Bos grunniens

The yak is a large, long-haired wild ox of the Tibetan Plateau and the Himalaya, built for cold, thin air at 3,000–5,500 m. The wild yak (Bos mutus) is a Vulnerable species with roughly 15,000–20,000 left. About 16 million domestic yaks (Bos grunniens), tamed from wild yaks around 7,300 years ago, give herders milk, butter, wool, transport and dung for fuel.

Also known as Dri (Tibetan for a female yak), Yag (Tibetan for a yak bull), “Boat of the plateau” (nickname for pack yaks)

Yak abilities

≈2× lung weight of local cattle
High on the plateau, every breath carries far less oxygen. Big lungs, a big heart and relaxed lung blood vessels let yaks cope.
- Air at 3,500 m has about 35% less oxygen than at sea level, and at 5,000 m about half.
- Yak lungs weighed 3.7 kg in one study, about twice the 1.8 kg of local cattle.
- In cows taken high up, the lung blood vessels clamp down and blood pressure in the lungs rises dangerously. In yaks this reaction has almost disappeared.
- Yak haemoglobin, the oxygen carrier in blood, holds on to oxygen more tightly than cow haemoglobin. The yak genome shows many genes linked to low oxygen.
Lung weight
Yak3.7 kg
Yak × cattle hybrid2.5 kg
Local cattle1.8 kg
Zhongdian, Yunnan, China: 12 yaks, 10 hybrids, 5 cattle.
Sources [2, 7, 8, 10, 11]
−40 °C still grazing normally
Three layers of hair, thick skin and almost no sweating keep the heat in. Yaks feed and move normally at −30 to −40 °C.
- Thick outer hairs (70–90 µm across) sit over a soft winter down only 16–20 µm thin.
- No case of frostbite has been recorded in yaks, even on their ears or tails.
- In the cold season a yak’s heart beats about 51 times a minute, against 78 in the warm season, and its body runs on less energy.
- The flip side: yaks struggle in heat. Above 13 °C they breathe faster, and at about 20 °C they stop grazing.
How thick is each hair?
Coarse outer hair70–90 µm
Winter down16–20 µm
A micrometre (µm) is a thousandth of a millimetre.
Sources [2, 12]
May–June when the winter wool comes off
Each autumn a yak grows a thick winter coat. In early summer the woolly down loosens and falls out in clumps.
- Hair and down grow before winter and are shed in late spring or early summer if nobody harvests them.
- Herders shear their yaks or comb out the soft down once a year, in May–June. Combing gets more down.
- Since the 1970s, the textile industry has spun yak down into soft yarn for clothes.
Sources [3, 5, 12]
>20× more likely near snow (females vs males)
In winter, when streams freeze solid, wild yaks are thought to eat snow for water.
- Early travellers on the plateau already reported wild yaks eating snow.
- In winter surveys in Hoh Xil (Kekexili), Tibet, female wild yaks were more than 20 times as likely as males to be found within 200 m of snow patches.
- With streams and lakes frozen, snow may be their main water. Females and young live in big herds, about 30 on average; bulls roam in twos and threes.
Sources [1, 13]
28–38 kg grass eaten in 10 hours in summer
When snow and ice cover the pasture, yaks break through with their hooves and heads to reach the old grass beneath.
- Herders even send yaks ahead to stamp tracks through deep snow for people, a sort of “biological snow plough”.
- In winter there is so little grass that a yak may eat 13 kg or less in 10 hours, against 28–38 kg in summer.
- Over a long winter yaks can lose 25–30% of their body weight, then put it back on in summer.
Grass eaten in 10 hours
Summer28–38 kg
Winter≤13 kg
Sources [2, 12]
grunniens Latin for “grunting”
Yaks do not moo. They grunt, which gave the domestic yak its scientific name, Bos grunniens: the grunting ox.
- The wild yak was named Bos mutus, “mute ox”, by a Russian explorer who thought it was silent. Scientists call that a poor name: wild yaks are quite noisy.
- In the breeding season wild yaks grunt, bellow, squeak and cry.
- A threatened wild herd may snort loudly before running off or charging.
Sources [1, 6, 14, 15]
100+ herd size that rarely loses animals to predators
Faced with wolves, a herd bunches into a tight group with the calves in the middle and the horns facing out.
- Herds of 100 or more yaks rarely lose animals to predators. Bulls have reportedly killed wolves with their horns.
- Wolves and brown bears are the main wild predators. Snow leopards take domestic yaks in some areas.
- In the breeding season, rival bulls stand side-on 3–6 m apart to show off their size, and may then spar for up to 15 minutes.
Sources [1, 2, 16]
60–80 kg load, 20–30 km a day
Domestic yaks are the “boat of the plateau”: steady pack animals that carry loads over high passes and snowy ground.
- A normal pack load is 60–80 kg, carried 20–30 km a day. One test team of steers carried 75 kg for 30 km in 6.2 hours, about 4.8 km/h.
- The heaviest load on record is 300 kg, at 4,100 m in Qinghai: 82% of that yak’s own weight.
- Pack steers can cross terrain as high as 7,200 m and can work for 2–3 days without food or water.
Pack loads
Record load300 kg
Normal load60–80 kg
Sources [2, 17]

Tap a pin on the model or a part below.

up to 99 cm a wild bull’s horn, along the curve
- Both bulls and cows grow horns. They sweep out sideways, then curve upwards.
- Measured along the outside curve, wild bulls’ horns are 47.5–99 cm long and cows’ 37–64.5 cm.
- Yaks use them to defend themselves, especially against wolves, and bulls clash horns over mates.
Sources [1, 2]
14 pairs of ribs (most cattle: 13)
- The shoulder hump is not a fat store. It is built on extra-long spines that stick up from the backbone.
- Yaks have 14 pairs of ribs, one more than other cattle, which gives them a big chest for big lungs.
Sources [1, 2]
up to 70 cm long hair hanging from the flanks
- A fringe of very long, coarse hair hangs from the shoulders, flanks and belly, almost to the ground.
- Herders shear or comb their yaks once a year, in May–June.
- The coarse skirt hair is spun into ropes and woven into tents and bags.
Sources [1, 3, 4]
3 kinds of hair in one coat
- The coat mixes thick outer hair, middle-sized hair and a soft woolly down. Down fibres are thinner than 25 µm.
- In winter the share of soft down in the coat rises, like a yak putting on a thermal vest.
- Wild yaks are jet black or dark brown, often with a silver-grey stripe along the back.
Sources [2, 5, 6]
3.7 kg yak lungs (local cattle: 1.8 kg)
- At 5,000 m each breath holds about half the oxygen it would at sea level.
- In one study, yak lungs weighed 3.7 kg and local cattle lungs 1.8 kg. Yak hearts weighed 1.3 kg, cattle hearts 0.87 kg.
- A wide windpipe helps it move a lot of air, and the blood vessels in the lungs stay relaxed in thin air instead of squeezing tight as cows’ do.
Sources [2, 7, 8]
≈72% of the stomach is rumen
- Like a cow, a yak has a four-part stomach. The first part, the rumen, is a vat where microbes break down tough grass.
- In one yak breed the rumen made up about 72% of the stomach, against about 52% in a cattle breed.
- Yak rumen microbes make less methane gas than cattle microbes, which scientists think leaves more of the food’s energy for the yak.
Sources [2, 9]
2–3 cm short spring grass it can crop
- Like all cattle, a yak has no top front teeth, just a hard pad. It has 32 teeth in all.
- It wraps long grass with its rough tongue, but it can also nibble very short grass with its lips and teeth, as sheep do.
- Yaks hardly sweat: tests found sweat only on the muzzle.
Sources [1, 2]
- The ears are small and the body compact, which helps save heat. Yaks also have no loose dewlap under the neck.
- Wild yaks have a keen sense of smell. Their sight and hearing are thought to be weaker.
- Yaks are wary of wolves and people, and a startled herd quickly runs off.
Sources [1, 2]
7,200 m terrain pack yaks can cross
- Strong legs end in small, hard hooves with a narrow, sharp tip.
- The hooves press deep prints into the ground, which helps a yak control its speed going downhill.
- Yaks can swim across rapids. They plod on calmly instead of panicking.
- Unlike other cattle, yaks roll on the ground, like horses.
Sources [2]
- The tail ends in a long, bushy tassel of hair. Herders harvest it every two years.
- Yak tails have been used as fly whisks for nearly 2,000 years: the Roman poet Martial mentioned them.
- In Tibetan areas, a yak tail is a symbol of wealth and good luck.
Sources [3, 4, 6]

Real yaks

Photos from Wikimedia Commons. Some of them can repaint the 3D model.

Wild yakJet black to dark brown, with a silver-grey stripe along the back and grey-white hairs around the muzzle. Bulls are huge: about 1,000 kg.Vulnerable: roughly 15,000–20,000 left in the wildWild yaks behind a group of kiang (Tibetan wild asses) on a high plain. Photo: leej1118bj, CC BY 3.0
Wild yakJet black to dark brown, with a silver-grey stripe along the back and grey-white hairs around the muzzle. Bulls are huge: about 1,000 kg.Vulnerable: roughly 15,000–20,000 left in the wildA wild yak drawn for the book Across Thibet (1891), after a photograph. Photo: Gabriel Bonvalot (book); engraving after a photograph by Prince Henri d'Orléans, Public domain
Black domestic yakDark like its wild ancestor but much smaller: domestic bulls weigh about 235–594 kg. It lacks the wild yak’s grey muzzle hairs.Milk, butter, wool, pack work and dung for fuelA black yak moulting its winter coat, Tibetan Plateau, July. Photo: Tenace10, CC BY-SA 4.0
Black domestic yakDark like its wild ancestor but much smaller: domestic bulls weigh about 235–594 kg. It lacks the wild yak’s grey muzzle hairs.Milk, butter, wool, pack work and dung for fuelPack yaks on the Everest Base Camp trail, Nepal. Photo: TT4FT, CC BY-SA 4.0
White and piebald yakPatched black and white, or all white. The white-spotting genes most likely came from cattle long ago. About 2–3% of yaks are white.The Tianzhu White breed of Gansu, China: white hair dyes easily and is highly valuedA white domestic yak in Aba (Ngawa), Sichuan, China. Photo: Nyx Ning, CC BY-SA 3.0
White and piebald yakPatched black and white, or all white. The white-spotting genes most likely came from cattle long ago. About 2–3% of yaks are white.The Tianzhu White breed of Gansu, China: white hair dyes easily and is highly valuedPiebald and dark yaks by Lake Manasarovar, with Mount Kailash behind, Tibet. Photo: Jean-Marie Hullot, CC BY-SA 4.0
CalfBorn weighing 10–16 kg, mostly in May. Wild calves grow fast: at 3 months they weighed about 62.5 kg, against 33.6 kg for domestic calves.Mothers guard their calves fiercely and know them by smellA mother yak and her calf at a zoo in Massachusetts, USA. Photo: Eric Kilby, CC BY-SA 2.0
Two yaks butting heads on the Tibetan PlateauPhoto: Tenace10, CC BY-SA 4.0
A yak herd on summer pasture, Tibetan PlateauPhoto: Tenace10, CC BY-SA 4.0

Yak by the numbers

Measured by scientists, herders’ experts and zoos, with comparisons you can picture.

Weight: ≈1,000 kg; a wild bull; wild cows about 350 kg; Wild yak bull1,000 kgDairy cow (Holstein)624 kg; About 1.6× a dairy cow⁠[1, 21, 23]
Domestic yak: 235–594 kg; domestic bulls in China; cows 188–314 kg⁠[18]
Height: 1.5–2 m; a wild bull at the shoulder⁠[21, 1]
Horns: up to 99 cm; wild bull, along the outside curve⁠[1]
Home altitude: 3,000–5,500 m; where wild yaks live⁠[1]
Cold limit: −40 °C; still feeding and moving normally⁠[2]
Skirt hair: up to 70 cm; long hair hanging from the flanks⁠[1]
Lungs: 3.7 kg; against 1.8 kg in local cattle; Yak lungs3.7 kgCattle lungs1.8 kg; About twice as heavy⁠[2]
Pack load: 60–80 kg; carried 20–30 km a day⁠[17]
Lifespan: 26 years; the oldest on record, in captivity⁠[24]

Yak myths and facts

Tap Myth or Fact for each claim, then check the answer.

0 of 8 answered

“Yaks moo like cows.”
“Wild yaks are silent, which is why they are called Bos mutus, “mute ox”.”
“Wild yaks eat snow when the water freezes.”
“A yak’s hump is a store of fat, like a camel’s.”
“Yaks have extra-thick blood, packed with extra haemoglobin.”
“Yaks are uncomfortable in warm weather.”
“Yaks and cows can’t have calves together.”
“Yaks don’t get frostbite.”

Yak records

Superlatives and record holders, each checked against its source.

Heaviest pack load
300 kg
A domestic yak in Qinghai, China
at 4,100 m, 82% of the yak’s own body weight⁠[17]
Highest pack work
7,200 m
Pack yak steers
terrain that pack yaks can cross⁠[2]
Coldest grazing
−42 °C
Yaks in Naqu, Tibet
the coldest air temperature recorded where yaks still feed and move⁠[2]
Longest hair
up to 70 cm
Yak skirt
the fringe hanging from flanks and belly⁠[1]
Biggest horns
99 cm
Wild yak bull
longest horn in the species account, measured along the outside curve⁠[1]
Oldest yak
26.3 years
A yak in captivity
the record in the AnAge longevity database⁠[24]
Biggest yak country
≈94%
China
13.3 million of the world’s 14.2 million domestic yaks in a 2003 count⁠[6]
Rarest coat
≈2%
Golden wild yak
of wild yaks around the Aru Basin, northwestern Tibet, have a golden-brown coat⁠[1, 6]

A yak’s year

Life on the plateau follows the seasons: a long, hungry winter and a short, green summer.

November–April
Winter pastures
Herders move their yaks to lower, sheltered winter pastures. Yaks break through snow to reach old grass, and wild yaks eat snow for water.⁠[3, 2, 13]
Late winter
The hungry time
Grass is short and scarce. Adults can lose 25–30% of their weight, and heavy snowfalls can kill many animals.⁠[12, 3]
May
Calves arrive
Calves are born from March to August, most in May, weighing 10–16 kg. Wild calves in the Chang Tang arrive from mid-May to June.⁠[22, 18, 1]
May–June
Moult and shearing
The winter down loosens. Herders shear the yaks or comb out the soft down before it falls off.⁠[5, 3]
June–August
Summer feast
Herds move up to summer pastures. A yak can eat 28–38 kg of grass in 10 hours and regains its winter losses.⁠[3, 2, 12]
July–autumn
Breeding season
High on the plateau, cows come into season from about July. Bulls grunt, wallow and show off side-on to rivals.⁠[22, 1]
Autumn
Winter coat
Thick hair and a soft woolly down grow in, ready for a winter of −30 °C and colder.⁠[5, 2]

Wild yak vs domestic yak vs cow

Domestic yaks descend from wild yaks. Both are close cousins of cattle, but built for a very different world.

Wild yak vs domestic yak vs domestic cow (Holstein)
	Wild yak	Domestic yak	Cow (Holstein)
Scientific name⁠[1, 11]	Bos mutus	Bos grunniens	Bos taurus
Where it lives⁠[1, 12, 11]	Tibetan Plateau, 3,000–5,500 m	Herded mostly at 3,000–5,000 m	Farms worldwide, mostly in the lowlands
Weight⁠[1, 18, 23]	Bulls ≈1,000 kg; cows ≈350 kg	Bulls 235–594 kg; cows 188–314 kg	Dairy cows ≈624 kg
Shoulder height⁠[21, 1, 18, 23]	Bulls 1.5–2 m	Bulls 117–138 cm	Dairy cows ≈149 cm
Coat⁠[1, 19]	Long skirt and woolly down; black-brown	Same coat; black, brown, piebald or white	Short hair
Voice⁠[1, 14]	Grunts; bulls bellow	Grunts	Moos
Pregnancy⁠[1, 22, 26]	258–270 days	≈258 days	≈279 days
How many⁠[1, 12, 27]	≈15,000–20,000	≈16 million	≈1.58 billion cattle of all kinds
Red List⁠[28, 29]	Vulnerable	Not evaluated (domestic)	Domestic animal

Domestic yaks were tamed from wild yaks roughly 7,300 years ago.

Are wild yaks endangered?

Domestic yaks number in the millions, but wild yaks are rare and listed as Vulnerable.

IUCN Red List

Vulnerable (VU)

Roughly 15,000–20,000 wild yaks remain, almost all on the Tibetan Plateau in China. In Nepal they were thought to be gone until two were seen in Upper Humla in 2014.⁠[28, 30, 1, 12, 31]

IUCN Red List, assessed 2016

Threats

Poaching
Wild yaks were hunted heavily in the past and illegal hunting still happens. In Hoh Xil, female herds moved to steeper slopes after heavy poaching.⁠[1, 13, 32]
Mixing with domestic yaks
Wild and domestic yaks interbreed, so domestic genes spread into wild herds. Scientists call this a major long-term threat.⁠[31, 32]
Competition and lost habitat≈31% unprotected
Livestock compete with wild yaks for grass, and their habitat is being damaged and broken up. About 31% of wild yak habitat lies outside protected areas.⁠[32]
Climate change
Wild yaks live between the tree line and the glaciers. As it warms, parts of their range are expected to shrink and split up.⁠[33]

What’s helping

Full legal protection
Wild yaks have top-level (Class I) protection in China, and hunting has been banned since the early 1990s. International trade has been banned under CITES Appendix I since 1975.⁠[1, 34]
Big reserves
The Chang Tang, Arjin Shan and Hoh Xil reserves protect the core of the wild yak’s range.⁠[1, 32]
Safe places for the future≈64%
Scientists have mapped climate refuges, covering about 64% of today’s habitat, that should still suit wild yaks in 2070.⁠[33]

Yak relatives and forms

Domestic yakNot Evaluated
Not assessed by the IUCN, because it is a domestic animal. About 16 million live across the high mountains of Asia.⁠[29, 12]

Yak quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

Why is the domestic yak called Bos grunniens?

Bos grunniens field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

Wild yaks are herbivores that graze on tough grasses and hardy plants found in harsh mountain environments.

Primary Foods

Grasses
Sedges
Mosses
Lichens
Alpine Herbs
Foraging Method: Grazing

Ecological connections

Snow LeopardHunts
A primary predator of young or vulnerable yaks.
Grey WolfHunts
Wolves often hunt yaks in packs, targeting weaker individuals.
Himalayan VultureEats
Scavenges on the carcasses of yaks that have died.

Safety

Danger 3/5 · Moderate

Always keep a safe distance from yaks, as they can be big and strong.

Traits

Collections

Mammals

Classification

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Bovidae
Genus: Bos

Also known as

Dri (Tibetan for a female yak) · Yag (Tibetan for a yak bull) · “Boat of the plateau” (nickname for pack yaks) · Grunting Ox

Sources for these yak facts

35 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Bos grunniens?

Compare ears, muzzle, tail, feet and coat markings. Size is hard to judge without something nearby for scale, and young mammals may not have adult coloring yet. Mammal Identifier: upload a photo and compare the visible details.

How long is Bos grunniens?

250-330 cm

How much does Bos grunniens weigh?

300-1000 kg

How long does Bos grunniens live?

15-25 years

How fast can Bos grunniens move?

40 km/h

What does Bos grunniens eat?

Wild yaks are herbivores that graze on tough grasses and hardy plants found in harsh mountain environments.

Where is Bos grunniens usually found?

Mountain regions

How does Bos grunniens hunt?

Grazing

Do yaks moo?

No. Yaks grunt, which is why the domestic yak is called Bos grunniens, the “grunting ox”. In the breeding season wild yaks also bellow, squeak and cry.

Are yaks dangerous?

Yaks are big, strong and easily startled. Cows with newborn calves can attack, and wild bulls have charged people on remote roads. Never walk up to a yak, keep a wide distance, stay with an adult and let herders lead.

How cold can a yak survive?

Yaks feed and move normally at −30 to −40 °C, and they graze where −42 °C has been recorded. Their three-layer coat, thick skin and lack of sweating keep heat in. No case of frostbite has been recorded.

How high do yaks live?

Wild yaks live at about 3,000–5,500 m on the Tibetan Plateau, between the tree line and the glaciers. Domestic yaks are herded mostly at 3,000–5,000 m, and pack yaks can cross terrain at 7,200 m.

What is the difference between a wild yak and a domestic yak?

Wild yaks (Bos mutus) are much bigger, bulls about 1,000 kg against 235–594 kg for domestic bulls, and are always dark with grey muzzle hairs. Domestic yaks (Bos grunniens) were tamed from wild yaks roughly 7,300 years ago and come in more colours.

What are yaks used for?

Herders use yaks for milk (drunk in milk tea or made into butter and cheese), meat, wool and down, ropes and tents from the long hair, pack transport and dried dung, the main fuel on the treeless plateau.

How many wild yaks are left?

Roughly 15,000–20,000, almost all in China. The wild yak is listed as Vulnerable on the IUCN Red List. Domestic yaks number about 16 million.

Can yaks and cows breed?

Yes. Yak–cattle hybrids are called dzo in Tibetan areas and chauri in Nepal. The female hybrids can have calves, but the males are sterile.

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