Horses must lie down to reach REM sleep

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.^[104] 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.^[107] HP Compaq HSTNN-XB62 Battery This condition differs from narcolepsy, although horses may also suffer from that disorder. The horse adapted to survive in areas of wide-open terrain with sparse vegetation, surviving in anecosystem where other large grazing animals, especially ruminants, could not.^[109] Horses and other equids are odd-toed ungulates of the order Perissodactyla, a group of mammals that was dominant during theTertiary period. HP Compaq HSTNN-XB68 Battery In the past, this order contained 14 families, but only three—Equidae (the horse and related species), the tapir, and the rhinoceros—have survived to the present day.^[110] The earliest known member of the Equidae family was the Hyracotherium, which lived between 45 and 55 million years ago, during the Eocene period. It had 4 toes on each front foot, and 3 toes on each back foot.^[111] HP Compaq HSTNN-XB69 Battery The extra toe on the front feet soon disappeared with the Mesohippus, which lived 32 to 37 million years ago.^[112] Over time, the extra side toes shrank in size until they vanished. All that remains of them in modern horses is a set of small vestigial bones on the leg below the knee,^[113] known informally as splint bones.^[114] HP Compaq HSTNN-XB85 Battery Their legs also lengthened as their toes disappeared until they were a hooved animal capable of running at great speed.^[113] By about 5 million years ago, the modern Equus had evolved.^[115] Equid teeth also evolved from browsing on soft, tropical plants to adapt to browsing of drier plant material, then to grazing of tougher plains grasses. HP 448007-001 battery Thus 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. 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, BeringiaHP Pavilion DV7 battery , and North America.^[116] Yet between 10,000 and 7,600 years ago, the horse became extinct in North America and rare elsewhere.^{[117][118][119]} The reasons for this extinction are not fully known, but one theory notes that extinction in North America paralleled human arrival.^[120] Another theory points to climate change, HP DV6-1120SA battery noting that approximately 12,500 years ago, the grasses characteristic of a steppe ecosystem gave way to shrub tundra, which was covered with unpalatable plants. 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, HP DV6-1210SA battery animals that escaped or were turned loose from domestic herds and the descendants of those animals.^[122] Only two never-domesticated subspecies, the Tarpan and the Przewalski's Horse, survived into recorded history and only the latter survives today. The Przewalski's Horse (Equus ferus przewalskii), named after the Russian explorer Nikolai Przhevalsky, is a rare Asian animal. Compaq CQ50 battery It is also known as the Mongolian Wild Horse; Mongolian people know it as the taki, and the Kyrgyz people call it akirtag. The subspecies was presumed extinct in the wild between 1969 and 1992, while a small breeding population survived in zoos around the world. In 1992, it was reestablished in the wild due to the conservation efforts of numerous zoos. HP Pavilion DV8 battery Today, a small wild breeding population exists in Mongolia. There are additional animals still maintained at zoos throughout the world. The Tarpan or European Wild Horse (Equus ferus ferus) was found in Europe and much of Asia. It survived into the historical era, but became extinct in 1909, when the last captive died in a Russian zoo. Sony VGP-BPS13 battery Thus, the genetic line was lost. Attempts have been made to recreate the Tarpan,which resulted in horses with outward physical similarities, but nonetheless descended from domesticated ancestors and not true wild horses. Periodically, populations of horses in isolated areas are speculated to be relict populations of wild horses, but generally have been proven to be feral or domestic. HP DV9700 battery For example, the Riwoche horse of Tibet was proposed as such,but testing did not reveal genetic differences with domesticated horses.^[129]Similarly, the Sorraia of Portugal was proposed as a direct descendant of the Tarpan based on shared characteristics, but genetic studies have shown that the Sorraia is more closely related to other horse breeds and that the outward similarity is an unreliable measure of relatedness. Compaq CQ35-100 battery Besides the horse, there are seven other species of genus Equus in the Equidae family. These are the ass or donkey, Equus asinus; the mountain zebra, Equus zebra; plains zebra, Equus quagga; Grévy's zebra, Equus grevyi; the kiang, Equus kiang; and the onager, Equus hemionus.^[133] Sony VGP-BPS11 battery Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey).^[134] Other hybrids include the zorse, a cross between a zebra and a horse.^[135] With rare exceptions, most hybrids are sterile and cannot reproduce. HP Probook 4210S Battery Domestication of the horse most likely took place in central Asia prior to 3500 BC. Two major sources of information are used to determine where and when the horse was first domesticated and how the domesticated horse spread around the world. The first source is based on palaeological and archaeological discoveries, HP Probook 4310S Battery the second source is a comparison of DNA obtained from modern horses to that from bones and teeth of ancient horse remains. The earliest archaeological evidence for the domestication of the horse comes from sites in Ukraine and Kazakhstan, dating to approximately 3500–4000 BC.By 3000 BC, HP Probook 4311S Battery the horse was completely domesticated and by 2000 BC there was a sharp increase in the number of horse bones found in human settlements in northwestern Europe, indicating the spread of domesticated horses throughout the continent.The most recent, but most irrefutable evidence of domestication comes from sites where horse remains were interred with chariots in graves of the Sintashta and Petrovka cultures c. 2100 BC. HP Probook 4410S Battery Domestication is also studied by using the genetic material of present day horses and comparing it with the genetic material present in the bones and teeth of horse remains found in archaeological and palaeological excavations. The variation in the genetic material shows that very few wild stallions contributed to the domestic horse, HP Probook 4411S Battery while many mares were part of early domesticated herds.This is reflected in the difference in genetic variation between the DNA that is passed on along the paternal, or sire line (Y-chromosome) versus that passed on along the maternal, or dam line (mitochondrial DNA). HP Probook 4415S Battery There are very low levels of Y-chromosome variability,but a great deal of genetic variation in mitochondrial DNA.There is also regional variation in mitochondrial DNA due to the inclusion of wild mares in domestic herds.Another characteristic of domestication is an increase in coat color variation.In horses, this increased dramatically between 5000 and 3000 BC. HP Probook 4416S Battery Before the availability of DNA techniques to resolve the questions related to the domestication of the horse, various hypothesis were proposed. One classification was based on body types and conformation, suggesting the presence of four basic prototypes that had adapted to their environment prior to domestication. HP Probook 4510S Battery Another hypothesis held that the four prototypes originated from a single wild species and that all different body types were entirely a result of selective breeding after domestication.^[148] However, the lack of a detectable substructure in the horse has resulted in a rejection of both hypotheses. HP Probook 4510S/CT Battery Feral horses are born and live in the wild, but are descended from domesticated animals.^[122] Many populations of feral horses exist throughout the world.^[  Studies of feral herds have provided useful insights into the behavior of prehistoric horses,^[151] as well as greater understanding of the instincts and behaviors that drive horses that live in domesticated conditions.^[152] HP Probook 4515S Battery 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 owne The concept of purebred bloodstock and a controlled, written breed registry has come to be particularly significant and important in modern times. HP Probook 4515S/CT Battery 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.^[155] Horse breeds are groups of horses with distinctive characteristics that are transmitted consistently to their offspring, such as conformation, color, performance ability, or disposition. HP Probook 4710S Battery These inherited traits result from a combination of natural crosses and artificial selection methods. Horses have been selectively bred since their domestication. An early example of people who practiced selective horse breeding were the Bedouin, who had a reputation for careful practices, keeping extensive pedigrees of their Arabian horses and placing great value upon pure bloodlines.^[156] HP Probook 4710S/CT Battery These pedigrees were originally transmitted via an oral tradition.^[157] In the 14th century, Carthusian monks of southern Spain kept meticulous pedigrees of bloodstock lineages still found today in the Andalusian horse.^[158] Breeds developed due to a need for "form to function", the necessity to develop certain characteristics in order to perform a particular type of work.^[159] HP Probook 6440B Battery Thus, a powerful but refined breed such as the Andalusian developed as riding horses with an aptitude for dressage.^[159] Heavy draft horses developed out of a need to perform demanding farm work and pull heavy wagons.^[160] Other horse breeds developed specifically for light agricultural work, carriage and road work, various sport disciplines, or simply as pets. HP Probook 6445B Battery Some breeds developed through centuries of crossing other breeds, while others descended from a single foundation sire, or other limited or restricted foundation bloodstock. One of the earliest formal registries was General Stud Book for Thoroughbreds, which began in 1791 and traced back to the foundation bloodstock for the breed.^[162] HP Probook 6540B Battery There are more than 300 horse breeds in the world today. Worldwide, horses play a role within human cultures and have done so for millennia. Horses are used for leisure activities, sports, and working purposes. TheFood and Agriculture Organization (FAO) estimates that in 2008, there were almost 59,000,000 horses in the world, HP Probook 6545B Battery with around 33,500,000 in the Americas, 13,800,000 in Asia and 6,300,000 in Europe and smaller portions in Africa and Oceania. There are estimated to be 9,500,000 horses in the United States alone.^[164] The American Horse Council estimates that horse-related activities have a direct impact on the economy of the United States of over $39 billion, HP 500014-001 Battery and when indirect spending is considered, the impact is over $102 billion.^[165] 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.^[166] Communication between human and horse is paramount in any equestrian activity; HP 500028-142 Battery to aid this process horses are usually ridden with a saddle on their backs to assist the rider with balance and positioning, and a bridle or related headgear to assist the rider in maintaining control.^[168] Sometimes horses are ridden without a saddle,^[169] and occasionally, horses are trained to perform without a bridle or other headgear.^[170] HP 500029-141 Battery Many horses are also driven, which requires aharness, bridle, and some type of vehicle. Historically, equestrians honed their skills through games and races. Equestrian sports provided entertainment for crowds and honed the excellent horsemanship that was needed in battle. HP 500029-142 Battery Many sports, such as dressage, eventing and show jumping, have origins in military training, which were focused on control and balance of both horse and rider. Other sports, such as rodeo, developed from practical skills such as those needed on working ranches and stations. Sport hunting from horseback evolved from earlier practical hunting techniques.^[167] HP 500765-001 Battery Horse racing of all types evolved from impromptu competitions between riders or drivers. All forms of competition, requiring demanding and specialized skills from both horse and rider, resulted in the systematic development of specialized breeds and equipment for each sport. HP 501114-001 Battery The popularity of equestrian sports through the centuries has resulted in the preservation of skills that would otherwise have disappeared after horses stopped being used in combat.^[172] Horses are trained to be ridden or driven in a variety of sporting competitions. Examples include show jumping,dressage, three-day eventing, competitive driving, HP 506066-721 Battery endurance riding, gymkhana, rodeos, and fox hunting.^[173] Horse shows, which have their origins in medieval European fairs, are held around the world. They host a huge range of classes, covering all of the mounted and harness disciplines, as well as "In-hand" classes where the horses are led, rather than ridden, to be evaluated on their conformation. HP 513127-251 Battery The method of judging varies with the discipline, but winning usually depends on style and ability of both horse and rider.^[174] 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 requires specialized training to participate, HP 513128-251 Battery 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 task.^[175] Examples of these sports of partnership between human and horse include jousting, in which the main goal is for one rider to unseat the other,^[176HP 513128-361 Battery ^] and buzkashi, a team game played throughout Central Asia, the aim being to capture a goat carcass while on horseback.^[175] Horse racing is an equestrian sport and major international industry, watched in almost every nation of the world. There are three types: "flat" racing;steeplechasing, i.e. racing over jumps; HP 513130-321 Battery and harness racing, where horses trot or pace while pulling a driver in a small, light cart known as a sulky.^[177] A major part of horse racing's economic importance lies in the gambling associated with it. There are certain jobs that horses do very well, and no technology has yet developed to fully replace them. HP 516479-121 Battery For example, mounted police horses are still effective for certain types of patrol duties and crowd control.^[179] Cattleranches still require riders on horseback to round up cattle that are scattered across remote, rugged terrain.^[180]Search and rescue organizations in some countries depend upon mounted teams to locate people, particularly hikers and children, HP 530801-001 Battery and to provide disaster relief assistance.^[181] Horses can also be used in areas where it is necessary to avoid vehicular disruption to delicate soil, such as nature reserves. They may also be the only form of transport allowed in wilderness areas. Horses are quieter than motorized vehicles. HP 530802-001 Battery Law enforcement officers such as park rangersor 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. Although machinery has replaced horses in many parts of the world, an estimated 100 million horses, HP 532492-11 Battery donkeys and mules are still used for agriculture and transportation in less developed areas. This number includes around 27 millionworking animals in Africa alone.Some land management practices such as cultivating and logging can be efficiently performed with horses. In agriculture, HP 532496-541 Battery less fossil fuel is used and increased environmental conservation occurs over time with the use of draft animals such as horses.Logging with horses can result in reduced damage to soil structure and less damage to trees due to more selective logging. Modern horses are often used to reenact many of their historical work purposes. HP 535806-001 Battery Horses are used, complete with equipment that is authentic or a meticulously recreated replica, in various live action historical reenactments of specific periods of history, especially recreations of famous battles.^[187] Horses are also used to preserve cultural traditions and for ceremonial purposes. HP 535808-001 Battery Countries such as the United Kingdom still use horse-drawn carriages to convey royalty and other VIPs to and from certain culturally significant events.^[188] Public exhibitions are another example, such as the Budweiser Clydesdales, seen in parades and other public settings, a team of draft horses that pull a beer wagon similar to that used before the invention of the modern motorized truck.^[189] HP 538692-351 Battery Horses are frequently seen in television and films. They are sometimes featured as a major character in films about particular animals, but also used as visual elements that assure the accuracy of historical stories.^[190] Both live horses and iconic images of horses are used in advertising to promote a variety of products.^[191] HP 538692-541 Battery The horse frequently appears in coats of arms in heraldry, in a variety of poses and equipment.^[192] The mythologies of many cultures, includingGreco-Roman, Hindu, Islamic, and Norse, include references to both normal horses and those with wings or additional limbs, and multiple myths also call upon the horse to draw the chariots of the Moon and Sun.^[193] HP 572831-121 Battery The horse also appears in the 12-year cycle of animals in the Chinese zodiac related to the Chinese calendar. People of all ages with physical and mental disabilities obtain beneficial results from association with horses. HP 572831-541 Battery 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.^[195] HP 577093-001 Battery 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 International Federation for Equestrian Sports (FEI).^[196]Hippotherapy and therapeutic horseback riding are names for different physical, occupational, HP 579027-001 Battery and speech therapy treatment strategies that utilize equine movement. In hippotherapy, a therapist uses the horse's movement to improve their patient's cognitive, coordination, balance, and fine motor skills, whereas therapeutic horseback riding uses specific riding skills.^[197] HP 580029-001 Battery 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 to assist people with mental illness, including anxiety disorders, psychotic disorders, mood disorders, behavioral difficulties, HP 586006-321 Battery and those who are going through major life changes.^[198] There are also experimental programs using horses in prisonsettings. Exposure to horses appears to improve the behavior of inmates and help reduce recidivism when they leave. Horses in warfare have been seen for most of recorded history. The first archaeological evidence of horses used in warfare dates to between 4000 to 3000 BC,^[200] HP 586006-361 Battery and the use of horses in warfare was widespread by the end of the Bronze Age.Although mechanization has largely replaced the horse as a weapon of war, horses are still seen today in limited military uses, mostly for ceremonial purposes, or for reconnaissance and transport activities in areas of rough terrain where motorized vehicles are ineffective. HP 586028-341 Battery Horses have been used in the 21st century by the Janjaweed militias in the War in Darfur. Horses are 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. HP 588178-141 Battery 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.^[204] Horse blood was once used as food by the Mongols and other nomadic tribes, who found it a convenient source of nutrition when traveling. HP 593553-001 Battery