| Yak | |
|---|---|
 | |
| A yak nearChagan-Uzun, Altai Republic, Russia | |
Domesticated | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Artiodactyla |
| Family: | Bovidae |
| Subfamily: | Bovinae |
| Genus: | Bos |
| Species: | B. grunniens |
| Binomial name | |
| Bos grunniens Linnaeus, 1766 | |
| Synonyms | |
Poephagus grunniens | |
Theyak (Bos grunniens), also known as theTartary ox,grunting ox,[1]hairy cattle,[2]sarlak orsarlyk,[3] ordomestic yak, is a species of long-haireddomesticatedcattle found throughout theHimalayan region, theTibetan Plateau,Tajikistan, thePamir Mountains, and as far north asMongolia andSiberia. It is descended from thewild yak (Bos mutus).[4]
The English wordyak originates from theTibetan:གཡག་,Wylie:g.yag. In Tibetan andBalti it refers only to the male of the species, the female being calledTibetan:འབྲི་,Wylie: 'bri orTibetan:གནག,Wylie:gnag in Tibetan andTibetan:ཧཡག་མོ་,Wylie:hYag-mo in Balti. In English, as in most other languages that have borrowed the word,yak is usually used for both sexes, withbull orcow referring to each sex separately.
Belonging to the genusBos, yaks are related tocattle andbison.Mitochondrial DNA analyses to determine the evolutionary history of yaks have been inconclusive.
The yak may have diverged from cattle at any point between one and five million years ago, and there is some suggestion that it may be more closely related to bison than to the other members of its designated genus.[5] Apparent close fossil relatives of the yak, such asBos baikalensis, have been found in eastern Russia, suggesting a possible route by which yak-like ancestors of the modernAmerican bison could have entered the Americas.[6]
The species was originally designated asBos grunniens ("grunting ox") byLinnaeus in 1766. Still, this name is now generally considered to refer only to the domesticated form of the animal, withBos mutus ("mute ox") being the preferred name for the wild species. Although some authors still consider the wild yak to be asubspecies,Bos grunniens mutus, theICZN madean official ruling in 2003[7] permitting the use of the nameBos mutus forwild yaks, and this is now the more common usage.[8][6][9]
There are no recognised subspecies of yak except where the wild yak is considered a subspecies ofBos grunniens.
Yaks are heavily built animals with bulky frames, sturdy legs, rounded, cloven hooves, and extremely dense, long fur hanging lower than the belly. While wild yaks are generally dark, blackish to brown in colouration, domestic yaks can be quite variable, often having rusty brown and cream patches. They have small ears and broad foreheads, with smooth horns that are generally dark in colour. In males (bulls), the horns sweep out from the sides of the head and then curve backwards; they typically range from 48 to 99 cm (19 to 39 in) in length.
The horns of females (cows) are smaller, at 27 to 64 cm (11 to 25 in) in length, and have a more upright shape. Both sexes have a short neck with a pronounced hump over the shoulders, although this is larger and more visible in males.[6] Males weigh 350 to 585 kg (772 to 1,290 lb), females weigh 225 to 255 kg (496 to 562 lb). Wild (feral) yaks can be substantially heavier, bulls reaching weights of up to 1,000 kg (2,200 lb).[10] Depending on the breed, domestic yak males are 111–138 cm (44–54 in) high at the withers, while females are 105–117 cm (41–46 in) high at the withers.[11]
Both sexes have long, shaggy hair with a dense woolly undercoat over the chest, flanks, and thighs to insulate them from the cold. Especially in bulls, this may form a long "skirt" that can reach the ground. The tail is long and horselike rather than tufted like the tails of cattle or bison. Domesticated yaks have a wide range of coat colours, with some individuals being white, grey, brown,roan orpiebald. Theudder in females and thescrotum in males are small and hairy as protection against the cold. Females have fourteats.[6]
Yaks are not known to produce the characteristic lowing (mooing) sound of cattle, but both wild and domestic yaks grunt and squeak, which inspired the scientific name of the domestic yak variant,Bos grunniens (grunting bull).Nikolay Przhevalsky named the wild variantBos mutus (silent bull), believing that it did not make a sound at all, but it does.[12]
Yak physiology is welladapted to high altitudes, having larger lungs and heart than cattle found at lower altitudes, as well as greater capacity for transporting oxygen through their blood,[13][14] due to the persistence offoetal haemoglobin throughout life.[15] Conversely, yaks have trouble thriving at lower altitudes,[16] and are prone to suffering from heat exhaustion above about 15 °C (59 °F). Further adaptations to the cold include a thick layer ofsubcutaneous fat and an almost complete lack of functionalsweat glands.[13]
Compared with domestic cattle, therumen of yaks is unusually large, relative to theomasum.[citation needed] This likely allows them to consume greater quantities of low-quality food at a time, and to ferment it longer to extract more nutrients.[13] Yak consume the equivalent of 1% of their body weight daily while cattle require 3% to maintain condition.[citation needed] They are grazing herbivores, with their wild ancestors feeding primarily ongrass andsedges,[17] with some herbs and dwarf shrubs.[18]
Yaks mate in the summer, typically between July and September, depending on the local environment. For the remainder of the year, many bulls wander in small bachelor groups away from the large herds. Still, as therut approaches, they become aggressive and regularly fight with each other to establish dominance. In addition to non-violent threat displays, bellowing, and scraping the ground with their horns, bull yaks compete more directly, repeatedly charging at each other with heads lowered or sparring with their horns. Likebison, but unlike cattle, males wallow in dry soil during the rut, often whilescent-marking with urine or dung.[6] Females enteroestrus up to four times a year, and females are receptive only for a few hours in each cycle.[19]
Gestation lasts between 257 and 270 days,[13] so that the young are born between May and June, and results in the birth of a single calf. The cow finds a secluded spot to give birth, but the calf can walk within about ten minutes of birth, and the pair soon rejoin the herd.[13] Females of both the wild and domestic forms typically give birth only once every other year,[6] although more frequent births are possible if the food supply is good.
Calves areweaned at one year and become independent shortly thereafter. Wild calves are initially brown in color and only later develop darker adult hair. Females generally give birth for the first time at three or four years of age,[20] and reach their peak reproductive fitness at around six years. Yaks may live for more than twenty years in domestication or captivity,[6] although it is likely that this may be somewhat shorter in the wild.
For thousands of years,[citation needed] domesticated yaks have been kept in Mongolia and Tibet, primarily for their milk,fibre (wool), and meat, and asbeasts of burden.[21] Their dried droppings are an important fuel, used all over Tibet, and are often the only fuel available on the high, treelessTibetan Plateau. Yaks transport goods across mountain passes for local farmers and traders and are an attraction for climbing and trekking expeditions: "Only one thing makes it hard to use yaks for long journeys in barren regions. They will not eatgrain, which could be carried on the journey. They will starve unless they can be brought to a place where there is grass."[22] They also are used to drawploughs.[23] Yaks' milk is often processed to a cheese calledchhurpi in Tibetan and Nepali languages, andbyaslag in Mongolia.Butter made from yaks' milk is an ingredient of thebutter tea that Tibetans consume in large quantities,[24] and is also used in lamps and made intobutter sculptures used in religious festivities.[25]
Small numbers of herds can be found in the United States, Canada, New Zealand, and some parts of Europe. Yaks have generated interest outside the Himalayas as a commercial crop and by cattle breeders. The main interest of North American yak breeders is lean meat production byhybridizing with other cattle, followed bywool production.[26]
TheIndian government established a dedicated centre for research into yak husbandry, the ICAR-National Research Centre on Yak, in 1989. It is located atDirang, Arunachal Pradesh, and maintains a yak farm in the Nyukmadung area at an altitude of 2,750 metres (9,020 ft) above MSL.[27]
InNepal,Tibet, andMongolia, domestic cattle are crossbred with yaks. This gives rise to the infertile maledzo མཛོ། as well as fertile females known asdzomo orzhom མཛོ་མོ།, which may be crossed again with cattle. The Dwarf Lulu breed, "the onlyBos primigenius taurus type of cattle in Nepal" has been tested for DNA markers and found to be a mixture of both taurine andzebu types of cattle (B. p. taurus andB. p. indicus) with yak.[28] According to theInternational Veterinary Information Service, the low productivity of second-generation cattle–yak crosses makes them suitable only as meat animals.[29]
Crosses between yaks and domestic cattle (Bos primigenius taurus) have been recorded in Chinese literature for at least 2,000 years.[6] Successful crosses have also been recorded betweenyak and American bison,[29]gaur, andbanteng, generally with similar results to those produced with domestic cattle.[6]
Jacques et al. (2021)[30] show that most elaborate yak-related terminologies are found within Tibetic andGyalrongic languages. Both branches also have native terms foryak-cattle hybrids, suggesting that Tibetic and Gyalrongic speakers may have independently cross-bred yaks and cattle, predating the proto-Gyalrongic split (3221 [2169–4319]BP[31]) from Tibeto-Gyalrongic. The oldest dated physical evidence of yak domestication is from 2,500 years BP.[32]
In parts of Tibet and Karakorum,yak racing is a form of entertainment at traditional festivals and an important part of their culture. More recently, sports involving domesticated yaks, such asyak skiing oryak polo, are being marketed as tourist attractions in South Asian countries, including inGilgit-Baltistan, Pakistan.[citation needed]
In Nepal, an annual festival is held to drink the fresh blood of yak, and it is believed that it cures various diseases such as gastritis,jaundice, and body strain.[33][34] The fresh blood is extracted from the neck of a yak without killing it. The cut is healed after the ceremony is over.[35] The ritual is believed to be originated in Tibet andMustang.[36]
Traditionally, yaks are used to transport deceased people tocharnel grounds forsky burials in Tibet, with Tibetan practice holding that the yaks be set free upon the conclusion of the task.[37][38][39][40]
Yak skiing is a sport practiced in the Indian hill resort ofManali, Himachal Pradesh, as a tourist attraction. The sport involves a skier waiting at the bottom of a slope and ayak at the top of the hill; yak and skier are connected by means of a rope going around apulley at the top of the hill. To engage the yak, the skier must shake (and swiftly put down) a bucket ofpony nuts. This attracts the yak, which charges downhill and pulls the skier upward by means of the rope.[41][42]
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