Sheep

I

Introduction

Sheep, common name for a collection of grazing mammals that may be 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 mouflon in Mediterranean countries; the Asian mouflon in western Asia; the bighorn in western North America; Dall sheep in northern Canada and Alaska; the urial in 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 were thought to be descended primarily from the Mediterranean mouflon, but 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 (artiodactyls). They are cud-chewing animals (ruminants) with the upper incisor teeth missing and with a four-chambered stomach. 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 (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. Sheep are prone to a number of diseases and parasites, most particularly the scrapie virus, which is caused by the infectious agent prion. It causes the degradation of brain tissue.

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 semi-arid conditions and are characterized as medium in size, with the ability to produce large amounts of wool fibres about 20 micrometres 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 per cent of the world’s 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 cross-bred 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).