Sheep (: sheep) or domestic sheep (Ovis aries) are a domesticated ruminant mammal typically kept as livestock. Although the term sheep can apply to other species in the genus Ovis, in everyday usage it almost always refers to domesticated sheep. Like all ruminants, sheep are members of the order Artiodactyla, the even-toed ungulates. There are around 1.2 billion domestic sheep as of 2019, making them easily the most common species of sheep. An adult female is referred to as a ewe ( ); an intact male as a ram, occasionally a tup; a castrated male as a wether; and a young sheep as a lamb.
Sheep are most likely descended from the wild mouflon of Europe and Asia, with Iran being a geographic envelope of the domestication center. One of the earliest animals to be domesticated for agricultural purposes, sheep are raised for fleeces, meat (lamb, hogget, or mutton), and sheep milk. A sheep's wool is the most widely used animal fiber, and is usually harvested by shearing. Ovine meat is called lamb and mutton, with lamb describing meat from younger animals and mutton meat from older ones. Sheep continue to be important for wool and meat today, and are also occasionally raised for pelts, as dairy animals, or as model organisms for science.
Sheep husbandry is done throughout the majority of the inhabited world. It was central to agriculture and textiles throughout Eurasia for millennia. In the 21st century, Australia, New Zealand, nations of southern and western South America, South Africa, and the British Isles are most closely associated with sheep production. More recently, China and India host among the largest flocks by absolute count, if as a smaller proportion of their economy.
There is a large lexicon of unique terms for sheep husbandry which vary considerably by region and dialect. Use of the word sheep began in Middle English as a derivation of the Old English word . A group of sheep is called a flock. Many other specific terms for the various life stages of sheep exist, generally related to lambing, shearing, and age.
As a key animal in the history of farming, sheep have an entrenched place in human culture. Sheep terminology and idiom are common in language and symbolism. As livestock, sheep are most often associated with pastoral, Arcadian imagery. Sheep figure in many mythologies—such as the Golden Fleece—and major religions, especially the Abrahamic traditions. In both ancient and modern religious ritual, sheep are used as sacrificial animals.
History
The exact line of descent from wild ancestors to domestic sheep is unclear. The most common hypothesis states that Ovis aries is descended from the Asiatic (O. gmelini) species of mouflon; the European mouflon (Ovis aries musimon) is a direct descendant of this population. Sheep were among the earliest animals to be domesticated by humankind (along with dogs, which were domesticated 10 to 20 thousand years earlier); the date of domestication is estimated to fall between 11,000 and 9000 BC in Mesopotamia, from which it spread to Mehrgarh in the Indus Valley around 7000 BC. The rearing of sheep for secondary products, and the resulting breed development, began in either southwest Asia or western Europe. Initially, sheep were kept for meat, milk, and skins rather than fleece. Archaeological evidence from statuary found at sites in Iran suggests that selection for woolly sheep may have begun around 6000 BC, while the earliest woven wool garments have been dated to around 4000 BC, two thousand years later.
Sheep husbandry spread quickly in Europe. Excavations show that in about 6000 BC, during the Neolithic period, the Castelnovien people in Châteauneuf-les-Martigues, near present-day Marseille in the south of France, were among the first Europeans to keep domestic sheep.Max Escalon de Fonton, L'Homme avant l'histoire, p. 16–17, in Histoire de la Provence, Editions Privat, Toulouse, 1990. See also F. Bourdier, Préhistoire de France (Paris, 1967) and G. Bailloud, Les civilisations Néolithiques de la France (Paris, 1955). Practically from its inception, ancient Greek civilization relied on sheep as primary livestock, and the Greeks were even said to name individual animals. Ancient Romans kept sheep on a wide scale, and were an important agent in the spread of sheep raising. Pliny the Elder, in his Natural History (), speaks at length about sheep and wool. European colonists spread the practice to the New World from 1493 onwards.
Characteristics
Domestic sheep are relatively small ruminants, usually with a crimped hair called wool and often with horns forming a lateral spiral. They differ from their wild relatives and ancestors in several respects, having become uniquely neotenic as a result of selective breeding by humans. A few primitive breeds of sheep retain some of the characteristics of their wild cousins, such as short tails. Depending on breed, domestic sheep may have no horns at all (i.e. polled), or horns in both sexes, or in males only. Most horned breeds have a single pair, but a few breeds may have several horns, such as Jacob sheep.
Another trait unique to domestic sheep as compared to wild ovines is their wide variation in color. Wild sheep are largely variations of brown hues, and variation within species is extremely limited. Colors of domestic sheep range from pure white to dark chocolate brown, and even spotted or piebald. Sheep keepers also sometimes artificially paint "smit marks" onto their sheep in any pattern or color for identification. Selection for easily dyeable white fleeces began early in sheep domestication, and as white wool is a dominant trait it spread quickly. However, colored sheep do appear in many modern breeds, and may even appear as a recessive trait in white flocks. While white wool is desirable for large commercial markets, there is a niche market for colored fleeces, mostly for handspinning. The nature of the fleece varies widely among the breeds, from dense and highly crimped, to long and hairlike. There is variation of wool type and quality even among members of the same flock, so wool classing is a step in the commercial processing of the fibre.
Depending on breed, sheep show a range of heights and weights. Their rate of growth and mature weight is a heritable trait that is often selected for in breeding. Ewes typically weigh between , and rams between . When all deciduous teeth have erupted, the sheep has 20 teeth. Mature sheep have 32 teeth. As with other ruminants, the front teeth in the lower jaw bite against a hard, toothless dental pad in the upper jaw. These are used to pick off vegetation, then the rear teeth grind it before it is swallowed. There are eight lower front teeth in ruminants, but there is some disagreement as to whether these are eight incisors, or six incisors and two incisor-shaped canines. This means that the dental formula for sheep is either or There is a large diastema between the incisors and the molars.
In the first few years of life one can calculate the age of sheep from their front teeth, as a first and second set of milk teeth are replaced by larger adult teeth. The full set of eight adult front teeth is complete at about four years of age. These teeth are then gradually ground down as sheep age and feed on pasture, making it harder for them to feed and hindering their health over time. For this reason, domestic sheep on normal pasture begin to slowly decline from four years on. The life expectancy of a sheep is 10 to 12 years, though some sheep may live as long as 20 years. Ranchers often consider culling sheep not raised for meat around 6 years of age, although extra pasture or the sheep being an exceptional producer can encourage their handlers to continue keeping them.
Sheep have good hearing, and are sensitive to noise. Sheep have horizontal slit-shaped pupils, with excellent peripheral vision; with visual fields of about 270° to 320°, sheep can see behind themselves without turning their heads. Many breeds have only short hair on the face, and some have facial wool (if any) confined to the poll and or the area of the mandibular angle; the wide angles of peripheral vision apply to these breeds. A few breeds tend to have considerable wool on the face; for some individuals of these breeds, peripheral vision may be greatly reduced by "wool blindness", unless recently shorn about the face. Sheep have poor depth perception; shadows and dips in the ground may cause sheep to baulk. In general, sheep have a tendency to move out of the dark and into well-lit areas, and prefer to move uphill when disturbed. Sheep also have an excellent sense of smell, and, like all species of their genus, have scent glands just in front of the eyes, and interdigitally on the feet. The purpose of these glands is uncertain, but those on the face may be used in breeding behaviors. The foot glands might also be related to reproduction, but alternative functions, such as secretion of a waste product or a scent marker to help lost sheep find their flock, have also been proposed.
Comparison with goats Sheep and goats are closely related: both are in the subfamily Caprinae. However, they are separate species, so hybrids rarely occur and are always infertile. A hybrid of a ewe and a buck (a male goat) is called a sheep-goat hybrid, known as geep. Visual differences between sheep and goats include the beard of goats and divided upper lip (philtrum) of sheep. Sheep tails also hang down, even when short or docked, while the short tails of goats are held upwards. Also, sheep breeds are often naturally polled (either in both sexes or just in the female), while naturally polled goats are rare (though many are polled artificially). Males of the two species differ in that buck goats acquire a unique and strong odor during the rut, whereas rams do not.
Breeds
The domestic sheep is a multi-purpose animal. More than 200 breeds are recognized, created and bred to serve diverse purposes. Some sources who use the term more freely give counts exceeding a thousand different breeds. although most sources do not recognize the marginal and sub-breeds included in larger counts. The Food and Agriculture Organization of the UN (FAO) listed 1229 breeds as of 2006.FAO. 2007. State of the world's animal genetic resources for food and agriculture Sheep are usually classified as being best suited to furnishing a certain product: wool, meat, milk, hides, or a combination. Other features used when classifying sheep include face color (generally white or black), tail length, presence or lack of horns, and the topography for which the breed has been developed. This last point is stressed in the UK, where breeds are described as either upland (hill or mountain) or lowland breeds. A sheep may also be of a fat-tailed type, with larger deposits of fat within and around its tail. In the wild, this fat tail could store nutrients, a useful trait in arid environments. In cultivation, they are generally dual-purpose sheep common in Africa and Asia.
Breeds are often categorized by the type of their wool. Fine wool breeds are those that have wool of great crimp and density, which are preferred for textiles. Most of these were derived from Merino sheep, and the breed continues to dominate the world sheep industry. Downs breeds have wool between the extremes, and are typically fast-growing meat and ram breeds with dark faces.D'Arcy, J.B., Sheep Management & Wool Technology, NSW University Press, 1986, Some major medium wool breeds, such as the Corriedale, are dual-purpose crosses of long and fine-wooled breeds and were created for high-production commercial flocks. Long wool breeds are the largest of sheep, with long wool and a slow rate of growth. Long wool sheep are valued for crossbreeding and have been used to create new, merged sheep types. For example, the American Columbia breed was developed by crossing Lincoln rams (a long wool breed) with fine-wooled Rambouillet ewes.