About Ovis aries vignei Blyth, 1841
Domestic sheep are relatively small ruminants, typically with crimped hair called wool, and often have horns that form a lateral spiral. Compared to their wild relatives and ancestors, they are uniquely neotenic, a change brought about by human selective breeding. A small number of primitive sheep breeds keep some wild characteristics, such as short tails. Horn presence varies by breed: domestic sheep may be completely polled (hornless), have horns in both sexes, or have horns only in males. Most horned breeds have one pair of horns, but a few breeds may have multiple pairs. Another trait that sets domestic sheep apart from wild ovines is their wide range of color variation. Wild sheep are mostly different shades of brown, with very limited color variation within their species. Domestic sheep can be colored anywhere from pure white to dark chocolate brown, and may even be spotted or piebald. Sheep keepers sometimes add artificial painted smit marks in any pattern or color to sheep for individual identification. Selection for white fleeces that dye easily started early in sheep domestication, and because white wool is a dominant trait, it spread quickly. Even so, colored sheep still appear in many modern breeds, and can show up as a recessive trait in entirely white flocks. While white wool is preferred for large commercial markets, there is a small niche market for colored fleeces, mostly used for handspinning. Fleece texture varies widely between breeds, ranging from dense and heavily crimped to long and hairlike. Wool type and quality can vary even between members of the same flock, so wool classing is a required step in the commercial processing of wool fiber. Mature size in height and weight differs across sheep breeds. Growth rate and mature weight are heritable traits that are commonly selected for during breeding. Ewes usually weigh between 45 and 100 kilograms (100 and 220 lb), while rams weigh between 45 and 160 kilograms (100 and 350 lb). Sheep have 20 teeth once all their deciduous teeth have erupted, and mature sheep have 32 teeth. Like other ruminants, the lower front teeth bite against a hard, toothless pad on the upper jaw. This arrangement lets sheep pick off vegetation, which the rear teeth then grind before it is swallowed. Ruminants have eight lower front teeth, but there is disagreement over whether these are all eight incisors, or six incisors and two incisor-shaped canines. This gives sheep one of two possible dental formulas: either 0.0.3.3 / 4.0.3.3 or 0.0.3.3 / 3.1.3.3, with a large diastema between the front teeth and the molars. In a sheep's first few years of life, you can calculate its age from its front teeth: one pair of milk teeth is replaced by larger adult teeth each year, and the full set of eight adult front teeth is complete by around four years of age. As sheep get older, they gradually lose their front teeth, which makes feeding harder and harms the animal's health and productivity. Because of this, domestic sheep on regular pasture begin to decline slowly starting at four years of age. Sheep have a life expectancy of 10 to 12 years, though some sheep can live as long as 20 years. Sheep have good hearing, and are sensitive to noise when handled. They have horizontal slit-shaped pupils and excellent peripheral vision, with total visual fields of approximately 270° to 320°, allowing them to see behind themselves without turning their heads. Many breeds have only short hair on the face, and some breeds have any facial wool limited to the poll and the area around the mandibular angle, so the wide peripheral vision range applies to these breeds. A few breeds grow a lot of wool on the face; for some individuals of these breeds, peripheral vision can be greatly reduced by a condition called wool blindness, unless the wool around the face has been recently shorn. Sheep have poor depth perception, so shadows and dips in the ground can cause sheep to stop and refuse to move forward. In general, sheep tend to move out of dark areas into well-lit areas, and prefer to move uphill when disturbed. Sheep also have an excellent sense of smell, and like all species in their genus, they have scent glands just in front of the eyes and between the toes on their feet. The purpose of these glands is not confirmed, but the facial glands may be involved in breeding behaviors. The foot glands may also be related to reproduction, though other possible functions have been proposed, such as secreting waste product or leaving scent markers to help lost sheep rejoin their flock. Sheep follow a similar reproductive strategy to other herd animals. A group of ewes is generally mated by a single ram, which has either been selected by a breeder or, in feral populations, has established dominance through physical competition with other rams. Most sheep are seasonal breeders, though some can breed year-round. Ewes generally reach sexual maturity at six to eight months old, and rams generally reach sexual maturity at four to six months, though there are exceptions. For example, Finnsheep ewe lambs can reach puberty as early as 3 to 4 months, and Merino ewes sometimes reach puberty at 18 to 20 months. Ewes have estrus cycles approximately every 17 days; during estrus, they emit a scent and show physical displays toward rams to signal they are ready to mate. In feral sheep, rams fight during the rut to determine which individuals can mate with ewes. Rams, especially unfamiliar rams, will also fight outside the breeding period to establish dominance, and rams can kill one another if allowed to mix freely. Even normally friendly rams may become aggressive toward humans during the rut due to increased hormone levels. After mating, sheep have a gestation period of about five months, and normal labor takes one to three hours. While some breeds regularly produce larger litters of lambs, most give birth to single or twin lambs. During or soon after labor, ewes and lambs may be kept in small lambing jugs, small pens designed to make it easier to observe ewes carefully and help strengthen the bond between ewes and their lambs. Ovine obstetrics can be challenging. Over generations of selectively breeding ewes that produce multiple offspring with higher birth weights, sheep producers have accidentally caused some domestic sheep to have difficulty lambing; balancing easy lambing with high productivity is one of the ongoing dilemmas in sheep breeding. If problems occur, people present at lambing can help the ewe by extracting or repositioning lambs. After birth, ideally the ewe will break the amniotic sac if it has not broken during labor, and start licking the lamb clean. Most lambs begin standing within an hour of birth. In normal cases, lambs nurse after standing, receiving vital colostrum milk. Lambs that cannot nurse or are rejected by their ewe need help to survive, such as bottle-feeding or fostering by another ewe. Most lambs are born outdoors. When lambs are several weeks old, lamb marking is performed: this includes ear tagging, docking, mulesing, and castrating. Vaccinations are usually given at this time as well. Numbered ear tags are attached or ear marks are applied to make it easier to identify individual sheep later. Docking and castration are commonly done after 24 hours to avoid interfering with maternal bonding and the lamb's consumption of colostrum, and are often done no later than one week after birth to minimize pain, stress, recovery time, and complications. The first round of vaccinations, commonly against clostridial disease, is usually given when lambs are around 10 to 12 weeks old; this is when the concentration of maternal antibodies passively received via colostrum is expected to have dropped low enough to let lambs develop active immunity. Ewes are often revaccinated annually about three weeks before lambing, to provide high antibody concentrations in colostrum during the first several hours after lambing. Ram lambs that will either be slaughtered or separated from ewes before sexual maturity are not usually castrated. Animal rights groups have raised objections to all these procedures, but farmers defend them by stating they reduce costs and only inflict temporary pain. Sheep are the only mammal species besides humans that exhibit exclusive homosexual behavior. Around 10% of rams refuse to mate with ewes but will readily mate with other rams, and thirty percent of all rams show at least some homosexual behavior. Additionally, a small number of females that shared the uterus with a male fetus as fraternal twins are freemartins: they are behaviorally masculine and lack functioning ovaries. Sheep meat and milk were among the earliest staple protein sources consumed by human civilization after the shift from hunting and gathering to agriculture. Sheep meat prepared for food is called either mutton or lamb, and approximately 540 million sheep are slaughtered for meat each year worldwide. The word mutton comes from the Old French moton, the word for sheep used by Anglo-Norman rulers across much of the British Isles in the Middle Ages. This became the name for sheep meat in English, while the Old English word sceap was kept for the live animal. In modern usage, mutton refers to meat from mature sheep usually at least two years of age, while lamb refers to meat from immature sheep less than one year old. In the 21st century, the countries with the highest per capita sheep meat consumption are the Arab states of the Persian Gulf, New Zealand, Australia, Greece, Uruguay, the United Kingdom, and Ireland, where people eat 14–40 lbs (3–18 kg) of sheep meat per capita each year. Sheep meat is also popular in France, Africa (especially the Arab world), the Caribbean, the rest of the Middle East, India, and parts of China, a pattern that often reflects a long history of sheep production. In these countries in particular, dishes made with alternative cuts and offal are popular or traditional. Sheep testicles, called animelles or lamb fries, are considered a delicacy in many parts of the world. One of the most unusual sheep meat dishes is the Scottish haggis, made from various sheep innards cooked with oatmeal and chopped onions inside a sheep's stomach. In comparison, countries like the United States consume one pound or less (under 0.5 kg) of sheep meat per capita yearly; Americans eat 50 pounds (22 kg) of pork and 65 pounds (29 kg) of beef annually. In these countries, mutton is rarely eaten, and people tend to prefer the more expensive cuts of lamb, mostly lamb chops and leg of lamb. Though sheep's milk is rarely drunk fresh today, it is primarily used to make cheese and yogurt. Sheep only have two teats, and produce a much smaller volume of milk than cows. However, sheep's milk contains far more fat, solids, and minerals than cow's milk, which makes it ideal for cheese-making. It also resists contamination during cooling better because of its much higher calcium content. Well-known cheeses made from sheep milk include feta from Bulgaria and Greece, Roquefort from France, Manchego from Spain, and pecorino romano and ricotta from Italy (the Italian word for sheep is pecore, giving pecorino its name). Yogurts, especially some forms of strained yogurt, may also be made from sheep milk. Many of these products are now often made with cow's milk, especially when produced outside their country of origin. Sheep milk contains 4.8% lactose, which may affect people who are lactose intolerant. As with other domestic animals, the meat of uncastrated males is lower quality, especially as the animal matures. A bucky lamb is a lamb that was not castrated early enough, or was castrated improperly, leaving one testicle retained. These lambs are worth less on the market.
