Sheep belong to the ruminant classification of animals. Ruminants are characterized by their four-chambered stomach and "cud-chewing" behavior. Cud is a food bolus that is regurgitated, rechewed, and re-swallowed.Ruminants There are about 150 different domestic and wild ruminant species including cows, goats, deer, buffalo, bison, giraffe, moose and elk. Ruminant animals are further classified by their foraging behavior: grazers, browsers, or intermediate grazers. Grazers, such as cattle, consume mostly lower quality grasses while browsers such as moose and mule deer stay in the woods and eat highly nutritious twigs and shrubs.Intermediats, such as sheep, goats, and white tail deer, have nutritional requirements midway between grazers and browsers. Of this group, sheep are more of a grazer, while goats and deer are more browsers.The primary difference between ruminants and simple-stomach animals (called monogastrics), such as people, dogs, and pigs is the presence of a four-compartment stomach. The four parts are the rumen, reticulum, omasum, and abomasum. Often it is said that ruminants have four stomachs. In actuality, their "stomach" has four parts.Pseudo-ruminantsCamelids (llamas and alpacas) are sometimes called "small ruminants." They are not. In reality, they are "pseudo-ruminants" because they have a three-compartment stomach instead of four, like ruminants. Horses are not ruminants either. They have an enlarged cecum that allows them to digest fibrous materials, similar to a ruminant. Animals of this type are called "hind-gut fermenters." Rabbits are similar. The hippopotamus is another pseudo-ruminant, but it is a foregut fermenter.The rumen digestive system The rumen occupies a large percentage of the abdominal cavity of the ruminant. It is a large storage space for food that is quickly consumed, then later regurgitated, re-chewed, and re-swallowed in a process called cud-chewing. Rumination or cud chewing occurs primarily when the animal is resting and not eating. Healthy mature sheep will chew their cuds for several hours each day.The rumen is a large fermentation vat. It contains billions of microorganisms, including bacteria and protozoa, which allow ruminants to digest fibrous feeds such as grass, hay, and silage that other animals cannot efficiently utilize. Fermentation in the rumen produces enormous quantities of gas that ruminants get rid of by belching (burping). Anything that interferes with belching is life-threatening to the ruminant and may result in a condition called bloat. Mild cases of bloat can usually be successful treated with an antacid or sodium bicarbonate. Severe cases of bloat can result in death.The reticulum is closely associated with the rumen. Contents mix continually between both sections. The reticulum looks like a "honey comb" in appearance. Relatively little digestive activity occurs in the omasum. It is called "many piles" because it contains many layers of tissue. The abomasum is the "true" stomach of the ruminant. It has a similar function as the stomach of a non-ruminant: secretion of enzymes and acids to break down nutrients.Capacities of digestive tract of mature sheepCompartmentCapacityRumen5.0 to 10.0 gallonsReticulum1.2 to 2.0 quartsOmasum0.5 to 1.0 quartsAbomasum2.0 to 3.0 gallonsSmall intestines2.0 to 2.5 gallons (80 feet)Large intestines1.5 to 2.0 quartsSource: Sheep Production Handbook, 2002Young ruminants At birth, the lamb's rumen and reticulum are not yet functional. As lambs begin to nibble on dry feeds, these two compartments become inoculated with microorganisms. As the microbes multiply and begin to digest feed, they stimulate the growth and development of the rumen and reticulum. The lamb's rumen and reticulum are usually functional by the time the lamb is 50 to 60 days old, sometimes earlier, depending upon diet.Because lambs are not born with a functioning rumen, supplemental feeds, such as creep feed, need to be highly digestible. Creep rations typically consist of feedstuffs that have been cracked, rolled, ground, or pelleted. Cracked corn and soybean meal are common ingredients in creep feed. Creep feeding enhances development of the rumen in the young lamb. In fact, the rumen in creep-fed lambs will develop quicker than the rumen in lambs that are fed strictly a forage diet (or milk diet).Grazers by design Though ruminants can digest grain (starch), their more natural diet is forages: grass, weeds, browse, hay, and silage. If too much grain (starch) is consumed at one time or the diet is switched too quickly to grain, a large amount of lactic acid is produced in the rumen and the pH of the rumen drops. This can be a fatal condition to the ruminant animal. Grain must be introduced slowly to the diet of ruminants to give the rumen time to adjust (to starch), which it can easily do.Not too much grain Sheep "love" the taste of grain. It is like "candy" to them. They will often overeat if grain consumption is not regulated. If grain is slowly introduced to the ruminant's diet, grain can be supplemented and in some cases replace some (even most) of the forage in the diet. Whole grain is better for sheep because it requires them to do their own grinding of the grain. Digestive upsets are less common with whole grain as compared to processed grains (ground, rolled, or cracked). Coarse grain are preferred to finely ground grains.Some forage should always be fed to ruminants to keep their rumens functioning properly and to keep them content. Sometimes, if a sheep does not get enough forage in its diet, it will pick at another's wool.Greenhouse gases An environmental impact of ruminant livestock production is that when ruminants belch (burp), they emit methane, a powerful greenhouse gas. A small amount of methane is also produced from their manure. While estimates for domestic ruminants' contribution to methane emissions are typically overblown (and politicized), ruminants are a source of methane. According to the EPA, 10.2 percent of greenhouse gases caused by humans are methane. Methane from cattle accounts for about 3.7 percent of greenhouse gas emissions. Less methane is produced in intensive livestock systems as compared to more extensive, pastoral systems. This is because grain diets result in less methane being emitted. Scientists are studying other ways to reduce methane production from ruminant livestock. For example, livestock fed certain plants produce less methane. Genetics also affects the amount of methane that a sheep emits. Australian researchers have determined the low emitting trait to be about 20 percent heritable, with some added benefits; the sheep are more efficient. Australian scientists are also testing a vaccine to reduce methane emissions.

Grass, clover, and forbs Mostly sheep eat grass, legumes, forbs, and other pasture plants. They especially love forbs. In fact, it is usually their first choice of food in a pasture. A forb is a broad-leaf plant other than grass. It is a flowering plant. Forbs are often very nutritious. Legumes are forbs. As compared to cattle, sheep eat a greater variety of plants and select a more nutritious diet, though less so than goats. Grazing time Sheep will graze for an average of seven hours per day, mostly in the hours around dawn and in the late afternoon, near sunset. When supplements are fed to pastured sheep, it is best to feed them in the middle of the day so that normal grazing patterns are not disrupted. Weather can also affect grazing patterns. Sheep will spend less time grazing when it is hot.Different plants Sheep in different geographic areas eat different plants. Tropical forages are usually not as nutritious as those that grow in temperate climates. Either protein or energy may be the limiting nutrient in a forage diet. All forages are more nutritious if they are eaten in a vegetative state.Pasture (land) requirements The amount of pasture or range land that it takes to feed a sheep depends upon the quality of the land (soil), the amount and distribution of rainfall, the species of forage, and the management of the pasture. It also depends on the nutrient requirements of the sheep. Lactating ewes and growing lambs have the highest nutritional needs.In dry climates, one acre (or hectare) of pasture or rangeland cannot feed as many sheep as an acre of pasture in a moist climate. An acre of pasture in the wet season (spring and fall) can support more sheep than an acre in the dry season (usually summer).Plants do not grow at the same rate all year round. Cool season plants do most of their growing in cool weather (spring, fall), whereas warm season plants produce the most growth during the warmer months. If different forage species are planted, it is possible to provide year-round grazing for sheep, with snow cover being the only limiting factor.Reproductive rates and lamb growth rates are lower in arid climates than high-rainfall areas that grow more plentiful forage. As a result, wool production tends to be of greater importance in arid and semi-arid environments, as it takes less nutrition to grow good quality wool than to produce milk and raise lambs. A farmer may be able to graze ten sheep on one acre of improved pasture in Maryland, whereas one sheep could require ten acres of native range in West Texas.Stored feed When fresh forage is not available or it is inadequate to meet their dietary requirements, sheep are usually fed stored or harvested feeds: hay, silage, balage, green chop, or crop by-products. Hay is grass that has been mowed (cut) and cured (dried) for use as livestock feed.Silage (short for ensilage) or haylage is green forage that has been fermented and stored in a silo or other system that keeps air out. Moldy silage can cause listeriosis or "circling disease" in sheep. The pieces should be chopped smaller for sheep as compared to cattle,Sometimes, pasture plants are cut, chopped, and brought to the sheep. Fresh harvested forage is called green chop. This "cut-and-carry" system of feeding is common in developing countries, where labor is not a limiting factor. Many types of plants can be cut, chopped, if necessary, and fed to sheep.Supplementation Grain is often fed to sheep with higher nutritional needs, such as pregnant ewes during late gestation, ewes nursing two or more lambs, and lambs with the genetic potential for rapid growth. Grain is the seed part of cereal crops such as corn, barley, wheat, and oats. It is not "unnatural" for sheep to eat grain. They have always eaten the seeds of plants. There are microorganisms in the rumen which can digest the starch in grain.A protein source, such as soybean meal or cottonseed meal is usually added to the grain ration, along with vitamins and minerals to make a 100 percent nutritionally-balanced feed ration. Unbalanced grain rations can lead to a variety of health concerns.Sheep love the taste of grain and can experience digestive problems if they eat too much grain too fast. Grain consumption needs to be regulated, introduced slowly, and gradually increased in the diet. At the same time, any dietary change can disrupt healthy digestion.Ruminants, such as sheep, should always have some roughage (fibrous feed) in their diets. At least a pound per day for sheep is usually recommended. Producers in many parts of the world cannot afford to feed (much) grain to their livestock. Whereas in some parts of the US and in some years, grain is a more economical source of nutrients that forage.By-products By-products from crop production and food processing can also be fed to sheep. This is another advantage of ruminant livestock: they can be fed products that would otherwise go to waste and/or require costly disposal. Examples of by-product feeds include soybean hulls, peanut hulls, corn gluten feed, wheat middlings, and whole cottonseed. Sheep can also be fed pumpkins, apples, onion, and other leftover (or cull) foods. With more corn being used in the production of ethanol, distiller's grains are becoming a more popular (and more economical) feedstuff for sheep and other livestock. Distiller's grains are the solids left after ethanol is made. They are also a by-product of the brewing industry. Distiller's grains can be fed wet or dry, but are usually fed dry. Distiller's grains can contain high levels of phosphorus and sulfur, so their inclusion in sheep and lamb diets is usually limited to a certain amount or percentage.

Benefits of grazing Managed or "prescribed" grazing is good for the environment. A grass-covered sod is the best protection against soil erosion and runoff. The vegetation and soils from grazing lands are a large reservoir for organic carbon.Properly managed grazing lands help reduce atmospheric levels of carbon dioxide and may reduce greenhouse gas accumulation. Private grazing lands provide habitat for two-thirds of our wildlife, water for urban and other users, and visually-appealing open space.Having sheep graze under solar panels has been shown to improve soil health. It enables agrovoltaics: co-production of energy and agricultural products.The Public Domain Some people believe that we should not allow sheep or any other livestock to graze our public range and grasslands, due to the damage that was caused by overgrazing in the past. Past overgrazing was caused by lack of management and should not be a reason to ignore the potential benefits of grazing.Nowadays, rangelands can be improved with managed or "prescribed" grazing, whereby you control how many, when, and for how long livestock graze a certain area. Research has shown that light or moderate grazing is usually more beneficial than no grazing.Grazing fees controversy Farmers and ranchers pay a fee to graze their livestock on land that is owned by the federal government. The current fee is $1.69 per animal unit month (AUM). An AUM is the amount of forage it takes to feed a cow and her calf, one horse, five sheep, or 5 to 7 goats for one month.Class of livestockAnimal unit equivalent1000-lb. cow with calf1.0Calf0.60Yearling calf0.80Mature horse1.25Mature sheep0.20Lamb0.15Mature goat0.15Kid goat0.10Source: Determining Carrying Capacity and Stocking rates, North DakotaSome people think that grazing fees are too low, because they are below the cost of leasing private land. But what they fail to realize is that it usually takes more acres of public land to graze livestock.Ranchers also incur much higher costs on public than private land because they are responsible for making improvements to the land, such as building and repairing fences and developing water sources. They also have to share the land with other uses: mining, forestry, wildlife, hunting, and recreation.Overgrazing Sheep can graze very close to the ground and like other livestock will overgraze, if they are allowed to. Overgrazing can lead to loss of vegetation and soil erosion. However, it can be prevented with good grazing practices. Wildlife are also "guilty" of overgrazing.

Sheep and goats have long been used to control unwanted vegetation. Their use has increased in recent years because of the desire for biological control agents in environmentally sensitive areas. Grazing is also a more economical alternative in many situations. Sheep mostly graze forbs (flowering plants) and grass while goats prefer shrubs and other woody plant material.Noxious weedsSheep are currently being used throughout the Great Plains and Intermountain regions to control noxious and invasive weeds. Many of these weeds could not be controlled by means of chemical, mechanical or cultural practices due to the high cost associated with these control methods or their relative ineffectiveness. One such weed is leafy spurge (Euphorbia esula), a Eurasian weed which has consumed millions of acres and is so competitive that it quickly crowds out all other plants to form a monoculture. Another weed, which has impacted many areas throughout the West, is Spotted Knapweed (Centaureamaculosa). This weed invades native ranges and threatens even pristine areas such as our national parks. Sheep readily graze knapweed and are being looked at as another tool to fight this aggressive invader.Sheep will readily consume kudzu (Pueraria montana), a vine that completely replaces all vegetation where it grows in the Southeast. Larkspur (Delphinium sp.) is a weed that is poisonous to cattle. Because sheep can tolerate up to 3 to 4 times more larkspur than cattle, they can be used to help control the weed in cattle pastures.Sheep will voluntarily graze and sustainably control sericea lespedeza (Lespedeza cuneata), a noxious weed in some states. An added benefit is that the condensed tannins found in lespedeza have an inhibitory effect on internal parasites (worms). In fact, in some states, sericea lespedeza is recommended as a safe, nutritious pasture for small ruminants.Preventing wildfires Sheep are being used in many places to reduce the threat of wildfire in areas where wildlands interface with urban communities. This method of reducing wildfire is called creating a “fuel break.” The goal is to reduce the amount of fuel, reduce vegetation height, and create an effective firebreak.Improving plant biodiversity Numerous studies have shown how sheep and goats, used under prescribed conditions, can help increase the plant biodiversity on western ranges. Since sheep prefer to graze and bed on upland areas away from wet lowlands, they are easier to manage in grazing areas where critical riparian and watershed issues are a concern.When sheep are grazed in the same areas for several years, the level of perennial grasses within the plant community tends to increase which has been shown to increase water infiltration and decrease erosion.Improving wildlife habitat Prescribed sheep grazing has been shown to enhance wildlife habitat in a variety of ways. By allowing sheep to graze different areas at specific times of the year, the quality and quantity of certain critical vegetation types can be enhanced.Tree plantations Sheep producers in Canada have been paid to graze newly planted tree plantations with sheep. This method of prescribed grazing increases the viability of the new tree seedlings by reducing the competition of grasses, forbs and weedy species for water, soil nutrients and sunlight. "Trained" sheep have been used to graze in vineyards.Grazing under powerlines Power companies are “hiring” sheep (and goat) herds to keep areas under power lines in forested areas grazed, thus reducing the chance that an errant spark from the lines might start a wildfire and destroy the power line and surrounding forest.Solar grazing Many of the growing number of solar arrays utilize sheep for vegetation control. Combining the two activities provides both an economic and environmental benefit. Most of the vegetation under the solar panels is available for grazing. Without the sheep, the site would need to be mowed frequently and sprayed with herbicides. Hefted sheep The extensive grazing of hefted sheep on the commonland of Britain is a unique phenomenon in Europe, enabling livestock to be kept in unfenced areas without constant shepherding. Each hefted flock has its own territory and is self-confining to that area, a heft. Extended areas are divided into numerous hefts, with each flock knowing its own area and returning to it after lambing, veterinary treatment or other husbandry requirements.Hefted sheep are integral to maintaining the unique and "wild" or semi-natural environment of which they form part. Unfortunately, the numbers of hefted sheep were reduced drastically by the British government during the 2001 foot-and-mouth disease outbreak. Misguided politics continues to challenge this age-old practice.