Why do cows have four stomach compartments?

Answer 1

The four compartments of the cattle stomach are the rumen, reticulum, omasum, and abomasum (Figure 2). The rumen is the largest compartment, and it contains billions of bacteria, protozoa, molds, and yeasts. These microorganisms live in a symbiotic manner with the cow, and they are the reason cattle can eat and digest large amounts of roughage. The rumen microorganisms are adaptable enough that cattle can digest a large variety of feeds from grass, hay, and corn to brewer's grains, corn stalks, silage, and even urea.



The bacteria and protozoa do most of the digestion of feeds for the cow. This is a tremendous factory. There are 25 to 50 billion bacteria and 200 to 500 thousand protozoa in every milliliter of rumen fluid (about 0.06 ounces). The microorganisms digest the plant fiber and produce volatile fatty acids. These fatty acids are absorbed directly through the rumen wall and supply 60 to 80 % of the energy needed by the cow. In addition to energy, the microorganisms produce protein including essential amino acids from the protein and nitrogen the cow ingests. Because the microbes can use nitrogen to make protein, cows can eat urea and other sources of non-protein nitrogen that would kill non-ruminants. The microbes also make vitamins B and C.

The reticulum, with its honeycomb like lining, is a compartment of the stomach that is involved with rumination. It also acts as a trap for foreign objects ingested by the cow. It is not unusual to find rocks, nails, and pieces of wire and metal in the reticulum of cattle. If wire or metal punctures the side of the reticulum, it can cause "hardware disease." Hardware disease is actually an irritation or infection of the diaphragm, heart or lungs. It is hard to treat, but can be prevented by keeping metal trash out of pastures. Specially shaped magnets can be administered to cows to decrease the possibility that ingested metal will pierce the digestive tract. These magnets stay in the reticulum for the life of the animal.

When cattle ruminate, or chew their cud, they are regurgitating a bolus of incompletely chewed feed. In order for the microbes to digest fiber rapidly and efficiently it must be in small pieces, so cattle re-chew their food several times. Cows also eructate or belch giving off carbon dioxide and methane. When cows "lose their cud" or stop ruminating, it is an indication that they have a digestive upset, and their rumen is not functioning properly.

Bloat is another condition that occurs when cows can't eructate. It is caused by a rapid change in feed or overeating grain (gaseous bloat) or grazing pure stands of clover or alfalfa (frothy bloat). Gaseous bloat is a result of improper digestion or fermentation of grain. It is treated by passing a tube into the rumen or using a trocar and cannula to make an external opening in the rumen to release the gas pressure. The procedure may have to be repeated. Frothy bloat is a result of surfactants in legumes causing gas to be trapped in a bubbly foam. Large amounts of mineral oil must be forced into the rumen via a tube to break up the bubbles as a treatment for frothy bloat. Bloat must be treated quickly as the increased rumen size and pressure interferes with normal breathing.

The incidence of bloat in cattle grazing legumes can be reduced by maintaining at least 50% of the stand as grass. Also, cattle should not be turned out onto a pasture with a high percentage of legumes when cattle are hungry or the pasture is wet. Once cattle are adapted to legume/grass pastures, they can graze it even when wet. A final option is to use "bloat guard" blocks which contain poloxolene.

Although rumen microbes can digest a great variety of different feeds, they are very sensitive to drastic changes in feeds. Some groups of microbes are better at digesting fiber (forages), whereas others are better at digesting starch (grains). Changing rapidly from a forage-based diet to a grain-based diet causes millions of fiber-digesting microbes to die-off as they cannot digest the starch, and there are too few starch-digesting microbes to use the grain so the grain sours in the rumen. As a result, rumen pH decreases, the rumen stops working, and the animal becomes ill. In severe cases, cattle can develop acidosis and founder or die.

The omasum is also known as "the book" or many piles because of its many leaf-like folds. It functions as the gateway to the abomasum, filtering large particles back to the reticulorumen and allowing fine particles and fluid to be passed to the abomasum. Though the complete function of this compartment is unknown, it does aid in water resorption and recycling of buffers for the saliva. The omasum may also absorb some volatile fatty acids.

The abomasum is also known as the "true stomach." It functions much like the human stomach producing acid and some enzymes to start protein digestion. Animals that go off feed or have acidosis can develop a displaced abomasum or "twisted stomach." The abomasum will actually float out of place and become torsioned stopping the flow of digesta. Surgery is the only cure for a displaced abomasum. Although displaced abomasum is more common in dairy cattle than beef cattle, producers should be aware of the possibility of this problem in cattle that have had severe digestive upsets.
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Answer 2

Cow's being grazers, take a long time to get all of the nutrients out of grass. It takes a long time to break down cellulose(plant walls, we call it fiber), so they have 4 chambers, only the first chamber regurgitates as cud, it is ground up more so it can go to the next chamber. Horses are different. Did you ever notice that a cow's defecant is just a big pile of goo, and a horses looks like a big human's? It's because the cow's digestion with the "4 stomachs" can break down cellulose, the horse, where speed is important, doesn't have that so it has more cellulose in it's feces. Eat your fiber, make horse turds, not cow patties!

Answer 3

Nurmord is right, except for the anatomy. The first three chambers (rumen, reticulum, and omasum) are not stomachs. They are expanded portions of the esophagus. Only the 4th section, the abomasum is a true stomach. It's a nice adaptation for a prey animal. It can spend 8 hours a day eating, exposed to predators, then spend another 8 hours in a more protected area, ruminating.

Answer 4

Because of the nature of the food they eat. It's tough, it's fibrous, it's not that easy to digest. You try to eat grass and see how much your gut hurts! They do regurgitate their food and chew it again, to break it down as much as possible, and they need the four compartments to break it down enough to get nutrition out of it. When they're babies, one section is much bigger than the others and it's specially made to digest milk, but as they grow and start to eat different things, that section shrinks and the sections to digest grass expand.

Answer 5

I believe it has to do with the way they eat - they pull grass from the fields and do not chew it. Rather it goes into 3 of the compartments and remains there. Then later on, the cow will lay down and 'regurgitate' the stored grass and chew on it properly. "Chewing her cud" is what it's called.