by Debby Richardson

Created on: January 22, 2007   Last Updated: April 30, 2007

Although a cow has no upper front teeth, it grazes up to 8 hours a day, taking in about 45 kg (100 lb) of feed and the equivalent of a bath tub full of water. A healthy cow gives about 200,000 glasses of milk in her lifetime.

You may have heard it said that cows have "four stomachs." In an anatomic sense this is incorrect; there really is only one stomach, but it does have divisions. The first three divisions of the ruminant stomach are sometimes considered to be diverticula of the esophagus; there is considerable debate on this point, however, and some authorities consider them derivatives of the stomach. In any event, they are all derived from the primitive embryonic foregut.

For the most part, the digestive system of ruminants is very similar to that of other mammals, but the stomach is considerably different from the so-called "monogastric" condition. The word "ruminant" comes from the Latin ruminare, to think; and as wildly laughable as the idea of a cow "thinking" may be, nevertheless, the contemplative and placid expression on a cow's face as she "chews her cud" does sort of give the impression that she's dealing with serious world problems.

The four divisions of the ruminant stomach are the rumen, the reticulum, the omasum, and the abomasum. In a functional sense, these operate as parts of a "stomach system" and we can correctly speak of a cow having "forestomachs," if not "four stomachs."

The rumen is an enormous space filled with chewed and half-chewed materials the cow has ingested, swallowed, regurgitated, and swallowed again (often several times).

Reticulum consists of bands of smooth muscle which run through the tops of the ridges of the honeycomb, and which are more or less isolated from the lower levels, nearer the wall.

Omasum has a muscularis mucosae which underlies the epithelium; but in addition to muscularis mucosae, there is an excursion of smooth muscle from the tunica muscularis up between the folds of the muscularis mucosae.

Abomasum is a portion is the true glandular stomach of ruminants. Its histology is very similar to the fundic region of the stomach of monogastric animals, and you will find it instructive to compare it to some of those slides used in the exercise on esophagus and stomach.

Cattle prone to eating an astonishing variety of things that aren't edible. High up on the list of junk that cows will ingest is bits of wire, usually clipped off a hay bale's binding. These indigestible sharp objects can easily cause serious problems, as you might imagine, when they puncture the wall of the forestomach. One way to deal with this is to have the cow swallow a magnet, which attracts and holds the ferrous metals and prevents them from migrating to a place where they can do damage as they slosh around in the vast caverns of the forestomach. There's a brisk trade in recycling these "cow magnets," which are recovered at slaughter and re-used.

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