Sheep

"Sheep" redirects here. For other uses, see Sheep (disambiguation).

Domestic sheep
A research flock at US Sheep Experiment Station near Dubois, Idaho
Conservation status
Domesticated
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	Bovidae
Subfamily:	Caprinae
Genus:	Ovis
Species:	O. aries
Binomial name
Ovis aries Linnaeus, 1758

Domestic sheep (Ovis aries) are quadrupedal, cloven-hoofed mammals kept as livestock. Though technically the term "sheep" applies to all Ovis species, in everyday use it typically refers to Ovis aries. Sheep are the most numerous of their genus, and are most likely descended from the wild mouflon. Sheep were one of the earliest animals domesticated for agricultural purposes; primarily for their valuable fleece and meat. A sheep's wool is the most widely used of any animal, and is typically harvested by shearing. Ovine meat is called "lamb" when from younger animals and "mutton" when from older ones. They continue to be vital livestock internationally, and are occasionally raised for pelts, as dairy animals, and as model organisms by science.

Sheep husbandry is practiced globally, and has played an important role in many economies throughout time, most notably Australia, New Zealand, Patagonian nations, and the United Kingdom in the modern era. Sheep raising has a large lexicon of unique terms which differ considerably by region. Use of the name "sheep" began in Middle English as a derivation of the Old English word scēap; it is both the singular and plural name for the animal. A group of sheep is called a flock, herd or mob. Adult female sheep are referred to as ewes, intact males as rams, castrated males as wethers, and younger sheep as lambs. Many other specified terms for the various life stages of sheep exist, generally related to lambing, shearing, and age.

Being a key animal in the history of farming, the sheep has a deeply entrenched place in human culture, and finds representation in much modern language and symbology. As livestock, sheep are most-often linked to 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. In contemporary English language usage, people who are timid, easily led, or stupid are often compared to sheep.

Description

Domestic sheep are ruminating bovids, typically with horns forming a lateral spiral and crimped hair called wool. Domestic sheep differ from their wild relatives and ancestors in several respects. Wild sheep have uncrimped hair and short tails. Some primitive breeds of domestic sheep have such tails, but a long tail—along with entirely white wool—seems to have been an early result of domestication. All wild sheep, male and female, have horns. Domestic sheep may have horns (usually two, but sometimes four or more) or be completely polled, depending on breed and gender.

Sheep have a rather wide range of height and weight, largely depending on breed. The rate of a sheep's growth and their eventual mature weight is a highly heritable trait that is often a point of focus for selective breeding. Ewes typically weigh between 100 and 225 pounds (45–100 kg), and rams (being generally larger than ewes) between 100 and 350 pounds (45–160 kg). Mature sheep have 32 teeth (dental formula: I:0/4 C:0/0 P:3/3 M:3/3). There are six molars and six premolars, all paired in the upper and lower jaws, together forming broad grinding surfaces at the back of the mouth. As in other ruminants, the eight incisors are all in the lower jaw, biting against a hard, toothless pad in the upper jaw; together these are used to pick off vegetation. There are no canines, but there is a large gap where they would be between the incisors and the premolars. Until the age of four (when all the adult teeth have erupted), it is possible to distinguish the age of sheep from their front teeth: a pair of incisors erupts each year. Though some sheep may live as long as 20 years, domestic sheep on normal pasture begin to decline slowly from four years on, the loss of teeth making it progressively harder for them to feed and thus hindering the health and productivity of the animal. The average life expectancy of a sheep is consequently 10 to 12 years.

A polled sheep's skull

Sheep have good hearing, and are sensitive to noise when being handled. Sheep have horizontal slit-shaped pupils, and possess a wide peripheral field of vision with some ability to distinguish color. With what is estimated to be approximately 270° to 320° of wide-angle vision, sheep can see behind themselves without turning their heads (though this ability may be impaired slightly by any wool present around the eyes). However, sheep have poor depth perception; shadows and dips in the ground may cause sheep to balk. In general, sheep have a tendency to want to move out of darkness and in to well-lit areas. Sheep have an excellent sense of smell, and—like all species of their genus—have scent glands located on their face just in front of the eyes, and interdigitally on the feet. The purpose of these glands is not known for certain, but those on the face are likely to be related to breeding behavior. The interdigital glands may also be related to sexual selection, but alternative reasons, such as secretion of a waste product or a scent marker to help lost sheep find their flock, have also been posited.

Sheep and goats are closely related (both are in the subfamily Caprinae), and it can sometimes be difficult to differentiate them by appearance alone. However, the genes of sheep and goats differ so greatly that cross-species hybrids rarely occur, and are always infertile. A hybrid of a ewe and a buck (a male goat) is called a sheep-goat hybrid, and is not to be confused with the genetic chimera called a geep. Visual clues to differentiating sheep and goats include the beard and divided upper lip of goats, which sheep do not have. Sheep tails also hang down, even when short or docked, while the tails of goats are held upwards. Sheep breeds are also 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 especially in that buck goats acquire a unique and very strong odor during the rut, whereas rams do not.

A Scottish Blackface ram (left) and ewe (right). Scottish Blackface are a horned, dark-faced breed.

Breeds

See also: List of sheep breeds

The domestic sheep is a multi-purpose animal, and the more than 200 breeds now in existence were created to serve these diverse purposes. Some sources give a count of a thousand or more breeds, but concrete documentation has not been produced for such a number. Sheep almost all are classified as being best suited to furnishing a certain product: wool, meat, milk, hides or a combination thereof (i.e. dual-purpose breeds). Other distinctions made in classifying sheep include face color (generally white or black), the presence or lack of horns, and the topography of a breed's origin. This last point is especially stressed in the United Kingdom, where breeds are described as either upland (a.k.a. hill or mountain) or lowland (a.k.a. down) breeds, each traditionally are said to bear characteristics imparted from their respective terrain. Especially in Africa and Asia, a sheep may be of a fat-tailed breed, which is a type of meat or dual-purpose sheep with larger deposits of fat within its tail.

Ovine breeds are also grouped based on how well they are suited to producing a certain type of breeding stock. Generally, sheep are thought to be either "ewe breeds" or "ram breeds". Ewe breeds are those that have good reproductive and mothering capabilities, and are for replacing ewes in standing flocks. Ram breeds are selected for rate of weight gain and carcass quality, and are mated with ewe breeds to produce market lambs. Many breeds, especially rare or primitive ones, fall into neither category strictly. Lowland and upland breeds are also crossed in this fashion, with the hardy hill ewes crossed with larger, fast-growing lowland rams to produce a type of ewe called a mule, which can then be crossed with meat-type rams to produce prime market lambs.

The Soay breed, as with this ewe, is closest in general appearance to the Mouflon ancestors of sheep.

Sheep breeds are categorized by the type of wool they exhibit, irrespective of whether they are favored for meat or wool production. Fine wool breeds are those that have wool of great crimp and density, and are consequently preferred by the textile industry. Most of these breeds were derived from Merino sheep. Medium wool breeds have wool between the extremes, and are typically fast-growing meat and ram breeds with dark faces. Some major medium wool breeds, such as the Corriedale, are dual-purpose crosses of long and fine-wooled breeds created for high-production commercial flocks. Long wool breeds are the largest of sheep, with lengthy wool and a slow rate of maturation. Long wool sheep are most valued by modern agriculture for crossbreeding to improve the attributes of other sheep types. For example: the American Columbia breed was developed through 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 more variability in general traits than other types, the chief requirement being 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 reposition a few of the traditional breeds to alternative purposes. Others have always been primarily meat–class sheep.

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 very early type of domesticated sheep kept before wooly breeds were developed, and are raised for meat and pelts. Some modern breeds of hair sheep, such as the Dorper, are the result of crosses between wooled and hair breeds. Resistant to parasites and needing no shearing, hair-class sheep are increasing in popularity among sheepmeat producers.

Diet

Anatomy of the sheep's ruminant system: 1. Atrium ruminis 2. Saccus dorsalis 3. Saccus ventralis 4. Recessus ruminis 5. Saccus cecus caudodorsalis 6. Saccus cecus caudoventralis 7. Sulcus cranialis 8. Sulcus longitudinalis sinister 9. Sulcus coronarius dorsalis 10. Sulcus coronarius ventralis 11. Sulcus caudalis 12. Sulcus accessorius sinister 13. Insula ruminis 14. Sulcus ruminoreticularis 15. Reticulum 16. Abomasum 17. Esophagus 18. Spleen.

Sheep are exclusively herbivorous mammals. Like all ruminants, sheep have a complex digestive system composed of four stomachs that allows them to break down otherwise inedible roughage such as stems, leaves, and seed hulls in to complex carbohydrates. Sheep follow a diurnal pattern of activity, beginning to feed at dawn and throughout the day until dusk, stopping sporadically to rest and chew their cud. Ideal pasture for sheep is not lawn-like grass, but an array of grasses, legumes and forbs. Types of land where sheep are raised vary widely, from pastures that are seeded and improved intentionally to rough, native lands. Common plants toxic to sheep are present in most of the world, and include (but are not limited to) acorns, yew, and all plants of the Rosaceae, nightshade, rhododendron, and milkweed families. Sheep also may perish from consuming man-made substances. Sheep are unlike goats and deer, which are browsing animals that prefer weeds and taller foliage. With a much narrower face, it can crop plants very close to the ground and can overgraze a pasture much faster than cattle. For this reason, most shepherds advocate some type of managed grazing whereby a flock is rotated through multiple pastures, giving plants time to recover. Other than forage, the only other common staple feed for sheep is hay, generally during the winter months. The ability to survive solely on pasture (even without hay) varies with breed, but all sheep are capable of doing so. Also included in most sheep's diets are minerals, either in a trace mix or in licks.

Naturally, a constant source of potable water is also a fundamental requirement for sheep. The amount of water needed by sheep fluctuates with the season and the type and quality of the food they consume. When sheep feed on large amounts of new growth and there is precipitation (including dew, as sheep are dawn feeders), sheep need less water. When sheep are confined or are eating large amounts of cured hay, more water is typically needed. Sheep also require clean water, and may refuse to drink water that is covered in scum or algae.

Sheep are one of the few livestock animals raised for meat today that have never been widely kept in an intensive, confined animal feeding operation. Though there is a growing movement advocating extensive, free range farming, the vast majority of cattle, pigs, and poultry are still produced at factory farms. In contrast, only a few specific categories of sheep are regularly given high-concentration grain feed. Many sheep breeders choose to "flush" ewes and rams during breeding, providing feed in key periods to increase fertility and birth weight. As 70% of a lamb's growth occurs in the last five to six weeks of gestation, ewes are also flushed during that period. Other than flushing, only nursing ewes, lambs and especially old, infirm sheep are commonly provided with supplemental grain. Feed provided to sheep must be of a kind specially formulated for them, as most cattle, poultry, pig, and even some goat feeds contain amounts of copper that are lethal to sheep. The same danger applies to mineral supplements such as salt licks. When changing a sheep's content or time of feeding, changes are generally made gradually so as not to disrupt the function of the rumen; sudden changes in a sheep's diet can cause potentially fatal conditions such as bloat.

Behavior

Sheep being herded through the streets of Cologne

Sheep are prey animals with a strong gregarious instinct, and a majority of sheep behavior can be defined in these terms. When sheep gather in larger social groups, it allows some sheep to concentrate on feeding and social interaction while others keep watch for a threat. All sheep exhibit some degree of natural flocking behavior, varying with breed. The social nature of sheep is exploited by farmers, who can use a strong flocking instinct to keep sheep together on open pastures and to move them more easily. Shepherds may also use sheepdogs in this effort, whose inbred herding ability can assist in moving flocks. In regions such as Iceland, where sheep have no natural predators, none of the native breeds of sheep exhibit a strong flocking behavior. Sheep without a flocking instinct tend to scatter rather than stay together when threatened, in a similar manner to goats. It is virtually impossible to use herding dogs with such breeds. Sheep can also become hefted to one particular pasture so they do not roam. This is in particular a characteristic of English upland breeds. Ewes teach this behavior to their lambs, and if flocks are culled entirely it must be retaught to them.

Lambs tussle during play. Lambs also often imitate adult sheep behaviors.

Flock dynamics in sheep are as a rule only exhibited in a group of four or more sheep. Fewer sheep may not react as normally expected when alone or with very few other sheep. This is one reason why three is the minimum number of sheep in a sheepdog trial; it places the greatest pressure on a dog's herding abilities. For sheep, the primary defense mechanism is simply to flee from danger when their flight zone is crossed. Secondarily, cornered sheep may attempt to leap at and ram threats in order to escape. This is particularly true for ewes with newborn lambs and rams (hence the verb form of the word ram). In displaying flocking, sheep have a strong lead-follow tendency, and a leader often as not is simply the first sheep to move. However, sheep do establish a pecking order through physical displays of dominance. Dominant animals are inclined to be more aggressive with other sheep, and usually feed first at troughs. Relationships in flocks tend to be closest among related sheep: in mixed-breed flocks same-breed subgroups tend to form, and a ewe and her direct descendants often move as a unit within very large flocks.

Sheep are frequently thought of as extremely stupid animals. A sheep's herd mentality and quickness to flee and panic in the face of stress often make shepherding a difficult endeavor for the uninitiated. Despite these perceptions, a University of Illinois monograph on sheep found them to be just below pigs and on par with cattle in IQ, and some sheep have shown problem-solving abilities; a flock in Yorkshire, England found a way to get over cattle grids by rolling on their backs. If worked with patiently sheep may learn their names, and many sheep are trained to be led by halter for showing and other purposes. Very rarely, sheep are used as pack animals. Tibetan nomads distribute baggage equally throughout a flock as it is herded between living sites.

Reproduction

A horned ram

Sheep follow a similar reproductive strategy to other herd animals. A flock of ewes is generally mated by a single ram, who has either been chosen by a farmer or has established its dominance through physical contest with other rams (in feral populations). Most sheep are seasonal breeders, though some are able to breed (also called tupping) year-round. Ewes generally reach sexual maturity at six to eight months of age, and rams generally at four to six (ram lambs have occasionally been known to impregnate their mothers at two months). Ewes enter in to estrus cycles about every 17 days, lasting for approximately 30 hours. In addition to emitting a scent, they indicate their readiness through physical displays towards rams. Sheep may alternatively display a preference for homosexuality, and the behavior occurs in about eight percent of rams on average. Its occurrence does not seem to be related to dominance or flock hierarchy, rather the ram's typical motor pattern for intercourse is merely directed at rams instead of ewes. Without human intervention, rams fight during the rut to determine which individuals may mate with ewes. Rams, especially unfamiliar ones, will also fight outside the breeding period to establish dominance; rams can kill one another if allowed to mix freely. During the rut, even normally friendly rams may become dangerous to humans due to increased hormone levels. Historically, especially aggressive rams were sometimes blindfolded or hobbled when interaction with people was necessary. Today, those who keep rams typically prefer softer preventative measures, such as moving within a clear line to an exit, never turning their back on a ram, and possibly using dousing with water or a diluted solution of bleach or vinegar to dissuade charges.

Without ultrasound or other special tools, ascertaining whether sheep are in fact pregnant is initially difficult. Ewes only begin to visibly show a pregnancy about six weeks before the birth, so shepherds sometimes merely rely on the assumption that a ram has been given enough time to impregnate all the ewes. However, a very commonly used piece of equipment for discerning which ewes have been mated with is a marking harness. By fitting a ram with a chest harness that holds a special crayon, ewes that have been mounted are marked with its color. Dye may also simply be directly applied to the ram's brisket. After mating, sheep have a gestation period of around five months. Within a few days of the impending birth, ewes begin to behave differently. They may lay down and stand erractically, paw the ground, or otherwise act out of sync with normal flock patterns. A ewe's udder will quickly fill out, and her vulva will swell. Uterine or anal prolapse may also occur in problem cases, in which a physical retainer used to hold the orifice in is utilized. When birth is imminent, contractions begin to take place, and the fitful behavior of the ewe may increase. A normal labor may take one to several hours: depending on how many lambs are present, the age of the ewe, and her physical and nutritional condition prior to the birth. Though some breeds may regularly throw larger litters of lambs, most produce either single or twin lambs. At some point, usually either at the beginning of labor or just after the births have occurred, ewes and lambs are confined to small lambing jugs. These pens, which are generally two to eight feet in length and width, are designed to facilitate both careful observation of ewes and to cement the bond between them and their lambs.

The second of twins being born on a New Zealand pasture

For shepherds, ovine obstetrics is sometimes a problematic phenomenon. While the majority of births are relatively normal and do not require any assistance, there are a large number of possible complications that may arise. A lamb may present in the normal fashion (with both legs and head forward), but may simply be too large to slide out of the birth canal. This often happens when large rams are crossed with diminutive ewes (this is related to breed; rams are naturally larger than ewes by comparison). Lambs may also present themselves forward, with one shoulder to the side, completely backward, or with only some of their limbs protruding. Lambs may also be stillborn. In the case of any such problems, those present at lambing (who may or may not include a veterinarian, most shepherds become accomplished at lambing to some degree) may assist the ewe in extracting or repositioning lambs. After the birth, ewes ideally break the amniotic sac (if it is not broken during labor), and begin licking clean the lamb. The licking both clears the nose and mouth, dries the lamb, and stimulates it. Lambs that are breathing and healthy at this point begin trying to stand, and ideally do so between an half and full hour, with help from the mother. Generally after lambs stand, the umbilical cord is trimmed to about an inch (2.54 centimeters). Once trimmed, a small container (such as a film canister) of iodine is held against the lamb's belly over the remainder of the cord to prevent infection.

In normal situations, lambs nurse after standing, receiving vital colostrum milk. Lambs that either fail to nurse or are prevented from doing so by the ewe require aid in order to live. If coaxing the pair to accept nursing does not work, one of several steps may then be taken. Ewes may be held or tied to force them to accept a nursing lamb. If a lamb is not eating, a stomach tube may also be used to force feed the lamb in order to save its life. In the case of a permanently rejected lamb, a shepherd may then attempt to graft an orphaned lamb onto another ewe. Lambs are also sometimes grafted after the death of their mother, either from the birth or other event. Scent plays a large factor in ewes recognizing their lambs, so disrupting the scent of a newborn lamb with washing or over-handling may cause a ewe to reject theirs. Conversely, various methods of imparting the scent of a ewe's own lamb to an orphaned one may be useful in grafting. If an orphaned lamb cannot be grafted, then it usually becomes what is known as a bottle lamb: a lamb raised by people and fed via bottle.

An Oxford Down ewe and her twins in a lambing jug, note the iodine stains on the lambs

After lambs are stabilized, lamb marking—the process of ear tagging, docking, and castrating—is carried out. Vaccinations are usually carried out at this point as well. Ear tags with numbers are the primary mode of identification when sheep are not named; it is also the legal manner of animal identification in the European Union. When performed at an early age, ear tagging seems to cause little or no discomfort to lambs. However, using tags improperly or using tags not designed for sheep may cause discomfort, largely due to excess weight of tags for other animals. Castration is performed on ram lambs not intended for breeding, though some shepherds choose to avoid the procedure for ethical, economic or practical reasons. Docking, which is a shortening—not a complete removal—of sheep's tails is practiced for health reasons. The tail is removed just below the lamb's caudal tail flaps. Though docking is often considered cruel and unnatural by animal rights activists, it is considered by sheep producers large and small alike to be a critical step in maintaining the health of sheep. With long, wooly tails, sheep are extremely susceptible to parasites, especially those that cause flystrike. In Chuck Wooster's Living with Sheep, the author anecdotally relates his shearer's response when told of his opposition to docking: "There's nothing natural about a sheep walking around with a dozen pounds of wool on it, and nothing natural about a sheep with a wooly tail [here referring to the hairless tails of wild and primitive sheep]. Natural's got nothing to do with it. Unless you want to watch your lambs walking around with tails covered covered by maggots and flies, cut the tails off." Both castrating and docking can be performed with several different instruments. An elastrator places a tight band of rubber around an area, causing it to atrophy and fall off in a number of weeks. This process is bloodless and does not seem to cause extended suffering to lambs, who tend to ignore it after several hours. In addition to the elastrator, a Burdizzo, emasculator or knife are sometimes used. After one to three days in the lambing jugs, ewes and lambs are usually sufficiently stabilized to allow reintroduction to the rest of the flock.

Health

Sheep may fall victim to chemical, pathogenic and physical means of sickness and injury. As a prey species, a sheep's system is designed to hide the obvious signs of illness as much as possible, in order to prevent being targeted by predators. However, there are some signs of ill health that can be ascertained without any special testing. Sick sheep may be unwilling to eat, vocalize excessively, and be generally listless. Throughout history, much of the money and labor of sheep husbandry has gone in to dealing with sheep ailments in order to avoid the heavy losses sustained from them. Shepherds in history often created remedies through experimentation on the farm. In some countries, sheep do not have the economic impact to necessitate clinical studies designed to approve drugs specifically for usage with sheep. In such instance, many shepherds resort to extralabel usage of drugs approved for other animals. In the 21st century, a minority of sheep owners have turned to alternative treatments such as homeopathy, herbalism and even Traditional Chinese medicine to treat sheep veterinary problems. Though often met with skepticism, a few alternative treatments have been shown to be effective in trials for some specific problems.

Many breeders take a variety of preventative measures to ward off problems before they arrive. The first is to ensure that all sheep purchased for the initial flock and replacement animals are healthy to begin with. Many buyers avoid outlets (such as sale barns) which are known to be clearing houses for animals culled from healthy flocks as either sick or simply inferior. This can also mean maintaining a closed flock, and quarantining new sheep for a month. Two fundamental preventative programs are maintaining good nutrition and stressing sheep as little as possible. Handling sheep in loud, erratic ways causes them to emit cortisol, a stress hormone. Elevated amounts of cortisol can lead to a weakened immune system, thus making sheep far more vulnerable to disease. Signs of stress in sheep include: excessive panting, teeth grinding, restless movement, wool eating, and wood chewing. Preventing the presence of harmful chemical agents is also an important part of a sheep owner's work. Common culprits of poisoning include pesticide sprays, inorganic fertilizer, motor oil, as well as radiator coolant (the ethylene glycol antifreeze in this is sweet-tasting).

A common form of preventative medication for sheep are vaccinations and treatments for parasites. Both external and internal parasites are the most prevalent malady in sheep, and their susceptibility to them is a primary impediment to certified organic sheep farming. Various worms comprise most of the internal parasites, which are ingested during grazing, incubate within the sheep, and are expelled through the digestive system (beginning the cycle again). Oral parasite medicines known as drenches are given to a flock to treat worms, sometimes after a count of eggs in the sheep's feces has been taken to assess infestation levels. Afterwards, sheep may be moved to a new pasture to prevent ingesting the same parasites. External sheep parasites include: lice (for different parts of the body), sheep keds, nose bots, sheep itch mite, and maggots. Keds are blood-sucking parasites that can cause general malnutrition and decreased productivity, but are not fatal. Maggots are those of the bot fly and the blowfly. Fly maggots cause the extremely destructive condition of flystrike. Flies lay their eggs in wounds or wet, manure-soiled wool, and when the maggots hatch they burrow in to a sheep's living flesh, eventually resulting in death if unchecked. In addition to other treatments, crutching (shearing wool from a sheep's rump) is a common preventative method. Nose bots are flies that inhabit a sheep's sinuses, causing breathing difficulties and discomfort. Common signs are a discharge from the nasal passage, sneezing, and frantic movement such as head shaking. External parasites may be controlled through the use of backliners, sprays or immersive treatments (sheep dips).

A wide array of diseases caused by bacteria affect sheep, but a few are especially prevalent and some may even be transmittable to humans. Diseases of the hoof, such as foot rot and foot scald may occur, and are treated with footbaths and other remedies. These painful conditions cause lameness and retard a sheep's ability to feed. Ovine Johne's Disease is a wasting disease that affects young sheep. Blue tongue disease is an insect-borne illness causing fever and inflammation of the mucous membranes. Soremouth (also known as scabby mouth, contagious ecthyma or orf) is a skin disease leaving lesions that can be transmitted to persons handling infected flocks. More seriously, the organisms that can cause spontaneous enzootic abortion in sheep are easily transmitted to pregnant women. Also of concern are scrapie and foot and mouth disease, as both can decimate entire flocks. The latter poses a significant risk to humans. During the 2001 outbreak of foot and mouth disease, hundreds of sheep in the U.K. were culled, and some rare British breeds were at risk for extinction from the pandemic.

Predation

Other than parasites and disease, predation is a threat to sheep health and thereby the profitability of sheep raising. Sheep have very little ability to defend themselves, even when compared with other prey species kept as livestock. Even if sheep are not directly bitten or survive an attack, they may die from panic or from injuries sustained. However, the impact of predation varies dramatically with region. In Africa, Australia, the Americas, and parts of Europe and Asia predators can be a serious problem. In contrast, some nations are virtually devoid of sheep predators. Many islands that are known for extensive sheep husbandry are suitable largely because of their predator-free status. Worldwide, canids—including the domestic dog—are responsible for the majority of sheep deaths.

According to the National Agricultural Statistics Service, 224,200 sheep were killed in the U.S. by predators in 2004, comprising approximately 37% of all ovine deaths for that year. The sheep lost in that year represented a sum total of 18.3 million dollars for sheep producers. As all NASS statistics on sheep only take into account sheep after docking, the American Sheep Industry Association estimates that an additional 50-60,000 lambs were killed before docking occurred. Coyotes were responsible for 60.5% of all deaths, with the next largest being domestic dogs at 13.3%. Other North American predators of sheep included cougars (5.7%), bobcats (4.9%), eagles (2.8%), bears (3.8%), and foxes (1.9%). Wolves, ravens, vultures, and other animals together made up the remaining 7.1% of deaths.

In South America, the only widespread potential predators of sheep are cougars and jaguars, both of which are known to prey on livestock regularly. South American canids such as the Maned wolf and foxes of the genus Pseudalopex are also blamed for sheep deaths, but no evidence for a statistically significant amount of predation by these species has ever been presented. Though large, the South African sheep industry is significantly hindered by the innumerable predators present in the country. Other African nations that rely on sheep face a similar problem.

The main Australian predator of sheep is the dingo, which is a large-enough danger to sheep to precipitate the construction of the world's largest fence: the Dingo Fence. In contrast, New Zealand has no large carnivores whatsoever. The sole animal known to attack sheep in New Zealand is the rare, unusual kea parrot endemic to the country's South Island. The U.K. and Ireland once both had wolves and bears, but today only the Red fox and birds of prey remain a tangible threat to sheep in the British Isles.

History

Main article: History of agriculture

A Egyptian Criosphinx at Luxor

Sheep were among the first animals to be domesticated by mankind, with sources providing a domestication date between nine and eleven thousand years ago in Mesopotamia. Determining the exact genetic ancestry of domestic sheep is a complex problem, and no particular lineage has received complete acceptance in the scientific community. The most common theory currently supported by DNA analysis indicates that Ovis aries is jointly descended from both the European (O. musimon) and Asiatic (O. orientalis) species of mouflon. It has also been proposed that the European mouflon is an ancient breed of domestic sheep turned feral rather than an ancestor, the lack of a fossil record for the species may support this hypothesis. The urial (O. vignei) was once often thought to have been a forebear of domestic sheep; they occasionally interbreed with mouflon in the Iranian part of their range. However, both the urial, argali (O. ammon), and snow sheep (O. nivicola) possess a different number of chromosomes than other Ovis species, making any direct influence highly implausible. Contemporary evaluations of sheep DNA show no evidence of urial ancestry. Further DNA analysis comparing European and Asian breeds of sheep shows a significant percentage of genetic variance between the two. Two explanations for this phenomenon have been posited. The first is that there is a currently unknown species or subspecies of wild sheep that contributed to the formation of domestic sheep. A second theory suggests that this variation is the result of multiple waves of capture from wild mouflon, similar to the known development of other livestock.

Initially, sheep were kept solely for meat, milk and skins. Archaeological evidence from statuary found at sites in Iran suggests that selection for wooly sheep may have began circa 6000 BC, but the earliest woven wool garments have only been dated to two to three thousand years later. By that span of the Bronze Age, sheep with all the major features of modern breeds were widespread throughout Western Asia. However, one chief difference between ancient sheep and most modern breeds is the technique by which wool could be collected. Primitive sheep cannot be shorn, and must have their wool plucked out by hand in a process called '"rooing". This is due to the fact that their kemps (coarse, unworkable hairs) are still longer than the soft fleece. The fleece may also be collected from the field after it falls out. This trait survives today in unrefined breeds such as the Soay. The Soay, along with other Northern European breeds with short tails, unshearable fleece, diminutive size, and horns in both sexes, are more closely related to ancient sheep than most breeds found today. Originally, weaving and spinning wool was a handicraft practiced at home, rather than an industry. Egyptians, Babylonians, Sumerians, and Persians all depended on sheep; and though linen was the first fabric to be fashioned in to clothing, wool was a prized product. The raising of flocks for their fleece was one of the earliest industries, and flocks were a medium of exchange in barter economies. Numerous Biblical figures kept large flocks, and subjects of the king of Israel were taxed according to the number of rams they owned.

In Europe

See also: British Agricultural Revolution

A 1st Century CE relief of a bull, a sheep and a pig being led to sacrifice in Rome

From Southwest Asia, sheep husbandry spread quickly in to Europe. Practically from its inception, ancient Greek civilization relied on sheep as primary livestock, and were even said to name individual animals. Scandanavian sheep of a type seen today—with short tails and multi-colored fleece—were also present early on. Later, the Roman Empire kept sheep on a wide scale, and the Romans were an important agent in the spread of sheep raising throughout the continent. Pliny the Elder, in his Natural History (Naturalis Historia), speaks at length about sheep and wool. Declaring "Many thanks, too, do we owe to the sheep, both for appeasing the gods, and for giving us the use of its fleece.", he goes on to detail the breeds of ancient sheep and the many colors, lengths and qualities of wool. Romans also pioneered the practice of blanketing sheep, in which a fitted coat (today usually of nylon) is placed over the sheep to improve the cleanliness and luster of its wool.

During the Roman occupation of the British Isles, a large wool processing factory was established in Winchester, England circa 50 AD. By 1000 AD, England and Spain were recognized as the epicenters of sheep production in the Western world, and the word "sheep" itself was first used in Middle English, the language of the period. Etymologically the word is derived from the Old English term scēap, and it is akin to the Old High German scāf. As the progenitors of the extremely fine-wooled Merino breeds, the Spanish gained great wealth; wool money largely financed Spanish rulers, and thus, the voyages to the New World. The powerful Mestas controlled sheep production, and flocks had a lawful right of way for their migratory routes from Extremadura and Andalusia to Castile. Exportation of Merinos was a punishable offense that required royal permission, thus ensuring a near-absolute monopoly on the breed until Napoleon's invasion of that country in the mid-18th century. After the breaking of the export ban, fine wool sheep began to be distributed worldwide. For example, the export to Rambouillet by Louis XVI in 1786 formed the basis for the modern Rambouillet (or French Merino) breed.

A depiction of a ram from the Aberdeen Bestiary, a 12th century illuminated manuscript

The sheep industry in Spain was an instance of completely open range flock management, with enormous flocks of only a few breeds ranging over the entire nation. However, the ovine model used in England was quite different, and had a similar importance to economy of the British Empire; to this day the Lord Speaker of the House of Lords sits on a bench known as the Woolsack. The high concentration and more sedentary nature of shepherding in the U.K. allowed sheep especially adapted to their particular purpose and region to be raised, thereby giving rise to an exceptional variety of breeds in relation to the land mass of the country. This greater variety of breeds also produced a valuable variety of products to compete with the superfine wool of Spanish sheep. The growth of the sheep industry in Britain quickened in the 15th and 16th centuries due to booming wool prices and the greater pasture available due to a diminished population (the result of the Black Death). More landholders were willing and able to turn their lands over to pasture for sheep, and an influx of Flemish immigrants skilled in cloth making and dyeing during the reign of Edward III helped to cement the wool trade. By this time, Britain began moving from an open field system to one of enclosure. The unilateral closing of commons by landed gentry had enormously detrimental effects on local communities—entire villages were sometimes depopulated to make way for pasture—and was widely protested. By the time of Elizabeth I's rule, sheep and wool trade was the primary source of tax revenue to the Crown of England. An important event not only in the history of domestic sheep, but of all livestock, was the work of Robert Bakewell in the 1700s. Before his time, breeding for desirable traits was often based on chance, with no scientific process for selection of breeding stock. Bakewell established the principles of selective breeding—especially line breeding—in his work with sheep, horses and cattle, and his theories were an influence on the subsequent work of Gregor Mendel and Charles Darwin. His most important contribution to sheep was the development of the Leicester Longwool, a quick-maturing breed of blocky conformation that formed the basis for many vital modern breeds. Today, the sheep industry in Spain and the U.K. does not play as large an international role, even if it is often of local economic and cultural importance; both countries are still large consumers of sheep meat.

In the Americas

See also: Agricultural history of the United States

Corriedale lambs on Tierra del Fuego

No ovine species native to the Americas has ever been domesticated, despite being closer genetically to domestic sheep than many Asian and European species, having the same number of chromosomes. The first domestic sheep—most likely of the Churra breed—arrived with Christopher Columbus' second voyage in 1493. The next Transatlantic shipment to arrive was with Hernán Cortés in 1519, landing in Mexico. Neither of these established a substantial population of sheep, and no export of wool or animals is known to have occurred. The next transport of sheep to North America was not until 1607 with the voyage of the HMS Susan Conant to Virginia. However, the sheep that arrived in that year were all consumed because of a famine, and a permanent flock was not to reach the colony until two years later in 1609. Two decades later, the colonists had grown their flock to a total of 400. Sheep were also eventually purchased from the Dutch colonizers of Manhattan. In 1662, a woolen mill was built in Watertown, Massachusetts, and by the 1640s there were approximately 100,000 head of sheep in the 13 colonies. Early on, the British government banned further export of sheep to the Americas, or wool from it, in an attempt to stifle any threat to the wool trade in the British Isles. One of many restrictive trade measures that precipitated the American Revolution, the sheep industry in the Northeast grew despite the bans.

Gradually throughout the 1900s, sheep production moved westward, and today the vast majority of flocks reside on Western range lands. During this westward migration of the industry, competition between sheep and cattle operations grew more heated, eventually erupting in to range wars. Other than simple competition for grazing and water rights, cattlemen believed that the secretions of the foot glands of sheep made cattle unwilling to graze on places where sheep had stepped. Another effect of the westward movement of sheep flocks in North America was the decline of wild species such as Bighorn sheep (O. canadesis). Most diseases of domestic sheep are transmittable to wild ovines, and such diseases, along with overgrazing and habitat loss, are named as primary factors in the plummeting numbers of wild sheep. Sheep production peaked in the United States during 1940s and 50s at more than 55 million head. Henceforth and continuing today, the number of sheep in North America has steadily declined with wool prices and the lessening American demand for sheep meat.

In South America, especially in Argentina, Chile, Brazil, Uruguay, and Peru, there is an active modern sheep industry. Sheep keeping was largely introduced through immigration to the continent by Spanish and British peoples, for whom sheep were a major industry during the period. South America today has a large number of sheep, but the highest-producing nation (Brazil) kept only just over 15 million head in 2004, far less than most centers of sheep husbandry. Brazil is, however, not an export nation of any consequence in the sheep industry and sheep operations often find themselves in stiff competition from the immense cattle industry in the country. The most influential region internationally is that of Patagonia, and Patagonian shepherds are often employed by U.S. sheep producers. With few predators and almost no grazing competition (the only large native grazing mammal is the guanaco), the region is prime land for sheep raising. The most exceptional area of production is surrounding the La Plata river in the Pampas region. Sheep production in Patagonia peaked in 1952 at more than 21 million head, but has steadily fallen to less then ten today. Most operations focus on wool production for export from Merino and Corriedale sheep; the economic sustainability of wool flocks has fallen with the drop in prices, while the cattle industry continues to grow.

A champion Merino ram from the 1905 Sydney sheep show; Merinos with such extreme amounts of skin wrinkling on the body are no longer common

In Australia and New Zealand

Main article: Agriculture in Australia

Australia and New Zealand are crucial players in the contemporary sheep industry, and sheep are an iconic part of both countries' culture and economy. New Zealand has the highest density of sheep per capita (sheep outnumber the human population 12–1), and Australia is the world's indisputably largest exporter of sheep and cattle. Though sheep were present in these countries from the earliest stages of their colonization, the Merino breed—the cornerstone of the Australian sheep industry—was not introduced until 1789. While much of the growth in both nations was due to the active support of Britain, both worked to develop many unique new high-production breeds: the Corriedale, Coopworth, Perendale, Polwarth and most of the ten varieties of Merino were created in New Zealand or Australia. Wool production was a fitting industry for colonies far from their home nations. Before the advent of fast air and maritime shipping, wool was one of the few viable products that was not subject to spoiling on the long passage back to British ports. Flocks in Australia have always been largely range bands on fenced land, and are aimed at production of superfine wool for clothing and other products as well as meat. New Zealand flocks are kept in a fashion similar to English ones, in fenced holdings without herders. Though wool was once the primary income source for New Zealand sheep owners, today it has shifted to meat production.

Somewhat unusually for livestock, the Australian sheep industry is the only sector internationally to receive strident, widespread criticism for its practices. The custom of mulesing, in which skin is cut away from an animal's perineal area without anesthesia to prevent cases of flystrike, has been condemned widely as painful and unnecessary. In response, a program of phasing out mulesing is currently being implemented.Most of the sheep meat exported from Australia are either frozen carcasses to the U.K. or live animals to the Middle East. Shipped on converted oil tankers in what has been called crowded, unsafe conditions by critics, live sheep are desired by Middle Eastern nations to meet the requirements ritual halal slaughter. Opponents of the export—such as PETA—say that sheep exported to countries outside the jurisdiction of Australia's animal cruelty laws are treated with horrendous brutality and that halal facilities exist within Australia to make export of live animals redundant. A few celebrities and companies have pledged to boycott all Australian sheep products in protest.

Cultural significance

See also: List of fictional sheep

the global distribution of sheep circa 2004

Sheep have had a strong presence within many cultures, especially in areas where they form the most common type of livestock. A wide symbology relates to sheep in art, religion and language. The raising of sheep for wool and meat became a major industry in the U.K. Australia and New Zealand and remains significant. As a result, sheep and sheep shearing have become an important part of the cultural traditions of these countries in particular. More ancient references to sheep usually revolve around their original region of domestication in Western Asia.

Sheep have become an integral part of many linguistic traditions. In the English language, to call someone a sheep or ovine may allude that they are timid and easily led, if not outright stupid. In contradiction to this image, male sheep are often used as symbols of virility and power, such as for the St. Louis Rams and the Dodge Ram. Sheep are key symbols in fables and nursery rhymes like The Wolf in Sheep's Clothing, Little Bo Peep, Baa Baa Black Sheep, and Mary Had a Little Lamb. Novels such as George Orwell's Animal Farm, Philip K. Dick's Do Androids Dream of Electric Sheep? and Thomas Hardy's Far From the Madding Crowd utilize sheep, as either characters or symbols. Poems like William Blake's "The Lamb", and songs such as Pink Floyd's "Sheep" use sheep for metaphorical purposes. In more modern popular culture, Exploding sheep are a video gaming phenomenon. The 2007 film Black Sheep exploits sheep for horror and comedic effect, ironically turning sheep into blood-thirsty killers. The Academy Award-winning film Babe, adapted from Dick King-Smith's The Sheep Pig, revolves around sheep husbandry and utilizes sheep as central characters.

Counting sheep is popularly said to be an aid to sleep, and some ancient systems of counting sheep persist today. Sheep also enter in colloquial sayings and idiom frequently with such phrases as "black sheep". Stereotypically, sheep are proverbial for their willingness to follow others of their kind. Citizens who accept overbearing governments have been referred to by the portmanteau neologism of sheeple. Somewhat differently, the adjective "sheepish" is also used to describe embarrassment.

In religion and folklore

A ram's horn shofar (photo by: Olve Utne)

Religious symbolism and ritual involving sheep began with some of the first recorded faiths. In Ancient Egyptian religion, the ram was the symbol of several gods: Khnum the potter god who was the source of the Nile, Heryshaf and Amun in his incarnation as a god of fertility. Other deities shown with ram features include: the goddess Ishtar, the Phoenecian god Baal-Hamon, and the Babylonian god Ea-Oannes. There are also many ancient Greek references to sheep. The god Pan was strongly associated with flocks and herds, and the legend of Chrysomallos the golden-fleeced ram continues to be told through the modern era, and is the central image of the chivalric Order of the Golden Fleece.

Sheep play a major symbolic and historical part in all the Abrahamic faiths, since Abraham, Isaac, Jacob, Moses, and King David all worked as shepherds. According to the Biblical story of the Binding of Isaac, a ram is sacrificed as a substitute for Issac after an angel stays Abraham's hand. Eid ul-Adha is a major annual festival in Islam in which a sheep is sacrificed in remembrance of this act. Greeks and Romans also sacrificed sheep regularly in religious practice, and Judaism also once sacrificed sheep as part of Korban. Many ovine symbols—such as the Passover lamb and the ceremonial blowing of a shofar—still find a presence in modern Jewish traditions. In Christianity, a congregation is often referred to as a flock, and the Adoration of the shepherds is an important element in the Christian iconography of the Nativity of Jesus in art. Christ is also portrayed as the Sacrificial lamb of God (Agnus Dei) and Easter celebrations in Greece and Romania traditionally feature a meal of Paschal lamb.

The ram is the first sign of the Western astrological zodiac, in which it is known as Aries. The sheep also forms one of the animals associated with the 12-year cycle of in the Chinese zodiac, related to the Chinese calendar. Chinese tradition associates each animal with certain personality attributes, and people born in the year of the sheep are said to be shy, mild-mannered, and artistic, among other traits.

Economic importance

Global Sheep and Lamb stock
in 2005
Number in millions
1. People's Republic of China	170.9 (15.84%)
2. Australia	102.7 (9.52%)
3. European Union (15 nation)	99.3 (9.2%)
4. Russia (former Soviet Union)	65.3 (6.05%)
5. India	62.5 (5.79%)
6. Iran	54 (5%)
7. Sudan	49 (4.54%)
8. New Zealand	39.9 (3.7%)
9. United Kingdom	35.3 (3.27%)
10. South Africa	25.3 (2.34%)
World total	1079.0
Source: UN Food and Agriculture Organization

Domestic sheep have been important to many economies, given that sheep provide a wide array of raw materials. Wool continues to be a vital textile, although in the late 20th century wool prices began to fall dramatically as the result of the popularity and cheap prices for synthetic fabrics. For many shepherds, the cost of shearing is greater than the possible profit from the fleece, making subsisting on wool production alone practically impossible without farm subsidies. Wool has also been used as material in making alternative products such as building insulation. In the 21st century, the sale of meat is the most profitable enterprise in the sheep industry.

Sheepskin is likewise used for making clothes, footwear, rugs, and other products. Byproducts from the slaughter of sheep are also of value: sheep tallow was once used in candlemaking, sheep bone and cartilage has been used to furnish carved items such as dice and buttons as well as rendered glue and gelatin. Sheep intestine can be formed into sausage casings, and lamb intestine has especially been formed into surgical sutures, as well as strings for musical instruments and tennis rackets. Sheep droppings have even been sterilized and mixed with other traditional pulp materials to make paper. Of all sheep byproducts, perhaps the most valuable is lanolin: the water-proof, fatty substance found naturally in sheep's wool and used as a base for innumerable cosmetics and other products.

In the modern era, sheep retain considerable importance in the economies of several countries. After China, the largest producers of sheep products are in the southern hemisphere: Australia, New Zealand and the Patagonian regions of Argentina, Uruguay, and Chile. Sheep play a major role in the economies of several smaller countries where the number of sheep may not be great and impact on the global economy is negligible, but is still important locally. For example, sheep production in the Faroe Islands is of key importance to the local history and economy, but has no perceptible impact on the global sheep meat or wool trade.

As food

Main article: Lamb (food)

Sheep meat and milk were one of the earliest staple proteins consumed by human civilization after the transition from hunting and gathering to agriculture. Sheep meat prepared for food is known as either mutton or lamb. "Mutton" is derived from the Old French "moton", which was the word for sheep used by the Anglo-Norman rulers of 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 (eventually forming the word English speakers use today). More recently, "mutton" has been limited to the meat of older sheep; "lamb" is used for that of younger ones, usually those under a year old.

Lamb shanks

In the 21st century, the nations with the highest consumption of sheep meat are the Persian Gulf states, New Zealand, Australia, Greece, Uruguay, the United Kingdom and Ireland. These countries eat between 14 and 39 lbs. (approximately 3 to 18 kg) of sheep meat per capita, per annum. By comparison, countries such as the U.S. consume only a pound or less (under 0.5 kg). In addition, such countries rarely eat mutton, and may even restrict their habits to the more expensive cuts of lamb: mostly the chop and the leg. In those that do favor sheep meat, it is often the product of a past history of sheep production, even if they produce little or no sheep today. In such countries in particular, dishes comprising alternative cuts and offal may be popular or traditional. Sheep testicles—called animelles or lamb fries in culinary terminology—are considered a delicacy in many parts of the world. Perhaps the most infamous dish of sheep meat is the Scottish haggis, composed of a sheep's heart, liver and lungs cooked within its stomach.

Though it may have been in antiquity, sheep's milk is no longer drunk directly on any appreciable level. Sheep's milk is, however, valuable in the creation of some popular varieties of cheese and yogurts. Containing 6% fat and double the solids of cow's milk, it can be crafted in to such dairy products with relative ease. Well-known sheep milk cheeses include the Roquefort of France, the Brocciu of Corsica, Manchego from Spain, the Pecorino Romano of Italy and Feta of Greece. Sheep milk does contain 4.8% lactose, which may affect those who are intolerant.

In science

Though not common model organisms, sheep have had played a small, yet influential role in scientific experimentation. Several of the few contemporary instances of sheep experimentation has caused a significant impact on science and culture at large. In 1996, a Finnish Dorset sheep named Dolly was the first mammal ever to be cloned from an adult somatic cell. Beginning in 2006, controversy raged over a scientific study at the Oregon Health and Science University, which investigated the biological mechanisms producing homosexuality in rams. Organizations such as PETA actively campaigned against the study, accusing scientists of trying to cure homosexuality in the sheep.

External links

• A to Z of sheep breeds from the British National Sheep Association
• Sheep at Curlie
• Sheep101.info
• A Glossary of sheep terms from the American Sheep Industry Association
• The Domestic Sheep by Henry Stewart (1898), "Natural History" and "Anatomy."