Sheep and goats are closely related (both are part of the Caprinae subfamily) and it can sometimes be difficult to tell them apart just by their appearance.
However, they are distinct species, so hybrids are rare and are always sterile. A sterile hybrid of a sheep and a goat is called a geep or shoat and has 57 chromosomes (sheep have 54 chromosomes, goats 60). It should not be confused with the chimeric gene obtained by fusing a goat embryo and a sheep embryo.
Visually, sheep and goats differ in the beard and upper lip, which is split in sheep and unique in goats. The tail of sheep, although short, hangs down while that of goats is erect. Sheep breeds are also often naturally hornless (either in both sexes and only in females), while naturally hornless goats are rare (although many goats are artificially deprived of their horns). Males of the two species differ in that goats have a characteristic strong odor during rutting, whereas rams do not.
The domestic sheep species are animals raised for multiple purposes. There are now over 200 sheep breeds created to serve these various purposes. Some authors have counted one or even several thousand races, but these numbers cannot be verified. Almost all the sheep types are classified according to the purpose for which they are best suited: wool, meat, milk, skin, or a combination of these for mixed breeds.
Other characteristics that are used to classify sheep are the colour of the face (usually white or black), length of the tail, the presence or absence of horns, the topography of the region where the breed has been developed. This last point is particularly noted in the United Kingdom, where the races are described as being highland or lowland breeds. Sheep can also be classified by whether there is fat in their tail. Fat-tailed sheep are rare in Europe, but common in Africa and Asia. These sheep are even subdivided into fat butted sheep and sheep with fat tail stricto sensu.
Breeds are also classified based on how well they are suited to produce a certain type of breeding stock. As a rule, sheep are classified as ewe breeds or ram breeds. Purebred ewes are those that are large framed and have good reproductive and mothering abilities. Their lambs are used to replace the lambs of other races. Ram breeds are bred for rapid growth and carcass quality and males are mated with ewes from other breeds that are bred to produce lambs for slaughter. The lowland and highland breeds are also treated this way. The highland large framed ewes are mated with larger and faster-growing lowland rams to give ewe lambs that will become breeding ewes called gimmers, which will be crossed with meat rams to produce quality lamb meat. Many breeds, especially the rare or primitive ones, do not fit into any of these categories.
Breeds are classified according to their type of wool. Wool breeds are those with dense, curly wool, which is very popular. Most of them come from Merino sheep whose breed continues to dominate the industrial world of wool. The record selling price for a sheep belongs to an Australian merino ram that was sold for $ 16,000. Mixed wool breeds are generally fast-growing meat breeds crossed with black-headed rams. Some large intermediate breeds, such as the Corriedale, bred for its meat and wool, are a crossbreed of long wool breeds with a fine wool root and were bred for large commercial production. Long-wool breeds are larger breeds but generally have a slower growth rate. Breeds with long wool are most popular for crossbreeding, to improve the attributes of other sheep types. For example, the American Columbia breed was developed by crossing Lincolns rams (a long wool breed) with fine wool Rambouillet merino sheep. A new British breed, the Exlana, resulting from the cross-breeding of a Blackbelly Barbados and a Sainte-Croix, was developed to automatically lose its wool as soon as temperatures rise. The wool having lost a lot of its value, this prevents the unprofitable shearing.
Some sheep types produce coarse, long, or medium-haired wool. These breeds are traditionally used to make carpet wool, wool of great variability, of which main quality is withstanding intensive use. As the demand for quality wool rugs decreases, some breeders of this type of sheep have tried to use some of these traditional breeds for other purposes. Others are still used primarily as a meat breed.
A small number of sheep breeds are used for milk. Most are mixed breeds, bred primarily for meat or wool, secondarily for milk, but there are a few breeds that are primarily used for milking. These sheep produce bigger quantities of milk over longer periods. The difference in milk quality is in the fat and protein content, but not in the lactose content. The duration of lactation varies from 90 to 150 days for domestic ewes and from 120 to 240 days for dairy breeds. Milk production is 50 to 100 liters per year for domestic ewes and 180 to 500 for the best dairy breeds. Some milk types are transformed into famous sheep cheese: Manchego in Spain, Roquefort in France, Feta in Greece.
Another group of sheep breeds is used for their fur because their hair does not curl like in other breeds. These sheep, which resemble the first domestic sheep before the development of woolen breeds, are bred for meat and skin. Some modern breeds of furry sheep, like the Dorper, are the result of cross-breeding of woolen breeds and furry breeds. These breeds are less expensive to maintain because they do not need to be shorn. Also, they are more resistant to external parasites and better withstand hot weather.
With the modern rise of industrial enterprises and the decline of family farms, many sheep breeds are at risk of extinction. The UK’s Rare Breeds Survival Trust has listed 25 breeds with only 3,000 animals and the American Livestock Breeds Conservancy has listed 14 breeds with less than 10,000. Preferences for breeds of uniform characteristics and fast growth have pushed traditional breeds away from factory sheep farming. The remaining traditional breeds owe their survival to the efforts of family farmers and species conservation organizations.