See M. E. Ensminger, Sheep and Wool Science (4th ed. 1970); N. D. May, The Anatomy of the Sheep (3d ed. 1970); publications of the U.S. Dept. of Agriculture.
Open upright woody shrub (Kalmia angustifolia) of the heath family. Growing 1–4 ft (0.3–1.2 m) high, it has glossy, leathery, evergreen leaves and showy pink to rose flowers. Like other Kalmia species (including mountain laurel) and other members of the heath family, it contains a poison (andromedotoxin). In northwestern North America, where these plants occur, livestock (especially sheep) that graze on nonfertile soils of abandoned pastures and meadows may ingest enough of the plant to become poisoned, potentially fatally.
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Ruminants (bovid genus Ovis) that have scent glands in the face and hind feet. Horns, if present, are more divergent than those of goats. Species range from 80 to 400 lb (35 to 180 kg). The coat of wild species consists of outer hair underlain by wool. Sheep graze in flocks, preferably on short, fine grasses and legumes. They have been domesticated from at least 5000 BC in the Middle East, Europe, and Central Asia. Most domesticated breeds produce fine wool; the few that produce only hair or coarse or long wool are generally raised for meat. The flesh of mature sheep is called mutton; that of immature sheep is called lamb.
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Bighorn sheep (Ovis canadensis).
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Mountain range, southern Montana and northern Wyoming, U.S. It is a range of the northern Rocky Mountains extending 120 mi (193 km), rising abruptly 4,000–5,000 ft (1,200–1,500 m) above the Great Plains and Bighorn Basin. The highest summit is Wyoming's Cloud Peak, at 13,165 ft (4,013 m). Bighorn National Forest covers part of the range. On Medicine Mountain is the Medicine Wheel, a prehistoric stone-spoked circle 70 ft (20 m) in diameter.
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The cell used as the donor for the cloning of Dolly was taken from a mammary gland, and the production of a healthy clone therefore proved that a cell taken from a specific body part could recreate a whole individual. More specifically, the production of Dolly showed that mature differentiated somatic cells in an adult animal's body could under some circumstances revert back to an undifferentiated pluripotent form and then develop into any part of an animal. As Dolly was cloned from part of a mammary gland, she was named after the famously busty country western singer Dolly Parton.
In the previous year, the same team had produced cloned sheep from the embryonic cells, but this was not seen as a breakthrough since adult cloned animals had been produced from embryonic tissue as long ago as 1958, using cells from the frog Xenopus laevis.
Dolly was the first clone produced from a cell taken from an adult animal. However, this cloning process is still highly inefficient, with Dolly the only lamb that survived to adulthood from 277 attempts. She is also recognised as one of the major stepping stones in the development of modern biology. Wilmut, who led the team that created Dolly, announced in 2007 that the nuclear transfer technique may never be sufficiently efficient for use in humans.
However, some have speculated that a contributing factor to Dolly's death was that she could have been born with a genetic age of six years, the same age as the sheep from which she was cloned. One basis for this idea was the finding that Dolly's telomeres were short, which typically is a result of the aging process. However, the Roslin Institute have stated that intensive health screening did not reveal any abnormalities in Dolly that could have come from advanced aging.
Cloning may eventually become a viable tool for preserving endangered species and could be important in the future production of transgenic livestock. However, animal conservation professionals point out that cloning does not alleviate the problems of loss of genetic diversity (see inbreeding) and habitat, and so must be considered an experimental technology for the time being, and all in all would only rarely be worth the cost, which on a per-individual basis far exceeds conventional techniques such as captive breeding or embryo transfer.