Sheep
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? Sheep |
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 Bighorn
Sheep
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Species
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A sheep is an individual of any of the eight woolly mammal species that comprise the genus Ovis, part of the goat antelope subfamily. All the sheep are bovids (members of the family Bovidae) and ruminants, meaning they chew cud. The domestic sheep is thought to be descended from the wild moufflon of central and southwest Asia. Male sheep are called rams— or wethers if castrated—females ewes, and young lambs. Members of the genus are highly gregarious.
Sheep are usually stockier than other bovines and some have horns which are more divergent than those of goats. Sheep have scent glands on the face and hind feet. Communication through the scent glands is not well understood but is thought to be important for sexual signaling. Males can smell females which are fertile and ready to mate, and rams mark their territories by rubbing scent on to rocks. They have a four-chambered stomach which plays a vital role in digesting, regurgitating, and redigesting food. Domestic sheep are important for their wool, milk, and meat (which is called mutton or lamb).
Sheep species
There are at least eight species of sheep:
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O. ammon | Mountain sheep ( Argali) |
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O. aries | Domestic sheep |
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O. canadensis | Bighorn sheep |
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O. dalli | Dall Sheep |
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O.
musimon,
or O. ammon musimon |
European Mouflon |
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O. nivicola | Snow sheep |
| O. orientalis | Asiatic Mouflon | |
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O. vignei | Urial |
Hybrids with goats
Although sheep and goats seem similar and can be mated together they belong to different genera. Goats are caprinae and have 60 chromosomes while sheep are ovinae and have 54 chromosomes. At Botswana Ministry of Agriculture, a ram that was kept with a nanny goat impregnated the goat resulting in a live offspring that had 57 chromosomes. This was called "The Toast of Batswana". The hybrid is intermediate between the two parent species in type. It has a coarse outer coat, a woolly inner coat, long goat-like legs and a heavy sheep-like body. Although infertile, the Toast of Batswana was castrated to prevent unwanted sexual behaviour because it continually mounted the sheep and goats sharing its enclosure.
In 1969, Australian farmer Dick Lanyon, who farmed near Melbourne, Australia, kept a billy-goat among his sheep to scare off foxes during the lambing season. In September of the same year, he claimed to have dozens of ‘lambs’ which were sheep-goat hybrids. The goat was locked up while scientists examined the supposed hybrids. As no more was heard of this case, it is believed that the lambs were pure-bred sheep.
There is a long-standing belief in sheep/goat hybrids which is due to the animals' resemblance to each other. Some primitive varieties of sheep may be misidentified as goats. In "Darwinism An Exposition Of The Theory Of Natural Selection With Some Of Its Applications" (1889), Alfred Russel Wallace wrote:
Supposedly, most goat-sheep hybrids die as embryos (the famous geep is a chimera, not a hybrid). Hybrid male mammals are often sterile due to a phenomenon called Haldane's Rule. The Haldane phenomena may apply even when the parent species have the same number of chromosomes as in most cat species hybrids. It sometimes does not apply when the species chromosome number is different as in wild horse (chromosome number = 66) and domestic horse (chromosome number = 64) hybrids. Hybrid female fertility tends to decrease with increasing divergence in chromosome similarity between parent species. Presumably, this is due to mismatch problems during meiosis and the resulting production of eggs with unbalanced genetic complements.