Sheep

Basic Information Scientific Classification Sheep Breeds Reproduction Digestive Systems and Digestion of Feeds Dietary Requirements References and Further Reading

Sheep is the common name for a group of grazing mammals that may be either wild or domesticated; the domesticated varieties are amongst the most widely distributed types of domestic animal, found in nearly all countries. Wild sheep species still occur in some parts of the world.

Sheep are thought to have been domesticated about 11,000 years ago in what is now northern Iraq. They descended primarily from the mouflon (Ovis musimon), although recent evidence suggests that the Asian mouflon (Ovis orientalis) also contributed to some of the modern breeds.

Sheep are even-toed, hoofed animals. They are cud-chewing animals with the upper incisor teeth missing and with a four-compartmented stomach. They have paired, hollow, unbranched horns that are not shed. The horns of the adult male, or ram, are massive and spirally curved. The horns of the adult female, or ewe, are short and only slightly curved. Some of the primitive breeds may have more than one pair of horns.

Sheep typically have a long, fairly narrow muzzle and pointed ears. They have a split upper lip and relatively narrow front to the jaw which enables them to be highly selective in terms of their diet. In the wild, the animals are nimble runners and climbers. The female normally bears two young (occasionally three) after a gestation period of about 150 days. Under normal situations with good feeding and animal husbandry, sheep can be expected to produce twins. Under conditions of poorer diet and nutrition only a single lamb will be produced. Sheep may live as long as 20 years.

Sheep belong to the suborder Ruminantia of the order Artiodactyla. They make up the genus Ovis in the family Bovidae.

	Domesticated sheep	Ovis aries	now occur more or less globally
	Bighorn sheep	Ovis canadensis	in western North America
	Dall sheep	Ovis dalli	in northern Canada and Alaska
	Mouflon	Ovis musimon	in Mediterranean countries
	Asian mouflon	Ovis orientalis	in western Asia
	Urial	Ovis vignei	in Afghanistan and Pakistan
	Argali	Ovis ammon	in eastern Asia

Sheep with a family in Peru
Note that the long tails are not docked

Breeds are different types of sheep which man has produced, either directly by selective breeding for particular characteristics (e.g. wool, milk, meat, or general purpose) or indirectly by introducing them to new environments to which they have subsequently adapted. In the latter case it is most likely that there has also been some degree of direct selection, even if only for those individuals that appeared to survive better than others, were easier to handle, or that best fitted the herders' or socio-cultural requirements.

In addition to providing skins and wool for clothing and carpets, meat (lamb or mutton) and milk for drinking and for making cheese, sheep are used to a limited extent as pack animals in mountain areas such as Nepal. Several distinct types of domesticated sheep have been developed and the breeds are adapted to a wide variety of environments. There are over 1,650 known breeds of sheep, some of these now extinct, or endangered (see Table 1 in the discussion on Domestic Animal Diversity). Primitive breeds still resemble their wild ancestors in some respects.

There is normally a significant difference in sheep breeds kept by the smallholder farmer or by larger commercial farmers. The smallholder normally keeps a relatively small flock of pure-breed sheep, whilst under the more exacting requirements of more intensive commercial farming systems cross-breeds are commonly used to produce animals with a particular set of characteristics.

There are several different ways to categorize sheep breeds. Although there may be considerable overlaps between categories, these include:

	Commercial use	There are four categories: meat, wool, dairy and multi-purpose. Most sheep breeds are dual-purpose (e.g. meat and wool). A few are triple-purpose (meat, wool and milk). However, many commercial breeds have been developed with one primary product in mind.
	Production purpose	A useful way to categorize sheep breeds is according to their use in production. For example, "ram" or "ewe" breeds. Ram breeds tend to be those which have greater growth and a heavier carcass, with more meat (high lean to fat ratio, and high meat to bone ratio). Ewe breeds on the other hand are strong in maternal characteristics such as fertility, milking, and ability to care for the new-born lambs. Some breeds are considered dual-purpose because they possess traits which make them equally suitable as either a ram or ewe breed.
	Dairy breeds	All ewes that have lambed should give milk, but some breeds give more than others, and selection processes have resulted in a number of breeds that are kept largely for milk production. Sheep milk has about twice the amount of milk solids as goat milk. As a result, more cheese can be produced per gallon of milk. Dairy sheep, however, produce less milk per animal.

Sheep breeds can also be divided into the following categories based primarily on physical characteristics:

	Short-tailed or Long-tailed breeds	Many primitive breeds of sheep are of the northern short-tailed varieties. One advantage is that the tails do not need to be docked (cut short as a measure primarily designed to prevent fly-strike).
	Fat-tailed breeds	These sheep are so named because they can store large amounts of fat in the tail and the region of the rump. They are common in arid areas and other areas with extremes of climate because of their ability to withstand the extremes of heat, cold and drought. Most of the fat-tailed breeds are also hair breeds (rather than wool).
	Wool or coat type	These include breeds with different amounts and distribution of hair and wool. Within the wool types of sheep, there is considerable difference in the type of fibres that the sheep grow. Hair sheep have little or no wool, do not need shearing, and are suited to tropical climates.
	Fine wooled breeds	Fine wool sheep grow shorter-stapled fleeces in which the wool fibre has a very small diameter.
	Long or Coarse wool breeds	Long or coarse wool sheep grow long-stapled fleeces in which the wool fibre has a very large diameter.
	Medium wool breeds	Medium wool sheep grow wool that is intermediate in fibre diameter and length.
	Crossbred wool	The crossbred wool type sheep produce fibres that are intermediate between fine and medium wool; these breeds are primarily crosses between fine and long wool sheep.

Indigenous sheep breeds in tropical, sub-tropical and other developing countries differ from the northern European breeds. Nearly all the northern European breeds are wooled and many are multipurpose (e.g. meat and wool). Fleeces range from the primitive carpet-wool types (such as the Scottish Blackface) with a coarse, outer coat and a finer inner one, to the high quality garment wool breed, the Merino, with its fleece of fine, relatively uniform fibre diameter. In contrast, indigenous tropical breeds grow either coarse fleeces, or more commonly a coat of short or longer hair with little or no wool. They provide meat, milk and skins (often all three) and occasionally their manure is also utilized for fertilizer or fuel. The coarse-wool or long hairy fleeces are used for carpets, rugs, blankets, and in some regions even tents (for example in Mongolia).

Sheep Breeds used in Kenya

Hair Sheep breeds

Wool and
Dual purpose breeds

Domestic sheep breeding cycles are controlled by a hormone called melatonin, which is produced during the hours of darkness. (In humans melatonin is an important hormone involved in control of sleeping patterns). In mid to northern latitudes breeding in sheep is therefore strongly seasonal, with lambs typically being born in the spring. The annual cycle of the daily photoperiod has been identified as the determining factor, whilst environmental temperature, nutritional status and social interactions may modify it. Essentially, under natural conditions this system of controlling the breeding cycle ensures that the lambs are born at a time of year when there is an increasing availability of food resources. It also means that the ewes should be in good condition for mating as a result of the autumn flush of grass. All ewes loose condition during pregnancy and lactation, so there must be a period between weaning the lamb and the next breeding in order to allow for recovery - in general the longer the better.

Oestrus cycles in sheep range between 14 and 20 days with 17 as the average. Females are in heat on average for 30 hours. Males (rams) are fertile year round and most domestic sheep breeders use 1 ram to 25 to 35 ewes. Gestation averages about 148 days. Both male and female lambs reach sexual maturity within one year.

The selection processes involved in the creation of some modern breeds of sheep has resulted in breeds that are weakly-photoperiod-responsive, or less responsive to the effects of the changes in day-length. This enables, for example, sheep farmers to have a greater control over the timing of breeding and the production of lambs - spreading the season so as to cope with the demands of the market.