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. 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. are a medium wool, black-faced breed of meat sheep that make up 60% of the sheep population in the U.S. 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 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. Sheep have good hearing, and are sensitive to noise when being handled. 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,
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. Some sources give a count of a thousand or more breeds, but these numbers cannot be verified, according to some sources. 1314 breeds as of 1995 and 1229 breeds as of 2006. (These numbers exclude extinct breeds, which are also tallied by the FAO.) For the purpose of such tallies, the FAO definition of a breed is "either a subspecific group of domestic livestock with definable and identifiable external characteristics that enable it to be separated by visual appraisal from other similarly defined groups within the same species or a group for which geographical and/or cultural separation from phenotypically similar groups has led to acceptance of its separate identity." 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. 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. Coarse or carpet wool sheep are those with a medium to long length wool of characteristic coarseness. Breeds traditionally used for carpet wool show great variability, but the chief requirement is a wool that will not break down under heavy use (as would that of the finer breeds). As the demand for carpet-quality wool declines, some breeders of this type of sheep are attempting to use a few of these traditional breeds for alternative purposes. Others have always been primarily meat-class sheep. hair sheep in Mudgegonga, Victoria, Australia. This is a new breed of hair sheep suited for the hot and varied Australian climate. A minor class of sheep are the dairy breeds. Dual-purpose breeds that may primarily be meat or wool sheep are often used secondarily as milking animals, but there are a few breeds that are predominantly used for milking. These sheep produce a higher quantity of milk and have slightly longer lactation curves. In the quality of their milk, the fat and protein content percentages of dairy sheep vary from non-dairy breeds, but lactose content does not. A last group of sheep breeds is that of fur or hair sheep, which do not grow wool at all. Hair sheep are similar to the early domesticated sheep kept before woolly breeds were developed, and are raised for meat and pelts. Some modern breeds of hair sheep, such as the
Dorper, result from crosses between wool and hair breeds. For meat and hide producers, hair sheep are cheaper to keep, as they do not need shearing. Heritage or heirloom breeds have been pushed to the margins of the sheep industry. == Diet ==