Domestic sheep
Domestic sheep (Ovis aries) are quadrupedal, ruminant mammals kept as livestock. Like all ruminants, sheep are even-toed ungulates, also commonly called cloven-hoofed animals. Although the name "sheep" applies to many species, in everyday usage it almost always refers to Ovis aries. Domestic sheep are the most numerous species in their genus, numbering a little over 1 billion, and are most likely descended from the wild mouflon of Europe and Asia.
One of the earliest animals to be domesticated for agricultural purposes, sheep are primarily valued for their 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 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 practised throughout the inhabited world, and has played a pivotal role in many civilizations. In the modern era, Australia, New Zealand, the Patagonian nations, and the United Kingdom are most closely associated with sheep production. Sheep-raising has a large lexicon of unique terms which vary considerably by region and dialect. Use of the word sheep began in Middle English as a derivation of the Old English word sceap; 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 specific 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, sheep have a deeply entrenched place in human culture, and find representation in much modern language and symbology. 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. In contemporary English language usage, people who are timid, easily led, or stupid are often compared to sheep.
Etymology
Etymologically, the word modern English language speakers now use to denote ovines is derived from the Old English term sceap, which is akin to the Old High German scaf and probably ultimately originated from Proto-Germanic or Gothic.
The word "ram" derives from the Old English rom (dated to 725) and subsequently ramm (in use before 1325).[ The word has always been closely associated with implements used in the application of force, such as the battering ram or the weight of a pile driver, but its earliest usage is in reference to male sheep.][ Before 1300, ewe was usually written as ouwe, and it stems from the Old English eowu.][ Lamb is thought to be the oldest ovine term still used in an unchanged form; its first appearance is in 858.][ It sprang from the Old English lomb (dated to 725), and the verb form is first recorded from 1611.]
Description
Domestic sheep are relatively small ruminants, typically with horns forming a lateral spiral and crimped hair called wool. Domestic sheep differ from their wild relatives and ancestors in several respects, having become uniquely neotenic as a result of man's influence.[Budiansky, pp. 97–98.][Budianksy, pp. 100–01.] 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 (polled), or horns in both sexes (as in wild sheep), or in males only. Most horned breeds have a single pair.
Another trait unique to sheep are their wide variation in color. Wild sheep are largely variations of brown hues. Colors of domestic sheep range from pure white to dark chocolate brown and even spotted or piebald.[ 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.]
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 100 and 225 pounds (45–100 kg), with the larger rams between 100 and 350 pounds (45–160 kg).]
The front teeth are gradually lost as sheep age, making it harder for them to feed and hindering the health and productivity of the animal. For this reason, domestic sheep on normal pasture begin to slowly decline from four years on, and the average life expectancy of a sheep is 10 to 12 years, though some sheep may live as long as 20 years.[Ensminger][Smith et al.]
Sheep have good hearing, and are sensitive to noise when being handled.[Smith et al., p. 5.] Sheep have horizontal slit-shaped pupils, possessing excellent peripheral vision; with visual fields of approximately 270° to 320°, sheep can see behind themselves without turning their heads.[Weaver] However, sheep have poor depth perception; shadows and dips in the ground may cause sheep to balk. In general, sheep have a tendency to move out of the dark and into well-lit areas.[ 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 interdigital glands might also be used in reproduction,][ but alternative reasons, such as secretion of a waste product or a scent marker to help lost sheep find their flock, have also been proposed.][Smith et al., p. 4.]
Sheep and goats are closely related (both are in the subfamily Caprinae), and it can be difficult to distinguish them by their appearance. 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, and is not to be confused with the genetic chimera called a geep. Visual differences between sheep and goats include the beard and divided upper lip unique to goats. 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 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, and the more than 200 breeds now in existence were created to serve these diverse purposes.[ Almost all sheep are classified as being best suited to furnishing a certain product: wool, meat, milk, hides, or a combination in a dual-purpose breed. 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 especially stressed in the UK, where breeds are described as either upland (hill or mountain) or lowland breeds.]
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 are hardy, and have good reproductive and mothering capabilities—they are for replacing breeding ewes in standing flocks. Ram breeds are selected for rapid growth and carcass quality, and are mated with ewe breeds to produce meat lambs. Lowland and upland breeds are also crossed in this fashion, with the hardy hill ewes crossed with larger, fast-growing lowland rams to produce ewes called mules, which can then be crossed with meat-type rams to produce prime market lambs.[ Many breeds, especially rare or primitive ones, fall into no clear category.]
Breeds are 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. The record for the most valuable sheep belongs to an Australian Merino ram that was sold for $16,000 AUD.
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.
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 do produce a higher quantity of milk and have slightly longer lactation curves.[Pulina et al p. 2.]
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 wooled and hair breeds. For meat and hide producers, hair sheep are cheaper to keep, as they do not need shearing.[ Hair sheep are also resistant to parasites and hot weather.]
With the modern rise of corporate agribusiness and the decline of localized family farms, many breeds of sheep are in danger of extinction. The Rare Breeds Survival Trust of the UK lists 25 native breeds as having only 3,000 registered animals, and the American Livestock Breeds Conservancy lists 14 as having fewer than 10,000.[ Those that remain are maintained through the efforts of conservation organizations, breed registries, and individual farmers dedicated to their preservation.]
Diet
Sheep are exclusively herbivorous mammals. Like all ruminants, sheep have a complex digestive system composed of four chambers, allowing them to break down cellulose from stems, leaves, and seed hulls into simpler carbohydrates. When sheep graze, vegetation is chewed into a mass called a bolus, which is then passed into the first chamber: the rumen. The rumen is a 5- to 10-gallon (19–38 l) organ which ferments feed via a symbiotic relationship with the bacteria, protozoa, and yeasts of the gut flora.[Simmons & Ekarius, p. 146.] The bolus is periodically regurgitated back to the mouth as cud for additional chewing and salivation.[ Cud chewing is an adaptation allowing ruminants to graze more quickly in the morning, and then fully chew and digest feed later in the day.][Smith et al., p. 56.] This is beneficial as grazing, which requires lowering the head, leaves sheep vulnerable to predators, while cud chewing does not.
During fermentation, the rumen produces gas that must be expelled; disturbances of the organ, such as sudden changes in a sheep's diet, can cause potentially fatal conditions such as bloat. After fermentation in the rumen, feed passes in to the reticulum and the omasum; special feeds such as grains may bypass the rumen altogether. After the first three chambers, food moves in to the abomasum for final digestion before processing by the intestines. The abomasum is the only one of the three chambers analogous to the human stomach (being the only one that absorbs nutrients for use as energy), and is sometimes called the "true stomach".[Simmons & Ekarius, p. 171.]
Sheep follow a diurnal pattern of activity, feeding from dawn to 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.[Simmons & Ekarius, p. 82.] 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) oak and acorns, tomato, yew, rhubarb, potato, and rhododendron.[Simmons & Ekarius, p. 160.]
Sheep are largely grazing herbivores, unlike browsing animals such as goats and deer that prefer taller foliage. With a much narrower face, sheep crop plants very close to the ground and can overgraze a pasture much faster than cattle.[ For this reason, many shepherds use managed grazing, where a flock is rotated through multiple pastures, giving plants time to recover.][ Paradoxically, sheep can both cause and solve the spread of invasive plant species. By disturbing the natural state of pasture, sheep and other livestock can pave the way for invasive plants. However, sheep also prefer to eat invasives such as cheatgrass, leafy spurge, kudzu and spotted knapweed over native species such as sagebrush, making grazing sheep an effective way of restoring native pastures.][Simmons & Ekarius, p. 143.]
Other than forage, the other staple feed for sheep is hay, often during the winter months. The ability to thrive solely on pasture (even without hay) varies with breed, but all sheep can survive on this diet.[ 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.[Wooster, p. 64.] 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 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.[ Although there is a growing movement advocating alternative farming styles, a large percentage of beef cattle, pigs, and poultry are still produced under such conditions.][ In contrast, only a few specific categories of sheep are regularly given high-concentration grain feed, much less kept in confinement. Where there is not enough pasture available or the pasture is not rich enough, sheep producers may fatten market lambs before slaughter (called "finishing"), sometimes in feedlots.][ Many sheep breeders flush ewes and rams with grain during breeding to increase fertility.][Smith et al., p. 101.] Ewes are also flushed during pregnancy to increase birth weights, as 70% of a lamb's growth occurs in the last five to six weeks of gestation.[ Otherwise, only lactating ewes and especially old or infirm sheep are commonly provided with grain.][ Feed provided to sheep must be specially formulated, as most cattle, poultry, pig, and even some goat feeds contain levels of copper that are lethal to sheep.][ The same danger applies to mineral supplements such as salt licks.][Simmons & Ekarius, p. 159.]
Behavior and intelligence
Sheep are prey animals with a strong gregarious instinct, and a majority of sheep behaviors can be understood in these terms. The dominance hierarchy of Ovis aries and its natural inclination to follow a leader to new pastures were the pivotal factors in it being one of the first domesticated livestock species.[Budiansky] All sheep have a tendency to congregate close to other members of a flock, although this behavior varies with breed.[ Farmers exploit this behavior to keep sheep together on unfenced pastures and to move them more easily. Shepherds may also use sheepdogs in this effort, whose highly bred herding ability can assist in moving flocks. Sheep are also extremely food-oriented, and association of humans with regular feeding often results in sheep soliciting people for food.][Budiasnky p. 100 et al.] Those who are moving sheep may exploit this behavior by leading sheep with buckets of feed, rather than forcing their movements with herding.[Budiansky p. 100.][Wooster pp. 73, 75.]
In regions where sheep have no natural predators, none of the native breeds of sheep exhibit a strong flocking behavior.[ Sheep can also become hefted to one particular local pasture (heft) so they do not roam freely in unfenced landscapes. Ewes teach the heft to their lambs, and if whole flocks are culled it must be retaught to the replacement animals.]
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 few other sheep.[ For sheep, the primary defense mechanism is simply to flee from danger when their flight zone is crossed. Secondly, cornered sheep may charge or threaten to do so through hoof stamping and aggressive posture. This is particularly true for ewes with newborn lambs.]
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 s.[Simmons & Ekarius, p. 8.] Primarily among rams, horn size is a factor in the flock hierarchy.[Budiansky p. 78.] Rams with different size horns may be less inclined to fight to establish pecking order, while rams with similarly sized horns are more so.
Sheep become highly stressed when separated from their flock members.[ Sheep can recognize individual human and ovine faces, and remember them for years.][te journal|last=Morell|first=Virginia|date=March|year=2008|title=Animal Minds|periodical=]
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