Horse

Conservation status

Domesticated

Scientific classification

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Perissodactyla

Family: Equidae

Genus: Equus

Species: E. ferus

Subspecies: E. f. caballus

Trinomial name

Equus ferus caballusLinnaeus, 1758[1]

Synonyms

at least 48 published[2]

HorseFrom Wikipedia, the free encyclopedia

For other uses, see Horse (disambiguation).

The horse (Equus ferus caballus)[2][3] is one of two extantsubspecies of Equus ferus. It is an odd-toed ungulate mammalbelonging to the taxonomic family Equidae. The horse has evolvedover the past 45 to 55 million years from a small multi-toedcreature, Hyracotherium, into the large, single-toed animal of today.Humans began to domesticate horses around 4000 BC, and theirdomestication is believed to have been widespread by 3000 BC.Horses in the subspecies caballus are domesticated, although somedomesticated populations live in the wild as feral horses. Theseferal populations are not true wild horses, as this term is used todescribe horses that have never been domesticated, such as theendangered Przewalski's horse, a separate subspecies, and the onlyremaining true wild horse. There is an extensive, specializedvocabulary used to describe equine-related concepts, coveringeverything from anatomy to life stages, size, colors, markings,breeds, locomotion, and behavior.

Horses' anatomy enables them to make use of speed to escapepredators and they have a well-developed sense of balance and astrong fight-or-flight response. Related to this need to flee frompredators in the wild is an unusual trait: horses are able to sleepboth standing up and lying 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. Mostdomesticated horses begin training under saddle or in harnessbetween the ages of two and four. They reach full adultdevelopment by age five, and have an average lifespan of between25 and 30 years.

Horse breeds are loosely divided into three categories based ongeneral temperament: spirited "hot bloods" with speed andendurance; "cold bloods", such as draft horses and some ponies,suitable for slow, heavy work; and "warmbloods", developed fromcrosses between hot bloods and cold bloods, often focusing oncreating breeds for specific riding purposes, particularly in Europe.There are more than 300 breeds of horse in the world today,developed for many different uses.

Horses and humans interact in a wide variety of sport competitionsand non-competitive recreational pursuits, as well as in working activities such as police work, agriculture,entertainment, and therapy. Horses were historically used in warfare, from which a wide variety of riding and

driving techniques developed, using many different styles of equipment and methods of control. Many productsare derived from horses, including meat, milk, hide, hair, bone, and pharmaceuticals extracted from the urine ofpregnant mares. Humans provide domesticated horses with food, water and shelter, as well as attention fromspecialists such as veterinarians and farriers.

Contents1 Biology

1.1 Lifespan and life stages1.2 Size and measurement

1.2.1 Ponies

1.3 Genetics

1.4 Colors and markings

1.5 Reproduction and development1.6 Anatomy

1.6.1 Skeletal system

1.6.2 Hooves

1.6.3 Teeth

1.6.4 Digestion

1.6.5 Senses

1.7 Movement1.8 Behavior

1.8.1 Intelligence and learning

1.8.2 Temperament

1.8.3 Sleep patterns2 Taxonomy and evolution

2.1 Wild species surviving into modern times

2.2 Other modern equids3 Domestication

3.1 Feral populations

3.2 Breeds

Points of a horse[4][5]

3.2 Breeds4 Interaction with humans

4.1 Sport

4.2 Work

4.3 Entertainment and culture

4.4 Therapeutic use

4.5 Warfare

4.6 Products

4.7 Care

5 See also

6 References

7 Sources

8 Further reading

9 External links

BiologyMain article: Equine anatomy

Specific terms and specialized language are used todescribe equine anatomy, different life stages, colorsand breeds.

Lifespan and life stages

Depending on breed, management and environment,the modern domestic horse has a life expectancy of 25to 30 years.[6] Uncommonly, a few animals live intotheir 40s and, occasionally, beyond.[7] The oldestverifiable record was "Old Billy", a 19th-century horsethat lived to the age of 62.[6] In modern times, SugarPuff, who had been listed in Guinness World Recordsas the world's oldest living pony, died in 2007 at age56.[8]

Regardless of a horse or pony's actual birth date, for most competition purposes a year is added to its age eachJanuary 1 of each year in the Northern Hemisphere[6][9] and each August 1 in the Southern Hemisphere.[10] Theexception is in endurance riding, where the minimum age to compete is based on the animal's actual calendarage.[11]

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

Colt: A male horse under the age of four.[12] A common terminology error is to call any young horse a"colt", when the term actually only refers to young male horses.[13]

Filly: A female horse under the age of four.[14]

Foal: A horse of either sex less than one year old. A nursing foal is sometimes called a suckling and a foalthat has been weaned is called a weanling.[14] Most domesticated foals are weaned at five to sevenmonths of age, although foals can be weaned at four months with no adverse physical effects.[15]

Gelding: A castrated male horse of any age.[14]

Mare: A female horse four years old and older.[16]

Stallion: A non-castrated male horse four years old and older.[17] The term "horse" is sometimes usedcolloquially to refer specifically to a stallion.[18]

Yearling: A horse of either sex that is between one and two years old.[19]

In horse racing, these definitions may differ: For example, in the British Isles, Thoroughbred horse racingdefines colts and fillies as less than five years old.[20] However, Australian Thoroughbred racing defines coltsand fillies as less than four years old.[21]

Size and measurement

The height of horses is usually measured at the highest point of the withers, where the neck meets the back.[22]

This point is used because it is a stable point of the anatomy, unlike the head or neck, which move up and downin relation to the body of the horse.

In English-speaking countries, the height of horses is often stated in units of hands and inches: one hand is equalto 4 inches (101.6 mm). The height is expressed as the number of full hands, followed by a point, then thenumber of additional inches, and ending with the abbreviation "h" or "hh" (for "hands high"). Thus, a horsedescribed as "15.2 h" is 15 hands plus 2 inches, for a total of 62 inches (157.5 cm) in height.[23]

The size of horses varies by breed, but also is influenced by nutrition. Light riding horses usually range inheight from 14 to 16 hands (56 to 64 inches, 142 to 163 cm) and can weigh from 380 to 550 kilograms (840 to1,210 lb).[24] Larger riding horses usually start at about 15.2 hands (62 inches, 157 cm) and often are as tall as17 hands (68 inches, 173 cm), weighing from 500 to 600 kilograms (1,100 to 1,320 lb).[25] Heavy or drafthorses are usually at least 16 hands (64 inches, 163 cm) high and can be as tall as 18 hands (72 inches, 183 cm)high. They can weigh from about 700 to 1,000 kilograms (1,540 to 2,200 lb).[26]

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

The largest horse in recorded history was probably a Shire horse named Mammoth, who was born in 1848. Hestood 21.21⁄2 hands (86.5 inches, 220 cm) high and his peak weight was estimated at 1,500 kilograms

(3,300 lb).[27] The current record holder for the world's smallest horse is Thumbelina, a fully mature miniaturehorse affected by dwarfism. She is 17 in (43 cm) tall and weighs 57 lb (26 kg).[28]

Ponies

Main article: Pony

Ponies are taxonomically the same animals as horses. Thedistinction between a horse and pony is commonly drawnon the basis of height, especially for competition purposes.However, height alone is not dispositive; the differencebetween horses and ponies may also include aspects ofphenotype, including conformation and temperament.

The traditional standard for height of a horse or a pony atmaturity is 14.2 hands (58 inches, 147 cm). An animal14.2 h or over is usually considered to be a horse and oneless than 14.2 h a pony,[29] but there are many exceptionsto the traditional standard. In Australia, ponies areconsidered to be those under 14 hands (56 inches,142 cm),[30] For competition in the Western division ofthe United States Equestrian Federation, the cutoff is14.1 hands (57 inches, 145 cm)[31] The International

Federation for Equestrian Sports, the world governing body for horse sport, uses metric measurements anddefines a pony as being any horse measuring less than 148 centimetres (58.27 in) at the withers without shoes,which is just over 14.2 h, and 149 centimetres (58.66 in), or just over 14.2½ h, with shoes.[32]

Height is not the sole criterion for distinguishing horses from ponies. Breed registries for horses that typicallyproduce individuals both under and over 14.2 h consider all animals of that breed to be horses regardless of theirheight.[33] Conversely, some pony breeds may have features in common with horses, and individual animalsmay occasionally mature at over 14.2 h, but are still considered to be ponies.[34]

Ponies often exhibit thicker manes, tails, and overall coat. They also have proportionally shorter legs, widerbarrels, heavier bone, shorter and thicker necks, and short heads with broad foreheads. They may have calmertemperaments than horses and also a high level of equine intelligence that may or may not be used to cooperatewith human handlers.[29] Small size, by itself, is not an exclusive determinant. For example, the Shetland ponywhich averages 10 hands (40 inches, 102 cm), is considered a pony.[29] Conversely, breeds such as the Falabellaand other miniature horses, which can be no taller than 30 inches (76 cm), are classified by their registries asvery small horses, not ponies.[35]

Genetics

Bay (left) and chestnut (sometimes called "sorrel") aretwo of the most common coat colors, seen in almostall breeds.

Horses have 64 chromosomes.[36] The horse genome was sequenced in 2007. It contains 2.7 billion DNA basepairs,[37] which is larger than the dog genome, but smaller than the human genome or the bovine genome.[38]

The map is available to researchers.[39]

Colors and markings

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

Horses exhibit a diverse array of coat colors anddistinctive markings, described by a specializedvocabulary. Often, a horse is classified first by its coatcolor, before breed or sex.[40] Horses of the same colormay be distinguished from one another by whitemarkings,[41] which, along with various spotting patterns,are inherited separately from coat color.[42]

Many genes that create horse coat colors and patterns havebeen identified. Current genetic tests can identify at least13 different alleles influencing coat color,[43] and researchcontinues to discover new genes linked to specific traits.The basic coat colors of chestnut and black are determined by the gene controlled by the Melanocortin 1receptor,[44] also known as the "extension gene" or "red factor,"[43] as its recessive form is "red" (chestnut) andits dominant form is black.[45] Additional genes control suppression of black color to point coloration thatresults in a bay, spotting patterns such as pinto or leopard, dilution genes such as palomino or dun, as well asgraying, and all the other factors that create the many possible coat colors found in horses.[43]

Horses which have a white coat color are often mislabeled; a horse that looks "white" is usually a middle-agedor older gray. Grays are born a darker shade, get lighter as they age, but usually keep black skin underneaththeir white hair coat (with the exception of pink skin under white markings). The only horses properly calledwhite are born with a predominantly white hair coat and pink skin, a fairly rare occurrence.[45] Different andunrelated genetic factors can produce white coat colors in horses, including several different alleles of dominantwhite and the sabino-1 gene.[46] However, there are no "albino" horses, defined as having both pink skin and redeyes.[47]

Reproduction and development

Main article: Horse breeding

Gestation lasts approximately 340 days, with an average range 320–370 days,[48] and usually results in one foal;twins are rare.[49] Horses are a precocial species, and foals are capable of standing and running within a shorttime following birth.[50] Foals are usually born in the spring. The estrous cycle of a mare occurs roughly every

The skeletal system of a modern horse

19–22 days and occurs from early spring into autumn. Most mares enter an anestrus period during the winterand thus do not cycle in this period.[51] Foals are generally weaned from their mothers between four and sixmonths of age.[52]

Horses, particularly colts, sometimes are physically capable of reproduction at about 18 months, butdomesticated horses are rarely allowed to breed before the age of three, especially females.[53] Horses fouryears old are considered mature, although the skeleton normally continues to develop until the age of six;maturation also depends on the horse's size, breed, sex, and quality of care. Larger horses have larger bones;therefore, not only do the bones take longer to form bone tissue, but the epiphyseal plates are larger and takelonger to convert from cartilage to bone. These plates convert after the other parts of the bones, and are crucialto development.[54]

Depending on maturity, breed, and work expected, horses are usually put under saddle and trained to be riddenbetween the ages of two and four.[55] Although Thoroughbred race horses are put on the track as young as theage of two in some countries,[56] horses specifically bred for sports such as dressage are generally not put undersaddle until they are three or four years old, because their bones and muscles are not solidly developed.[57] Forendurance riding competition, horses are not deemed mature enough to compete until they are a full 60 calendarmonths (five years) old.[11]

Anatomy

Main articles: Equine anatomy, Muscular system of the horse, Respiratory system of the horse andCirculatory system of the horse

Skeletal system

Main article: Skeletal system of the horse

The horse skeleton averages 205 bones.[58] A significantdifference between the horse skeleton and that of a humanis the lack of a collarbone—the horse's forelimbs areattached to the spinal column by a powerful set ofmuscles, tendons, and ligaments that attach the shoulderblade to the torso. The horse's legs and hooves are alsounique structures. Their leg bones are proportioneddifferently from those of a human. For example, the bodypart that is called a horse's "knee" is actually made up ofthe carpal bones that correspond to the human wrist.Similarly, the hock contains bones equivalent to those inthe human ankle and heel. The lower leg bones of a horsecorrespond to the bones of the human hand or foot, andthe fetlock (incorrectly called the "ankle") is actually theproximal sesamoid bones between the cannon bones (a

single equivalent to the human metacarpal or metatarsal bones) and the proximal phalanges, located where onefinds 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.[59]

Hooves

Main articles: Horse hoof, Horseshoe and Farrier

The critical importance of the feet and legs is summed up by the traditional adage, "no foot, no horse".[60] Thehorse hoof begins with the distal phalanges, the equivalent of the human fingertip or tip of the toe, surroundedby cartilage and other specialized, blood-rich soft tissues such as the laminae. The exterior hoof wall and hornof the sole is made of keratin, the same material as a human fingernail.[61] The end result is that a horse,weighing on average 500 kilograms (1,100 lb),[62] travels on the same bones as would a human on tiptoe.[63]

For the protection of the hoof under certain conditions, some horses have horseshoes placed on their feet by aprofessional farrier. The hoof continually grows, and in most domesticated horses needs to be trimmed (andhorseshoes reset, if used) every five to eight weeks,[64] though the hooves of horses in the wild wear down andregrow at a rate suitable for their terrain.

Teeth

Main article: Horse teeth

Horses are adapted to grazing. In an adult horse, there are 12 incisors at the front of the mouth, adapted to bitingoff the grass or other vegetation. There are 24 teeth adapted for chewing, the premolars and molars, at the backof the mouth. Stallions and geldings have four additional teeth just behind the incisors, a type of canine teethcalled "tushes". Some horses, both male and female, will also develop one to four very small vestigial teeth infront 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 gums,or "bars" of the horse's mouth when the horse is bridled.[65]

An estimate of a horse's age can be made from looking at its teeth. The teeth continue to erupt throughout lifeand are worn down by grazing. Therefore, the incisors show changes as the horse ages; they develop a distinctwear pattern, changes in tooth shape, and changes in the angle at which the chewing surfaces meet. This allowsa very rough estimate of a horse's age, although diet and veterinary care can also affect the rate of tooth wear.[6]

Digestion

Main articles: Equine digestive system and Equine nutrition

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 stomachbut very long intestines to facilitate a steady flow of nutrients. A 450-kilogram (990 lb) horse will eat 7 to 11kilograms (15 to 24 lb) of food per day and, under normal use, drink 38 to 45 litres (8.4 to 9.9 imp gal; 10 to12 US gal) of water. Horses are not ruminants, they have only one stomach, like humans, but unlike humans,

A horse's eye

they can utilize cellulose, a major component of grass. Horses are hindgut fermenters, Cellulose fermentation bysymbiotic bacteria occurs in the cecum, or "water gut", which food goes through before reaching the largeintestine. Horses cannot vomit, so digestion problems can quickly cause colic, a leading cause of death.[66]

Senses

See also: Equine vision

The horses' senses are based on their status as prey animals, where theymust be aware of their surroundings at all times.[67] They have thelargest eyes of any land mammal,[68] and are lateral-eyed, meaning thattheir eyes are positioned on the sides of their heads.[69] This means thathorses have a range of vision of more than 350°, with approximately 65°of this being binocular vision and the remaining 285° monocularvision.[68] Horses have excellent day and night vision, but they havetwo-color, or dichromatic vision; their color vision is somewhat like red-green color blindness in humans, where certain colors, especially red and related colors, appear as a shade ofgreen.[70]

Their sense of smell, while much better than that of humans, is not quite as good as that of a dog. It is believedto play a key role in the social interactions of horses as well as detecting other key scents in the environment.Horses have two olfactory centers. The first system is in the nostrils and nasal cavity, which analyze a widerange of odors. The second, located under the nasal cavity, are the Vomeronasal organs, also called Jacobson'sorgans. These have a separate nerve pathway to the brain and appear to primarily analyze pheromones.[71]

A horse's hearing is good,[67] and the pinna of each ear can rotate up to 180°, giving the potential for 360°hearing without having to move the head.[72] Noise impacts the behavior of horses and certain kinds of noisemay contribute to stress: A 2013 study in the UK indicated that stabled horses were calmest in a quiet setting, orif listening to country or classical music, but displayed signs of nervousness when listening to jazz or rockmusic. This study also recommended keeping music under a volume of 21 decibels.[73] An Australian studyfound that stabled racehorses listening to talk radio had a higher rate of gastric ulcers than horses listening tomusic, and racehorses stabled where a radio was played had a higher overall rate of ulceration than horsesstabled where there was no radio playing.[74]

Horses have a great sense of balance, due partly to their ability to feel their footing and partly to highlydeveloped proprioception—the unconscious sense of where the body and limbs are at all times.[75] A horse'ssense of touch is well developed. The most sensitive areas are around the eyes, ears, and nose.[76] Horses areable to sense contact as subtle as an insect landing anywhere on the body.[77]

Horses have an advanced sense of taste, which allows them to sort through fodder and choose what they wouldmost like to eat,[78] and their prehensile lips can easily sort even small grains. Horses generally will not eatpoisonous plants, however, there are exceptions; horses will occasionally eat toxic amounts of poisonous plantseven when there is adequate healthy food.[79]

The gallop

Movement

Main articles: Horse gait, Trot (horse gait), Canter andAmbling

All horses move naturally with four basic gaits: the four-beat walk, which averages 6.4 kilometres per hour(4.0 mph); the two-beat trot or jog at 13 to 19 kilometres perhour (8.1 to 11.8 mph) (faster for harness racing horses); thecanter or lope, a three-beat gait that is 19 to 24 kilometresper hour (12 to 15 mph); and the gallop.[80] The gallopaverages 40 to 48 kilometres per hour (25 to 30 mph),[81]

but the world record for a horse galloping over a short,sprint distance is 88 kilometres per hour (55 mph).[82]

Besides these basic gaits, some horses perform a two-beatpace, instead of the trot.[83] There also are several four-beat "ambling" gaits that are approximately the speed ofa trot or pace, though smoother to ride. These include the lateral rack, running walk, and tölt as well as thediagonal fox trot.[84] Ambling gaits are often genetic in some breeds, known collectively as gaited horses.[85]

Often, gaited horses replace the trot with one of the ambling gaits.[86]

Behavior

Main articles: Horse behavior and Stable vices

Horses are prey animals with a strong fight-or-flight response. Their first reaction to threat is to startle andusually flee, although they will stand their ground and defend themselves when flight is impossible or if theiryoung are threatened.[87] They also tend to be curious; when startled, they will often hesitate an instant toascertain the cause of their fright, and may not always flee from something that they perceive as non-threatening. Most light horse riding breeds were developed for speed, agility, alertness and endurance; naturalqualities that extend from their wild ancestors. However, through selective breeding, some breeds of horses arequite docile, particularly certain draft horses.[88]

Horses are herd animals, with a clear hierarchy of rank, led by a dominant individual, usually a mare. They arealso social creatures that 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, butwith training, horses can learn to accept a human as a companion, and thus be comfortable away from otherhorses.[89] However, when confined with insufficient companionship, exercise, or stimulation, individuals maydevelop stable vices, an assortment of bad habits, mostly stereotypies of psychological origin, that include woodchewing, wall kicking, "weaving" (rocking back and forth), and other problems.[90]

Intelligence and learning

Illustration of assorted breeds; slim, light hotbloods,medium-sized warmbloods and draft and pony-typecoldblood breeds

Studies have indicated that horses perform a number of cognitive tasks on a daily basis, meeting mentalchallenges that include food procurement and identification of individuals within a social system. They alsohave good spatial discrimination abilities.[91] Studies have assessed equine intelligence in areas such as problemsolving, speed of learning, and memory. Horses excel at simple learning, but also are able to use more advancedcognitive abilities that involve categorization and concept learning. They can learn using habituation,desensitization, classical conditioning, and operant conditioning, and positive and negative reinforcement.[91]

One study has indicated that horses can differentiate between "more or less" if the quantity involved is less thanfour.[92]

Domesticated horses may face greater mental challenges than wild horses, because they live in artificialenvironments that prevent instinctive behavior whilst also learning tasks that are not natural.[91] Horses areanimals of habit that respond well to regimentation, and respond best when the same routines and techniques areused consistently. One trainer believes that "intelligent" horses are reflections of intelligent trainers whoeffectively use response conditioning techniques and positive reinforcement to train in the style that best fitswith an individual animal's natural inclinations.[93]

Temperament

Main articles: Draft horse, Warmblood and Oriental horse

Horses are mammals, and as such are warm-blooded, or endothermic creatures, as opposed to cold-blooded, orpoikilothermic animals. However, these words have developed a separate meaning in the context of equineterminology, used to describe temperament, not body temperature. For example, the "hot-bloods", such as manyrace horses, exhibit more sensitivity and energy,[94] while the "cold-bloods", such as most draft breeds, arequieter and calmer.[95] Sometimes "hot-bloods" are classified as "light horses" or "riding horses",[96] with the"cold-bloods" classified as "draft horses" or "work horses".[97]

"Hot blooded" breeds include "oriental horses" such asthe Akhal-Teke, Arabian horse, Barb and now-extinctTurkoman horse, as well as the Thoroughbred, a breeddeveloped in England from the older orientalbreeds.[94] Hot bloods tend to be spirited, bold, andlearn quickly. They are bred for agility and speed.[98]

They tend to be physically refined—thin-skinned, slim,and long-legged.[99] The original oriental breeds werebrought to Europe from the Middle East and NorthAfrica when European breeders wished to infuse thesetraits into racing and light cavalry horses.[100][101]

Muscular, heavy draft horses are known as "coldbloods", as they are bred not only for strength, but alsoto have the calm, patient temperament needed to pull aplow or a heavy carriage full of people.[95] They aresometimes nicknamed "gentle giants".[102] Well-known

When horses lie down to sleep, othersin the herd remain standing, awake orin a light doze, keeping watch.

draft breeds include the Belgian and the Clydesdale.[102] Some, like the Percheron, are lighter and livelier,developed to pull carriages or to plow large fields in drier climates.[103] Others, such as the Shire, are slowerand more powerful, bred to plow fields with heavy, clay-based soils.[104] The cold-blooded group also includessome pony breeds.[105]

"Warmblood" breeds, such as the Trakehner or Hanoverian, developed when European carriage and war horseswere crossed with Arabians or Thoroughbreds, producing a riding horse with more refinement than a drafthorse, but greater size and milder temperament than a lighter breed.[106] Certain pony breeds with warmbloodcharacteristics have been developed for smaller riders.[107] Warmbloods are considered a "light horse" or"riding horse".[96]

Today, the term "Warmblood" refers to a specific subset of sport horse breeds that are used for competition indressage and show jumping.[108] Strictly speaking, the term "warm blood" refers to any cross between cold-blooded and hot-blooded breeds.[109] Examples include breeds such as the Irish Draught or the Cleveland Bay.The term was once used to refer to breeds of light riding horse other than Thoroughbreds or Arabians, such asthe Morgan horse.[98]

Sleep patterns

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

Horses are able to sleep both standing up and lying down. In anadaptation from life in the wild, horses are able to enter light sleep byusing a "stay apparatus" in their legs, allowing them to doze withoutcollapsing.[110] Horses sleep better when in groups because someanimals will sleep while others stand guard to watch for predators. Ahorse kept alone will not sleep well because its instincts are to keep aconstant eye out for danger.[111]

Unlike humans, horses do not sleep in a solid, unbroken period of time,but take many short periods of rest. Horses spend four to fifteen hours aday in standing rest, and from a few minutes to several hours lyingdown. Total sleep time in a 24-hour period may range from several

minutes to a couple of hours,[111] mostly in short intervals of about 15 minutes each.[112] The average sleeptime of a domestic horse is said to be 2.9 hours per day.[113]

Horses must lie down to reach REM sleep. They only have to lie down for an hour or two every few days tomeet their minimum REM sleep requirements.[111] However, if a horse is never allowed to lie down, afterseveral days it will become sleep-deprived, and in rare cases may suddenly collapse as it involuntarily slips intoREM sleep while still standing.[114] This condition differs from narcolepsy, although horses may also sufferfrom that disorder.[115]

Taxonomy and evolution

From left to right: Size development, biometrical changes inthe cranium, reduction of toes (left forefoot)

Main articles: Evolution of the horse, Equus (genus) and Equidae

The horse adapted to survive in areas of wide-openterrain with sparse vegetation, surviving in anecosystem where other large grazing animals,especially ruminants, could not.[116] Horses andother equids are odd-toed ungulates of the orderPerissodactyla, a group of mammals that wasdominant during the Tertiary period. In the past, thisorder contained 14 families, but only three—Equidae (the horse and related species), the tapir,and the rhinoceros—have survived to the presentday.[117]

The earliest known member of the Equidae familywas the Hyracotherium, which lived between 45and 55 million years ago, during the Eocene period.It had 4 toes on each front foot, and 3 toes on eachback foot.[118] The extra toe on the front feet soondisappeared with the Mesohippus, which lived 32 to37 million years ago.[119] Over time, the extra sidetoes shrank in size until they vanished. All that remains of them in modern horses is a set of small vestigialbones on the leg below the knee,[120] known informally as splint bones.[121] Their legs also lengthened as theirtoes disappeared until they were a hooved animal capable of running at great speed.[120] By about 5 millionyears ago, the modern Equus had evolved.[122] Equid teeth also evolved from browsing on soft, tropical plantsto adapt to browsing of drier plant material, then to grazing of tougher plains grasses. Thus proto-horseschanged from leaf-eating forest-dwellers to grass-eating inhabitants of semi-arid regions worldwide, includingthe steppes of Eurasia and the Great Plains of North America.

By about 15,000 years ago, Equus ferus was a widespread holarctic species. Horse bones from this time period,the late Pleistocene, are found in Europe, Eurasia, Beringia, and North America.[123] Yet between 10,000 and7,600 years ago, the horse became extinct in North America and rare elsewhere.[124][125][126] The reasons forthis extinction are not fully known, but one theory notes that extinction in North America paralleled humanarrival.[127] Another theory points to climate change, noting that approximately 12,500 years ago, the grassescharacteristic of a steppe ecosystem gave way to shrub tundra, which was covered with unpalatable plants.[128]

Wild species surviving into modern times

Main article: Wild horse

A truly wild horse is a species or subspecies with no ancestors that were ever domesticated. Therefore, most"wild" horses today are actually feral horses, animals that escaped or were turned loose from domestic herdsand the descendants of those animals.[129] Only two never-domesticated subspecies, the Tarpan and thePrzewalski's Horse, survived into recorded history and only the latter survives today.

A small herd of Przewalski's Horses

The Przewalski's horse (Equus ferus przewalskii), named after the Russian explorer Nikolai Przhevalsky, is arare Asian animal. It is also known as the Mongolian wild horse; Mongolian people know it as the taki, and theKyrgyz people call it a kirtag. The subspecies was presumed extinct in the wild between 1969 and 1992, while asmall breeding population survived in zoos around the world. In 1992, it was reestablished in the wild due to theconservation efforts of numerous zoos.[130] Today, a small wild breeding population exists inMongolia.[131][132] There are additional animals still maintained at zoos throughout the world.

The tarpan or European wild horse (Equus ferus ferus) was found inEurope and much of Asia. It survived into the historical era, but becameextinct in 1909, when the last captive died in a Russian zoo.[133] Thus,the genetic line was lost. Attempts have been made to recreate thetarpan,[133][134][135] which resulted in horses with outward physicalsimilarities, but nonetheless descended from domesticated ancestors andnot true wild horses.

Periodically, populations of horses in isolated areas are speculated to berelict populations of wild horses, but generally have been proven to beferal or domestic. For example, the Riwoche horse of Tibet wasproposed as such,[132] but testing did not reveal genetic differences from domesticated horses.[136] Similarly,the Sorraia of Portugal was proposed as a direct descendant of the Tarpan based on sharedcharacteristics,[137][138] but genetic studies have shown that the Sorraia is more closely related to other horsebreeds and that the outward similarity is an unreliable measure of relatedness.[137][139]

Other modern equids

Main article: Equus (genus)

Besides the horse, there are seven other species of genus Equus in the Equidae family. These are the ass ordonkey, Equus asinus; the mountain zebra, Equus zebra; plains zebra, Equus quagga; Grévy's zebra, Equusgrevyi; the kiang, Equus kiang; and the onager, Equus hemionus.[140]

Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a crossbetween a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny(female donkey).[141] Other hybrids include the zorse, a cross between a zebra and a horse.[142] With rareexceptions, most hybrids are sterile and cannot reproduce.[143]

DomesticationMain article: Domestication of the horse

Domestication of the horse most likely took place in central Asia prior to 3500 BC. Two major sources ofinformation are used to determine where and when the horse was first domesticated and how the domesticatedhorse spread around the world. The first source is based on palaeological and archaeological discoveries; thesecond source is a comparison of DNA obtained from modern horses to that from bones and teeth of ancienthorse remains.

Bhimbetka rock painting showingman riding on horse, India

The earliest archaeological evidence for the domestication of the horse comes from sites in Ukraine andKazakhstan, dating to approximately 3500–4000 BC.[144][145][146] By 3000 BC, the horse was completelydomesticated and by 2000 BC there was a sharp increase in the number of horse bones found in humansettlements in northwestern Europe, indicating the spread of domesticated horses throughout the continent.[147]

The most recent, but most irrefutable evidence of domestication comesfrom sites where horse remains were interred with chariots in graves ofthe Sintashta and Petrovka cultures c. 2100 BC.[148]

Domestication is also studied by using the genetic material of present-day horses and comparing it with the genetic material present in thebones and teeth of horse remains found in archaeological andpalaeological excavations. The variation in the genetic material showsthat very few wild stallions contributed to the domestic horse,[149][150]

while many mares were part of early domesticated herds.[139][151][152]

This is reflected in the difference in genetic variation between the DNAthat is passed on along the paternal, or sire line (Y-chromosome) versusthat passed on along the maternal, or dam line (mitochondrial DNA). There are very low levels of Y-chromosome variability,[149][150] but a great deal of genetic variation in mitochondrial DNA.[139][151][152]

There is also regional variation in mitochondrial DNA due to the inclusion of wild mares in domesticherds.[139][151][152][153] Another characteristic of domestication is an increase in coat color variation.[154] Inhorses, this increased dramatically between 5000 and 3000 BC.[155]

Before the availability of DNA techniques to resolve the questions related to the domestication of the horse,various hypotheses were proposed. One classification was based on body types and conformation, suggestingthe presence of four basic prototypes that had adapted to their environment prior to domestication.[105] Anotherhypothesis held that the four prototypes originated from a single wild species and that all different body typeswere entirely a result of selective breeding after domestication.[156] However, the lack of a detectablesubstructure in the horse has resulted in a rejection of both hypotheses.

Feral populations

Main article: Feral horse

Feral horses are born and live in the wild, but are descended from domesticated animals.[129] Many populationsof feral horses exist throughout the world.[157][158] Studies of feral herds have provided useful insights into thebehavior of prehistoric horses,[159] as well as greater understanding of the instincts and behaviors that drivehorses that live in domesticated conditions.[160]

There are also semi-feral horses in many parts of the world, such as Dartmoor and the New Forest in the UK,where the animals are all privately owned but live for significant amounts of time in "wild" conditions onundeveloped, often public, lands. Owners of such animals often pay a fee for grazing rights.[161][162]

Breeds

Equine hospital in the United Kingdom

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

The concept of purebred bloodstock and a controlled, written breed registry has come to be particularlysignificant and important in modern times. Sometimes purebred horses are incorrectly or inaccurately called"thoroughbreds". 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.[163] Horse breeds are groups of horses with distinctivecharacteristics that are transmitted consistently to their offspring, such as conformation, color, performanceability, or disposition. These inherited traits result from a combination of natural crosses and artificial selectionmethods. Horses have been selectively bred since their domestication. An early example of people whopracticed selective horse breeding were the Bedouin, who had a reputation for careful practices, keepingextensive pedigrees of their Arabian horses and placing great value upon pure bloodlines.[164] These pedigreeswere originally transmitted via an oral tradition.[165] In the 14th century, Carthusian monks of southern Spainkept meticulous pedigrees of bloodstock lineages still found today in the Andalusian horse.[166]

Breeds developed due to a need for "form to function", the necessity to develop certain characteristics in orderto perform a particular type of work.[167] Thus, a powerful but refined breed such as the Andalusian developedas riding horses with an aptitude for dressage.[167] Heavy draft horses developed out of a need to performdemanding farm work and pull heavy wagons.[168] Other horse breeds developed specifically for lightagricultural work, carriage and road work, various sport disciplines, or simply as pets.[169] Some breedsdeveloped through centuries of crossing other breeds, while others descended from a single foundation sire, orother limited or restricted foundation bloodstock. One of the earliest formal registries was General Stud Bookfor Thoroughbreds, which began in 1791 and traced back to the foundation bloodstock for the breed.[170] Thereare more than 300 horse breeds in the world today.[171]

Interaction with humansWorldwide, horses play a role within human cultures and have doneso for millennia. Horses are used for leisure activities, sports, andworking purposes. The Food and Agriculture Organization (FAO)estimates that in 2008, there were almost 59,000,000 horses in theworld, with around 33,500,000 in the Americas, 13,800,000 in Asiaand 6,300,000 in Europe and smaller portions in Africa andOceania. There are estimated to be 9,500,000 horses in the UnitedStates alone.[172] The American Horse Council estimates that horse-related activities have a direct impact on the economy of the UnitedStates of over $39 billion, and when indirect spending isconsidered, the impact is over $102 billion.[173] In a 2004 "poll"conducted by Animal Planet, more than 50,000 viewers from 73countries voted for the horse as the world's 4th favorite animal.[174]

Communication between human and horse is paramount in any equestrian activity;[175] to aid this processhorses are usually ridden with a saddle on their backs to assist the rider with balance and positioning, and abridle or related headgear to assist the rider in maintaining control.[176] Sometimes horses are ridden without a

A horse and rider in dressage competition atthe Olympics

saddle,[177] and occasionally, horses are trained to perform without a bridle or other headgear.[178] Many horsesare also driven, which requires a harness, bridle, and some type of vehicle.[179]

Sport

Main articles: Equestrianism, Horse racing, Horse trainingand Horse tack

Historically, equestrians honed their skills through games andraces. Equestrian sports provided entertainment for crowds andhoned the excellent horsemanship that was needed in battle. Manysports, such as dressage, eventing and show jumping, have originsin military training, which were focused on control and balance ofboth horse and rider. Other sports, such as rodeo, developed frompractical skills such as those needed on working ranches andstations. Sport hunting from horseback evolved from earlierpractical hunting techniques.[175] Horse racing of all typesevolved from impromptu competitions between riders or drivers.All forms of competition, requiring demanding and specializedskills from both horse and rider, resulted in the systematicdevelopment of specialized breeds and equipment for each sport. The popularity of equestrian sports throughthe centuries has resulted in the preservation of skills that would otherwise have disappeared after horsesstopped being used in combat.[175]

Horses are trained to be ridden or driven in a variety of sporting competitions. Examples include show jumping,dressage, three-day eventing, competitive driving, endurance riding, gymkhana, rodeos, and fox hunting.[180]

Horse shows, which have their origins in medieval European fairs, are held around the world. They host a hugerange of classes, covering all of the mounted and harness disciplines, as well as "In-hand" classes where thehorses are led, rather than ridden, to be evaluated on their conformation. The method of judging varies with thediscipline, but winning usually depends on style and ability of both horse and rider.[181] Sports such as polo donot judge the horse itself, but rather use the horse as a partner for human competitors as a necessary part of thegame. Although the horse requires specialized training to participate, the details of its performance are notjudged, only the result of the rider's actions—be it getting a ball through a goal or some other task.[182]

Examples of these sports of partnership between human and horse include jousting, in which the main goal isfor one rider to unseat the other,[183] and buzkashi, a team game played throughout Central Asia, the aim beingto capture a goat carcass while on horseback.[182]

Horse racing is an equestrian sport and major international industry, watched in almost every nation of theworld. There are three types: "flat" racing; steeplechasing, i.e. racing over jumps; and harness racing, wherehorses trot or pace while pulling a driver in a small, light cart known as a sulky.[184] A major part of horseracing's economic importance lies in the gambling associated with it.[185]

Work

A mounted police officer in Poland

Tanga (carriage) at Darbhanga Bihar

There are certain jobs that horses do very well, and no technology hasyet developed to fully replace them. For example, mounted police horsesare still effective for certain types of patrol duties and crowdcontrol.[186] Cattle ranches still require riders on horseback to round upcattle that are scattered across remote, rugged terrain.[187] Search andrescue organizations in some countries depend upon mounted teams tolocate people, particularly hikers and children, and to provide disasterrelief assistance.[188] Horses can also be used in areas where it isnecessary to avoid vehicular disruption to delicate soil, such as naturereserves. They may also be the only form of transport allowed inwilderness areas. Horses are quieter than motorized vehicles. Lawenforcement officers such as park rangers or game wardens may usehorses for patrols, and horses or mules may also be used for clearingtrails or other work in areas of rough terrain where vehicles are lesseffective.[189]

Although machinery has replaced horses in many parts of the world, anestimated 100 million horses, donkeys and mules are still used foragriculture and transportation in less developed areas. This numberincludes around 27 million working animals in Africa alone.[190] Someland management practices such as cultivating and logging can beefficiently performed with horses. In agriculture, less fossil fuel is usedand increased environmental conservation occurs over time with the useof draft animals such as horses.[191][192] Logging with horses can resultin reduced damage to soil structure and less damage to trees due to moreselective logging.[193]

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 withequipment that is authentic or a meticulously recreated replica, in various live action historical reenactments ofspecific periods of history, especially recreations of famous battles.[194] Horses are also used to preserve culturaltraditions and for ceremonial purposes. Countries such as the United Kingdom still use horse-drawn carriages toconvey royalty and other VIPs to and from certain culturally significant events.[195] Public exhibitions areanother example, such as the Budweiser Clydesdales, seen in parades and other public settings, a team of drafthorses that pull a beer wagon similar to that used before the invention of the modern motorized truck.[196]

Horses are frequently seen in television, films and literature. They are sometimes featured as a major characterin films about particular animals, but also used as visual elements that assure the accuracy of historicalstories.[197] Both live horses and iconic images of horses are used in advertising to promote a variety ofproducts.[198] The horse frequently appears in coats of arms in heraldry, in a variety of poses andequipment.[199] The mythologies of many cultures, including Greco-Roman, Hindu, Islamic, and Norse, include

The horse-headed deity in Hinduism,Hayagriva

Turkish cavalry, 1917

references to both normal horses and those with wings or additionallimbs, and multiple myths also call upon the horse to draw the chariotsof the Moon and Sun.[200] The horse also appears in the 12-year cycle ofanimals in the Chinese zodiac related to the Chinese calendar.[201]

Therapeutic use

See also: Hippotherapy and Therapeutic horseback riding

People of all ages with physical and mental disabilities obtain beneficialresults from association with horses. Therapeutic riding is used tomentally and physically stimulate disabled persons and help themimprove their lives through improved balance and coordination,increased self-confidence, and a greater feeling of freedom andindependence.[202] The benefits of equestrian activity for people withdisabilities has also been recognized with the addition of equestrianevents to the Paralympic Games and recognition of para-equestrianevents by the International Federation for Equestrian Sports (FEI).[203]

Hippotherapy and therapeutic horseback riding are names for differentphysical, occupational, and speech therapy treatment strategies that utilize equine movement. In hippotherapy, atherapist uses the horse's movement to improve their patient's cognitive, coordination, balance, and fine motorskills, whereas therapeutic horseback riding uses specific riding skills.[204]

Horses also provide psychological benefits to people whether they actually ride or not. "Equine-assisted" or"equine-facilitated" therapy is a form of experiential psychotherapy that uses horses as companion animals toassist people with mental illness, including anxiety disorders, psychotic disorders, mood disorders, behavioraldifficulties, and those who are going through major life changes.[205] There are also experimental programsusing horses in prison settings. Exposure to horses appears to improve the behavior of inmates and help reducerecidivism when they leave.[206]

Warfare

Main article: Horses in warfare

Horses have been used in warfare for most of recorded history. The firstarchaeological evidence of horses used in warfare dates to between 4000to 3000 BC,[207] and the use of horses in warfare was widespread by theend of the Bronze Age.[208][209] Although mechanization has largelyreplaced the horse as a weapon of war, horses are still seen today inlimited military uses, mostly for ceremonial purposes, or forreconnaissance and transport activities in areas of rough terrain wheremotorized vehicles are ineffective. Horses have been used in the 21stcentury by the Janjaweed militias in the War in Darfur.[210]

Products

Checking teeth and other physicalexaminations are an important part ofhorse care.

Horses are raw material for many products made by humans throughout history, including byproducts from theslaughter 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 theMongols, who let it ferment to produce kumis.[211] Horse blood was once used as food by the Mongols andother 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.[211] The drug Premarinis a mixture of estrogens extracted from the urine of pregnant mares (pregnant mares' urine), and waspreviously a widely used drug for hormone replacement therapy.[212] The tail hair of horses can be used formaking bows for string instruments such as the violin, viola, cello, and double bass.[213]

Horse meat has been used as food for humans and carnivorous animals throughout the ages. It is eaten in manyparts of the world, though consumption is taboo in some cultures,[214] and a subject of political controversy inothers.[215] Horsehide leather has been used for boots, gloves, jackets,[216] baseballs,[217] and baseball gloves.Horse hooves can also be used to produce animal glue.[218] Horse bones can be used to make implements.[219]

Specifically, in Italian cuisine, the horse tibia is sharpened into a probe called a spinto, which is used to test thereadiness of a (pig) ham as it cures.[220] In Asia, the saba is a horsehide vessel used in the production ofkumis.[221]

Care

Main article: Horse careSee also: Equine nutrition, Horse grooming, Veterinary medicine and Farrier

Horses are grazing animals, and their major source of nutrients is good-quality forage from hay or pasture.[222] They can consumeapproximately 2% to 2.5% of their body weight in dry feed each day.Therefore, a 450-kilogram (990 lb) adult horse could eat up to 11kilograms (24 lb) of food.[223] Sometimes, concentrated feed such asgrain is fed in addition to pasture or hay, especially when the animal isvery active.[224] When grain is fed, equine nutritionists recommend that50% or more of the animal's diet by weight should still be forage.[225]

Horses require a plentiful supply of clean water, a minimum of 10 USgallons (38 L) to 12 US gallons (45 L) per day.[226] Although horses are

adapted to live outside, they require shelter from the wind and precipitation, which can range from a simpleshed or shelter to an elaborate stable.[227]

Horses require routine hoof care from a farrier, as well as vaccinations to protect against various diseases, anddental examinations from a veterinarian or a specialized equine dentist.[228] If horses are kept inside in a barn,they require regular daily exercise for their physical health and mental well-being.[229] When turned outside,they require well-maintained, sturdy fences to be safely contained.[230] Regular grooming is also helpful to helpthe horse maintain good health of the hair coat and underlying skin.[231]

See alsoGlossary of equestrian terms

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Further readingApperson, George Latimer and Martin Manser (2006). Dictionary of Proverbs. Wordsworth Editions. ISBN 1-84022-311-1.

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Chamberlin, J. Edward (2006). Horse: How the Horse Has Shaped Civilizations. New York, NY: Bluebridge. ISBN 0-9742405-9-1. OCLC 61704732.Hammond, Gerald (2000). The Language of Horse Racing. London: Taylor & Francis. ISBN 1-57958-276-1.OCLC 44923115.

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