Sunday, 3 April 2016

Bovines: The Other Domesticated Species

Domestic yak
The large physical size and herd mentality of bovines makes them ideal subjects for domestication, especially as beasts of burden. So much so in fact, that not only have true cattle been domesticated at least twice, but no less than four other species of bovine have also been domesticated on a wide scale since ancient times. (I am ignoring here the fact that bison, for example, have been farmed for their meat in recent decades, and am only considering "traditionally" domesticated animals). Unlike true cattle, the wild ancestors of these animals remain alive - all four of them in Asia.

One of the more familiar of these "other" domesticated bovines is the yak (Bos grunniens), which is descended from... well, the wild yak (Bos mutus). Today, wild yak are found only on the Tibetan Plateau, although in medieval times they may have lived much further north and west. One small population is known to cross the border into Ladakh in far northern India at certain times of the year, but they are otherwise extinct outside of China, having vanished from Nepal as recently as the 1990s.

Wild yak are large animals, with the bulls standing 170 to 200 cm (5'6" to 6'6") high at the shoulder, and weighing anything from 535 kg up to a tonne (1,200 to 2,200 lbs). This is approximately the same size as a male bison, although it's interesting to note that the females are much smaller, weighing only about a third as much as the males, a difference far more dramatic than that in the American species. Such a large animal, of course, requires rather a lot of feed, which likely explains why domestic yak have been bred to be quite a bit smaller.

Even by the standards of bovines, yak are indiscriminate grazers, eating just about anything they come across. A combination of thick lips, grinding teeth, and a particularly rough tongue allow them to eat much more scrappy vegetation than cattle normally prefer, alongside the longer grass that forms much of their relatives' diets. Given where they live, this is likely a necessity, since, for much of the year there won't be a lot of choice as to what they eat anyway. In order to extract as much nutrition as possible from what is often quite low quality roughage, yaks retain food in their guts for significantly longer than true cattle. They also have a dramatically different population of fermenting bacteria in the first chamber of their stomach, although it's not clear exactly how, or even if, this really helps them.

However, living on the Tibetan Plateau presents more problems than a lack of high quality food; it is also very cold and very high up. Their squat, powerful, shape helps retain heat, and this is helped by a remarkably thick pelt of long hair, which, in the wild animal, is usually a dark black or brown in colour, also helping to absorb whatever warmth is available. The tiny muscle fibres in the skin that normally fluff hair up to retain body heat are also said to be unusually strong in yak.

Indeed, yak are so well adapted to the cold that they become uncomfortable if the temperature rises above about 15°C (59°F), something that rather limits their employment as domestic animals outside of Tibet. (Having said which, there have been some attempts to farm them in Canada and even the US). In particular, yak possess virtually no functioning sweat glands, with just a small number on the nose.

While domestic yak are farmed at much lower altitudes, in recent decades, the surviving wild population has retreated ever further up the mountains, and they are now commonly only found in the treeless wastes and near-desert conditions above 4,500 metres (14,800 feet). The thin air at these altitudes also requires special adaptations, and yak are said to have unusually large hearts and lungs, as well as an unusual form of haemoglobin that allows them to transport more oxygen around the body.

As an aside, the scientific name Bos mutus literally means "silent cow". It's possible that Przewalski gave them this name because they don't go "moo", although they do an awful lot of grunting instead, so it's hardly accurate.

The history of the domestication of yak is less well understood than that of true cattle. It likely first occurred over 4,000 years ago, during Tibet's Neolithic period, and has also been tentatively linked with the Longshan Culture along the Yellow River. Despite a few, largely experimental, introductions to other parts of the world, the great majority of domestic yak are still found in the same general area, across western China, Mongolia, Nepal, and in the border regions of neighbouring countries.

They are raised primarily as beasts of burden and as a source of milk. Although the amount of milk produced is very low compared with the staggering output of modern dairy cattle (150 to 500 kg per lactation, compared with well over 10,000 kg), it is nonetheless an important part of the local culture, and, helped by its very high fat content, frequently made into butter and cheese. Yak racing is also a traditional sport, and, when you live in a treeless waste, yak dung is about all you have to make a fire out of.

Wild yaks live in small single-sex herds that join up in the July to September breeding season. At this time, the males engage in a vigorous and aggressive rut, fighting to establish dominance. Largely, it has to be said, at the instigation of the females, who apparently like this sort of thing. Unusually, they also wallow on patches of dry ground, often scent marking it with urine and dung. Among their close relatives, American bison are the only other animals to do this, and it may be notable that the latter are thought to be closer in evolutionary terms to yak than to any other species. Pregnancy is a little shorter than in true cattle, varying from 258 to 270 days, and almost always results in the birth of a single calf.

Yak are also capable of cross-breeding with domestic cattle, and this has been practised since ancient times. Conception rates are relatively low, although, since the sperm seem perfectly capable of fertilising the eggs, and the initial stages of embryonic development seem normal, it isn't clear why. The male offspring of such unions are, like mules, sterile, although the females are not, making it possible to continue breeding them with regular cattle for multiple generations. These hybrids, called dzo if male, and dzomo if female, are typically larger than pure yak, and the females produce more milk, while simultaneously being better able to tolerate cold climates than true cattle, and less disturbed by heat than yak. There have also been some attempts to breed yak with bison, but these did not work as well as might be expected, and they were abandoned in 1928.

Male gaur
Although yak are not commonly seen in the west, their existence is at least well known. This is likely rather less true of the gaur (Bos gaurus), which is found in the wild in southern and central India, in Nepal, and across Southeast Asia from Myanmar to Malaysia and Vietnam. It is often said to be the largest of all bovines, although the point is arguable, as the bulls are about the same weight as those of bison or yak, and the females notably smaller than those of bison.

They are, however, taller at the shoulder, with the males reaching as high as 220 cm (7' 3"). This is aided, in part, by the presence of a muscular hump behind the neck, which, like the similar hump in yak, is formed by particularly high extensions of the vertebrae, which in the gaur also extend as a ridge down to the mid-back. Other distinctive features include the heavy, curving, horns, which are present in both sexes, and white "socks" on their feet that offset the otherwise black colour of their bodies.

The domesticated form of the gaur (Bos frontalis) is known variously as a gayal or mithun, among other local terms. In fact, it is debatable as to whether gayals really are domesticated gaurs in the strict sense; some researchers have claimed that they descend from a related species that is otherwise unknown and extinct, or else that they are hybrids of gaur and true cattle. Certainly both gayal and wild gaur can crossbreed with domestic cattle, although any resulting males are infertile, possibly because their parents have differing numbers of chromosomes.

Gayal are domesticated primarily for their meat, although they also produce relatively small quantities of highly nutritious milk and are said to produce a superior form of leather. They are somewhat smaller than wild gaur, and it has been noted that the breeds with the lowest natural levels of growth hormone are also the most docile. Since they are largely left to their own devices before being culled, and are not bred intensively, they are sometimes described as "semi-domesticated" animals, rather than by the more definitive term.

Wild gaur are generally forest animals, although they are adaptable, and can still thrive in other habitats. In modern times they are often found in hilly terrain up to 3,000 metres (9,800 feet) in altitude as more lowland regions are subject to advancing agriculture. Although probably not to the same extent as in yak, they can extract more nutrition from poor quality food than can domestic cattle. In addition to grass and shrubs, they eat a significant quantity of bamboo and scrape the bark off trees. Unsurprisingly, they will eat farm crops should they happen to get into a field, which, combined with the fact that they are hunted for their meat, has led to a rapidly declining population in many parts of their range.

Attempts to counter this decline have included setting up nature reserves and the like, but also transplanting gaur embryos into cattle in the hope of raising young without the need for captive mothers. Despite initial promise, this has not proved particularly successful. In the wild, gaur seem to breed at different times of the year depending on their locality, perhaps linked to the local weather patterns. Males, which remain apart for the remainder of the time, join the female herds during the breeding season. There they compete with one another by clashing horns, although once they find a receptive female they court her more actively, hanging around for a few days and licking her until she seems ready.

Gaur give birth to single calves after a 275 day pregnancy, which is about the same as that for domestic cattle. Herds are small, at least these days, with no more than twelve members, and their membership changes throughout the year as individual females come and go.

Before I look at the remaining domesticated species, however, it is time to turn away and consider the closest living relative of the yak: the American bison.

[Photos by Dennis Jarvis and Dinesh Kannambadi, from Wikimedia Commons. Cladogram adapted from Bibi 2013 and Stankowich 2009.]


  1. If the European bison is closer to domestic cattle, should it deserve its own genus? Bonasus bonasus? Or back to Bos bonasus?

    1. I will be discussing that very question in the next bovine post! But, yes, if the European bison is closer to domestic cattle (and I believe this is the current consensus, if not definitively settled) it's back to being /Bos/...

    2. It will depend on the extinct bovines in this clade. Perhaps more than one genus.How did Pelorovis fit in this tree?

    3. I remember a split from Bison schoetensacki, one branch to bison via antiquus; another one to bonasus via priscus.