Sheep - biology.

Sheep - biology. I INTRODUCTION Sheep, common name for a collection of grazing mammals that may be either wild or domesticated; the domesticated varieties are the most widely distributed kind of domestic animal, found in nearly all countries. Wild species are found in some areas of the world: the bighorn in western North America; Dall sheep in northern Canada and Alaska; the mouflon in Mediterranean countries; the Asian mouflon in western Asia; the urial Afghanistan and Pakistan; and the argali in eastern Asia. Sheep were probably domesticated about 11,000 years ago in what is now northern Iraq, and they are thought to have descended primarily from the mouflon, although recent evidence suggests that species such as the Asian mouflon contributed to some of the modern breeds. II CHARACTERISTICS Sheep are even-toed, hoofed animals. They are cud-chewing animals with the upper incisor teeth missing and with a four-compartmented stomach (see Artiodactyl). They have paired, hollow, unbranched horns that are not shed. The horns of the adult male, or ram, are massive and spirally curved. The horns of the adult female, or ewe, are short and only slightly curved. Sheep typically have a long, fairly narrow muzzle and pointed ears. The length of the head and body averages about 1.5 m (about 5 ft), with a short tail, and an adult may weigh 75 to 200 kg (165 to 440 lb). In the wild, the animals are nimble runners and climbers. The female bears up to three young after a gestation period of about 150 days. Sheep live as long as 20 years. Besides providing pelts and wool for clothing and carpets, meat in the form of lamb and mutton, and milk for drinking and cheesemaking, sheep are used to a limited extent as pack animals, and the wild species are hunted as game. Several distinct types and more than 800 breeds of domesticated sheep have been developed. The breeds are adapted to environments that range from desert to tropical conditions. III FINE-WOOL BREEDS Sheep bred for their fine wool account for nearly half the world sheep population. They are adapted to semiarid conditions and are characterized as medium in size, with the ability to produce large amounts of wool fibers 20 micrometers or less in diameter. Found extensively in Australia, New Zealand, South America, and the western United States, most sheep of this type belong to the merino breed, which originated in the Mediterranean area and became concentrated in Spain. The breed, however, has been modified and adapted to the conditions prevalent in various countries, and the different subtypes are usually called merinos combined with the name of their adopted country--for example, the Australian merino. The Rambouillet, similar to the merino, is the other major breed of fine-wool sheep. IV MUTTON-TYPE SHEEP Mutton-type sheep, which consist of medium- and long-wool breeds, have been bred primarily for their meat. They account for about 15 percent of the world sheep population. Among the medium-wool breeds are the Suffolk, Hampshire, Shropshire, Southdown, Dorset, Isle-de-France, Cheviot, and Oxford; and long-wool breeds, the largest of all breeds, include the Leicester, Lincoln, Cotswold, and Romney Marsh. In the United States, long-wool breeds are used extensively as sires with fine-wool and crossbred females for the production of market lambs. Many attempts have been made to obtain the superior wool characteristics of fine-wool breeds with the meat-producing abilities of other breeds. These have resulted, in recent times, in the development of several new breeds: the Corriedale (merino-Leicester-Lincoln); Columbia (Rambouillet-Lincoln); Targhee (Rambouillet-Lincoln); Romeldale (Romney Marsh-Rambouillet-Corriedale); and Polworth (merino-Lincoln). V SHORT-TAILED SHEEP The northern short-tailed sheep, similar to the medium-wool type, are found primarily in Scandinavia. They account for about 3 percent of the world sheep population and are characterized by high reproduction rates. At present they are used experimentally to a limited extent in the United States for crossbreeding, primarily to increase the number of lambs born to each breeding female. VI FAT-TAILED SHEEP These sheep are so named because they can store large amounts of fat in the tail and the region of the rump. They are kept primarily for their milk-producing ability, which is higher than that of other types; their wool, however, is coarse and long and is used primarily for making carpets. Fat-tailed sheep are found mainly in the extremely arid regions of Africa, the Middle East, and Asia, and they represent about 25 percent of the world sheep population. The major breeds are the Awassi, Bakhtiari, Karakul, and Karamon. The pelts of the newborn Karakul lambs are used for the manufacture of the so-called Persian fur coats. VII HAIRED SHEEP Domesticated sheep on the whole are much more woolly than their wild allies, but some breeds lack wool and are covered with hair. They are found primarily in tropical regions and are used primarily for meat. Among the breeds of this type are the Black-bellied Barbados, Blackhead Persian, and the Peliquey. VIII DISTRIBUTION In 2006 the world sheep population was estimated at 1.10 billion head. Based on numbers, the leading sheep countries, in descending order, were China (173,899,000), Australia (100,100,000), India (62,850,000), Iran (52,219,000), Sudan (49,797,000), New Zealand (40,107,000), United Kingdom (34,722,000), South Africa (24,983,000), Turkey (25,304,000), and Pakistan (25,400,000). The United States had 6,230,000 sheep, less than 1 percent of the world total. In the United States, the sheep industry is centered in the semiarid western half of the country. In 2003 the leading sheep states were Texas (1,040,000), California (730,000), Wyoming (460,000), Colorado (380,000), and South Dakota (380,000). Other major states were Utah, Montana, Oregon, Idaho, New Mexico, and Iowa. IX PRODUCTION Various systems have evolved in sheep production. In the western United States, large bands are grazed on the open range under the control of shepherds. Usually fine-wool or crossbred ewes, they are bred to rams of the Down breeds for the production of lambs for meat. The bands may be moved from place to place to take advantage of cheap feeds and natural forage. Similar operations are used on lands with developed pastures. If abundant forage is available, the lambs may be marketed directly after weaning. If the lambs have not reached marketable condition, they may be moved to feedlots and given additional food before they are sold. Some breeders specialize in the production of purebred animals for use in the large commercial flocks. These purebred flocks are considerably smaller in size, and genetic selection for superior productive traits is emphasized. The income from such flocks is derived primarily from the sales of the superior animals, especially the rams, to commercial breeders. In the midwestern United States, sheep enterprises may consist of a farm flock containing small numbers of animals. The flocks are maintained primarily as an auxiliary unit to utilize the by-products of other producing units, particularly grain crops. See Animal Husbandry. Scientific classification: Sheep belong to the suborder Ruminantia of the order Artiodactyla. They make up the genus Ovis in the family Bovidae. The domesticated sheep is classified as Ovis aries, the bighorn sheep as Ovis canadensis, and dall's sheep as Ovis dalli. The mouflon is classified as Ovis musimon, the Asian mouflon as Ovis orientalis, the Urial as Ovis vignei, and the argali as Ovis ammon. Contributed By: Perry Thomas Cupps Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.