Let's ruminate on it

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 reswallowed.


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's said that ruminants have four stomachs. In reality, their "stomach" has four parts.


Pseudo-ruminants
Camelids (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." Rats and rabbits have similar digestive systems.


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.

The reticulum is closely associated with the rumen. Contents mix continually between both sections. The reticulum looks like a "honey comb" in appearance. Relatively litte 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 sheep
Compartment	Capacity
Reticulum  Rumen  Omasum  Abomasum	1.2 to 2.0 quarts 5.0 to 10.0 gallons 0.5 to 1.0 quarts 2.0 to 3.0 gallons
Small intestines	2.0 to 2.5 gallons (80 ft)
Large intestines	1.5 to 2.0 quarts

Source: Sheep Production Handbook, 2002.


Young 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 innoculated 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.

Because lambs are not born with a functioning rumen, supplemental feeds, such as creep feed, need to be highly digestible. Creep rations typicaly 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.

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 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, which it can easily do.


Not too much grain
Sheep "love" the taste of grain. It's like "candy" to them. They will 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 doesn't get enough forage in its diet, it will pick at another's wool.

Read article The truth about feeding grain to sheep and goats=>


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. It is estimated that cattle and other ruminant livestock contribute 37 percent of the methane that is attributed to human activity, with cows contributing most of that.

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.



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Last updated 19-Apr-2021
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