most common draft breeds is the Belgian. The largest is the Shire. Clydesdales, with their common coloration of a bay or black coat, with white legs and long-haired, "feathered" fetlocks, are one of the most easily recognized.^[74]

A modern "Warmblood" horse is large, but agile and athletic

Warmbloods

Main article: Warmblood

The term "warmblood" has two different meanings today; the more common modern meaning refers to a specific subset of horse breeds, and the other, older meaning refers simply to horses of a moderate temperament. The term "warm blood," up through approximately the 1970s, originally referred to any cross of "cold blooded" draft horses on "hot blooded" Thoroughbreds or Arabians. Examples included breeds such as the Irish Draught horse or the Cleveland Bay, and sometimes also referred to the "Baroque horses" used for classical dressage, such as the Lipizzan or Andalusian. Sometimes the term was even used to refer to breeds of light riding horse other than Thoroughbreds or Arabians, such as the Morgan horse.^[75]

Today the term "warmblood" usually refers to a group of sport horse breeds that have dominated the Olympic Games and World Equestrian Games in Dressage and Show Jumping since the 1960s. The "Warmblood" breeds began when European carriage and war horses were crossed with Arabians or Thoroughbreds, producing a tall riding horse with more refinement than a draft horse, but greater size and more phlegmatic temperament than a lighter breed.^[76] Certain pony breeds with warmblood characteristics have been developed for smaller riders.^[77]

Breeds

Main articles: List of horse breeds, Horse breeding, and Selective breeding

Horse breeds are groups of horses with distinctive characteristics, such as conformation, color, performance, intelligence or disposition, that are transmitted consistently to their offspring. These inherited traits are usually the result of a combination of natural crosses and artificial selection methods aimed at developing horses for specific tasks. Certain breeds are known for certain talents, for example, Standardbreds are known for their speed in harness. 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 with a tremendous influence. There are more than 300 horse breeds in the world today.^[78]

Origin of breeds

See also: Domestication of the horse

Different schools of thought exist to explain how this range of size and shape came about. One school, which some refer to as the "Four Foundations", (see The Four Foundations theory below), suggests that the modern horse evolved from multiple types of early wild pony and horse prototypes, each adapted to a given habitat, and the differences between these types account for some of the differences in type of the modern breeds. ^[79] An older school of thought holds only one type of wild horse underwent domestication, and it diverged in form after domestication through human selective breeding (or in the case of feral horses and landraces, through ecological pressures).^[80] However, modern DNA evidence suggests that domesticated horses evolved from multiple wild populations, instead of only one.^[81]

In either case, modern horse breeds developed in response to the need for "form to function"; that is, the necessity to develop certain physical characteristics necessary to perform a certain type of work.^[82] Thus, powerful but refined horses such as the Andalusian or the Lusitano developed in Spain and Portugal as riding horses that also had a great aptitude for dressage,^[83] 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.^[84] Ponies of all breeds developed mainly out of a need for a horse that could fulfill specific local draft and transportation needs while surviving in harsh environments, but in the 20th century many pony breeds had Arabian and other blood added to make a more refined pony suitable for riding.^[85] Other breeds were developed that were specifically meant for light agricultural work, heavy and light carriage and road work, various equestrian disciplines or simply pets.^[82]

Purebreds and registries

Main articles: Breed registry and Purebred

Selective breeding of horses has occurred as long as humans have domesticated them. However, the concept of purebred bloodstock and a controlled breed registry has only gained wide importance in modern times. 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.^[86]

An example of early selective breeding were the Bedouin people, who had a reputation for careful breeding practices, keeping extensive pedigrees of their Arabian horses and placing great value upon pure, or "asil" bloodlines.^[87] Though these pedigrees were originally transmitted via an oral tradition, written pedigrees of Arabian horses can be found that date to the 14th century.^[88] 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.^[89] One of the earliest formal registries was General Stud Book for Thoroughbreds, which was begun in 1791 and traced back to the Arabian stallions imported to England from the Middle East that became the foundation stallions for the breed.^[90]

Today, breed designation varies. 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.^[91][92] 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, and must also exhibit specific color characteristics.^[93] 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.^[94]

Others, such as most of the warmblood breeds used in sport horse disciplines, have an open stud book to varying degrees. While pedigree is considered, outside bloodlines are admitted to the registry if the horses meet the standard. These registries usually require a studbook selection process involving individual judging of an individual animal's quality, performance, and conformation before registration is finalized.^[95] A few "registries," particularly some color breed registries, are very open, and will allow membership of any horse that meets a certain criteria, such as coat color, regardless of pedigree or conformation.^[96]

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 (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.^[91] 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 take away the risk of injury during mating.^[97] 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.^[98]

Regional specialization

Some countries specialize in breeding horses suitable for particular activities. For example, Australia, the United States, and the Patagonia region of South America are known for breeding horses particularly suitable for working cattle and other livestock.^[99] Spain and Portugal are known for the Iberian horse breeds used in dressage and bullfighting.^[83] Austria is known worldwide for its Lipizzaner horses, used for dressage and high school work in the famous Spanish Riding School in Vienna.^[100] The United Kingdom breeds an array of heavy draft horses and several breeds of hardy ponies.^[101] Russia takes great pride in breeding harness racing horses, a tradition dating back to the development of the Orlov Trotter in the 18th century.^[102]

Evolution

Mesohippus, an ancestor of the modern horse

Main article: Evolution of the horse

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.^[103] 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—have survived to the present day, with 18 known species existing.^[104] 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.^[105] The extra toe on the front feet soon disappeared with the Mesohippus, which lived 32 to 37 million years ago,^[106] and by about 5 million years ago, the modern Equus had developed.^[107] The extra side toes shrank in size until they have vanished in modern horses. All that remains are a set of small vestigial bones on the leg above the hoof,^[108] known informally as ergots, chestnuts, or splint bones.^[109] Their legs also lengthened as their toes disappeared and until they were a hoofed animal capable of running at great speed.^[108]

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.^[110]

Domestication and surviving wild species

Main article: Domestication of the horse

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.^[111] It is thought that the horse was completely domesticated by 3000 B.C., and by 2000 B.C. 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.^[112]

The "Four Foundations" theory

There is a theory that there were four basic "proto" horses that developed with adaptations to their environment prior to domestication^[113]There are competing theories, some arguing that the prototypes were separate species, others suggesting that the prototypes were physically different manifestations of the same species. Either way, the most common theories of historical wild species from which other types are thought to have developed suggests the following base prototypes:

Przewalski's Horse, the last surviving wild horse species

• The "Warmblood" subspecies or "Forest Horse": (Equus ferus silvaticus, also called the Diluvial Horse) thought to have evolved into Equus ferus germanicus, and which may have contributed to the development of the warmblood horses of northern Europe, as well as older "heavy horses" such as the Ardennais.
• The "Draft" subspecies: a small, sturdy, heavyset animal with a heavy hair coat, arising in northern Europe, adapted to cold, damp climates, somewhat resembling today's draft horse and even the Shetland pony.
• The "Oriental" subspecies: a taller, slim, refined and agile animal arising in western Asia, adapted to hot, dry climates, thought to be the progenitor of the modern Arabian horse and Akhal-Teke.
• The "Tarpan" subspecies: dun-colored, sturdy animal, the size of a large pony, adapted to the cold, dry climates of northern Asia, the predecessor to the Tarpan and Przewalski's Horse as well as the domesticated Mongolian horse.^[113]

Wild species surviving into modern times

Main article: Wild horse

There is only one true wild horse alive today. Most "wild" horses today are actually feral horses, animals that escaped or were turned loose from domestic herds and the descendants of those animals.^[114] 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 form 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 was a complete success, but all three resulted in horses with many similarities to the Tarpan.^[115]

Przewalski's Horse (Equus ferus przewalskii), a rare Asian species, is the only true wild horse alive today. Also known as the Mongolian Wild Horse, Mongolians know it as the taki, while the Kyrgyz people call it a kirtag. Small wild breeding populations of this animal, named after the Russian explorer Przewalski, exist in Mongolia.^[116] There are also small populations maintained at zoos throughout the world. The species was for a time extinct in the wild between 1969 and 1992 but due to conservations efforts by numerous zoos, a small breeding population of Przewalksi's Horse was reestablished in the wild.^[117]

Feral populations

Main article: Feral horse

Free-roaming Mustangs on BLM land cir. 2007

Feral horses, who had domesticated ancestors but were born and live in the wild, are distinct from wild animals, whose ancestors have never undergone domestication.^[114] Many populations of feral horses exist throughout the world.^[118][119] Studies of feral herds have provided useful insights into the behavior of prehistoric horses,^[120] as well as greater understanding of the instincts and behaviours that drive tame horses.^[121]

Other modern equids

Main article: Equidae

Besides the horse, there are seven other species in the genus of equus, in the equidae family. These are the ass or donkey, Equus asinus; the Mountain zebra, Equus zebra; Burchell's zebra, Equus burchelli; Grevy's zebra, Equus grevyi; the Kiang, Equus kiang; Quagga, Equus quagga and the Kulan, Equus hemionus, including its subspecies, the Onager, Equus hemionus onager.^[122]

Horses can crossbreed with other members of the equus genus. The most common hybrid is the mule, a cross between a "jack" - a male donkey - and a mare. A related hybrid, a hinny, is a cross between a stallion and jenny - a female donkey.^[123] Other hybrids include the zorse, a cross between a zebra and a horse that is often created in Africa and used for trekking on Mount Kenya.^[124] With rare exceptions, most hybrids are sterile and cannot reproduce.^[125]

Interaction with humans

Horse headcount in 2003

Around the world, horses play a role within human economies. The FAO reports that in 2003, China had the largest number of horses in the world with over 8 million horses, followed by Mexico (6,260,000), Brazil (5,900,500), the United States (5,300,000), and Argentina (3,655,000).^[126] Horses are used for leisure activities, sports, and working purposes. 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.^[127] 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.^[128]

Sport

Main articles: Equestrianism, Horse racing, and Horse training

Since the Iron Age, equestrians have 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.^[129] 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 tack for each sport. The continuing 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.^[130]

A horse performing a dressage test

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.^[131] 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 classes where the horses are led (rather than ridden) to exhibit their presence, conformation and manners. The method of judging classes varies depending on the discipline, but is usually dependent on style and ability of both horse and rider.^[132] 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.^[133] Examples of these sports of partnership between human and animal also include jousting (reenacting the skills used by medieval knights), where the main goal is for one rider to dismount the other,^[134] and buzkashi, a team game played throughout Central Asia, the aim being to capture a goat carcass while on horseback.^[133]

Horse racing is an equestrian sport that doubles as a huge international industry and is seen in almost every nation in 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.^[135] A major part of the economic importance of horse racing lies in the gambling associated with it.^[136]

Work

A mounted police officer in Poland.

There are certain jobs that horses do very well, and no amount of technology appears able to supersede. Mounted police horses are still effective for crowd control.^[137] Cattle ranches still require riders on horseback to round up cattle that are scattered across remote, rugged terrain.^[138] Search and rescue organizations in some countries depend upon mounted teams to locate people, particularly hikers and children, and to provide disaster relief assistance.^[139] Horses can also be used in other areas where it is necessary to avoid vehicular disruption to delicate soil. Examples include areas such as a nature reserve. They may also be the only form of transport allowed in wilderness areas. They are also quieter than motorized vehicles. Peace 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.^[140]

Some land management practices such as cultivating and logging can be efficiently performed with horses. In agriculture, less use of fossil fuels, reduced soil compaction, and less damage to soil structure can be seen over time with the use of draft animals such as horses.^[141] 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.^[142] 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 including Morocco, Kenya and Guatemala.^[143]

Entertainment and culture

See also: Horses in art and Horse worship

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, and especially famous battles.^[144] 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 VIPs to and from certain culturally significant events.^[145] Exhibitions are another example, such as the Budweiser Clydesdales, a team of draft horses seen in parades and other public settings that pull a beer wagon similar to that used prior to the invention of the modern motorized truck.^[146]

Horses are frequently used in television and motion pictures to add authenticity to historical dramas as well as adding charm to films set in modern-day, or even futuristic science fiction settings.^[147] Both live horses and iconic images of horses are used in advertising to promote a variety of products.^[148]

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.^[149] The horse features in the 12-year cycle of animals which appear 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.^[150]

Assisted learning and therapy

See also: Hippotherapy, Therapeutic horseback riding, and Equine Assisted Learning

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.^[151] 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.^[152] 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.^[153]

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.^[154] Equine Assisted Learning (EAL) (also known as equine guided education or equine assisted professional development) is field of experiential learning for corporate, professional and personal development.^[155] 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.^[156]

Warfare

A modern reenactment of a cavalry charge

Main article: Horses in warfare

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 4000BC,^[157] and the use of horses in warfare was widespread by the end of the Bronze Age.^[158] While 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 Darfur conflict.^[159]

Products

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.^[160] 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.^[160] 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.^[161] The tail hair of horses can be used for making bows for stringed instruments such as the violin, viola, cello, and double bass.^[162]

Horsemeat 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.^[163] Horsemeat has been an export industry in the United States and other countries,^[163] though legislation has periodically been introduced in the United States Congress which would end export from the United States.^[164] Horsehide leather has been used for boots, gloves, jackets,^[165] baseballs,^[166]and baseball gloves. Horsehide and horse hooves can also be used to produce animal glue.^{[dead link][167]} Horse bones can be used to make implements.^[168] 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.^[169] In Asia, the saba is a horsehide vessel used in the production of kumis.^[170]

Care

Main article: Horse care

See also: Equine nutrition, Horse grooming, Veterinary medicine, and Farrier

Domesticated horses require ongoing attention from human caretakers

Horses are grazing animals, and their major source of nutrients is good-quality forage from hay or pasture.^[171] They can consume approximately 2% to 2.5% of their body weight in dry feed each day. Therefore, a 1,000 lb (450 kg) adult horse could eat up to 25 lb (11 kg) of food.^[172] Sometimes, concentrated feed such as grain is fed in addition to pasture or hay, especially when the animal is very active.^[173] When grain is fed, equine nutritionists recommend that 50% or more of the animal's diet by weight should still be forage.^[174]

Horses require a plentiful supply of clean water, a minimum of 10 US gallons (38 L) to 12 US gallons (45 L) per day.^[175] 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.^[176]

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.^[177] If horses are kept inside in a barn, they require regular daily exercise for their physical health and mental well-being.^[178] When turned outside, they require well-maintained, sturdy fences to be safely contained.^[179] Regular grooming is also helpful to help the horse maintain good health of the hair coat and underlying skin.^[180]

Riding and driving

Main articles: Equestrianism, Driving (horse), and Horse tack

Horses are usually ridden with a saddle on their backs to assist the rider with balance and positioning, and a bridle on their heads to assist the rider in maintaining control.^[181] Sometimes horses are ridden without a saddle,^[182] and occasionally, horses are trained to perform without a bridle or other headgear.^[183] Many horses are also driven, which requires a harness, bridle and some type of vehicle^[184] Communication between human and horse is paramount in any activity.^[129]

From the time the horse was domesticated, a wide variety of riding methods or styles have developed, all of which balance the need to allow the horse freedom of movement in activities such as horse racing or show jumping against the need for security and comfort for the rider, precision of commands, and overall control. Worldwide, the most common modern riding style is referred to in the United States as English riding, which is a broad style that encompasses most Olympic Equestrian competition, and includes such specific styles as dressage, hunt seat, show jumping and saddle seat, among many others. Western riding is a popular style seen in North America, derived from the traditions of Spain, modified to fit the needs of cattle ranchers. A similar riding style is seen with the Stockman of Australia.^{[citation needed]}