Posted 5-4-00

Technically, ruminant animals--cows, in this case--do not really have four stomachs. Rather, it's a combination of four stomach chambers called the rumen, reticulum, omasum, and abomasum. They're considered part of a stomach complex. The first three compartments (the rumen, reticulum, and omasum) are highly specialized tissues that allow the animal to digest grasses (see illustration link below!)

The animals themselves do not have the natural ability to make the digestive enzymes required to break down grasses. But their rumen is a very large vat that provides a suitable environment, or "home," for millions of microbes that DO have the capability to digest the grasses. This process is called fermentation.

The relationship between the cow and microbes is called symbiotic because it is beneficial, or helpful, to both of them. After grasses (and other feed components, too) are digested in the rumen, the reticulum and omasum help by sorting out the feed particles that need to go on to the abomasum. This includes particles that need to be further digested in the rumen. The result of digesting feed this way is the production of more microbes, and microbial products from the fermentation process.

Both of these are beneficial to the ruminant animal because the resulting products of fermentation are absorbed into the blood. There, they are used to make other products like milk, muscle (proteins), and fat. And, the microbes themselves spill over into the abomasum, which is very much like a human's stomach. In the abomasum, the microbes are digested in acid. The protein, carbohydrates, and fat, meanwhile, are absorbed in the small intestines the same as in simple stomach animals.

For a cartoon illustration, we suggest checking out this Web address: http://www.mteam.com/cow4.html. Just shade, copy and paste it from here into your computer's address box. Click here to go back up.

-- Sci4Kids, and Randy Baldwin, animal scientist, Energy Metabolism Unit, Nutrient Conservation and Metabolism Laboratory, Beltsville, Maryland.

Back to Archives/ Go home instead