Cows are grazers. They live in the midst of the food they eat. The cow lowers its head to the ground and touches the meadow plants (or the hay in its stall) with the front end of its soft, moist snout. The cow does not bite off the plants with its teeth or lips, but reaches out with its rough, muscular tongue, enwraps the plants, and tears them off. It clearly needs to use its tongue in this way - cattle that receive soft feed begin to lick their fellow cows much more than usual. The tongue needs the stimulation of roughage.

After it has torn off a few portions and chewed a bit, the cow swallows a mouthful. This activity continues for a few hours. The food reaches the rumen, the huge first chamber of the four-chambered stomach. Occupying the entire left side of the abdominal cavity, the rumen can hold forty-five gallons.

Digestion in the rumen is facilitated by microorganisms that break down cellulose, the main, hard ­to-digest component of roughage. Bacterial activity, the secretion of digestive juices, and the muscle activity of the rumen are all stimulated by roughage. In fact, the rumen only finishes its development and becomes functional when a calf begins to feed on grass or hay.

When the rumen is about half-full, portions of the partially digested food are regurgitated back into the mouth. Rumination begins. Cows usually lie on the ground while ruminating. They grind their food between their large cheek teeth in rhythmical, circling motions of the lower jaw. You are probably familiar with the picture of calm presented by a herd of cows, lying in a meadow, their activity focused inwardly on grinding and digestion.

Digestion involves an intensive production, circulation, and secretion of body fluids. The process begins in the head. While the cow is ruminating, the saliva glands secrete copious amounts of saliva - up to forty gallons a day. The drier the feed (for example, hay), the more the saliva, and the greater the amount of water a cow drinks. As [E. M.] Kranich points out, functionally one can consider the mouth to be a fifth chamber of the stomach.

After rumination, the food is swallowed, entering first the other three chambers of the stomach and then the small intestine. In these organs, fluids are removed from the food and new digestive juices are secreted until finally the cow has broken down its food to a point where it can be taken up by the blood.

Characteristic for cows is their fluid dung, in contrast to the solid dung of other ruminants like sheep or deer. The cow's large intestine does not absorb as much fluid out of this final section of the digestive tract. In fact, from its moist snout, through the whole digestive tract, and finally in its dung, the cow shows more fluidity than other ruminants.

The digestive process is related to the blood - a fluid organ that connects all organs of the body. For every quart of saliva, three hundred quarts of blood pass through the salivary glands. The other digestive organs are sustained by a similarly strong circulation.

The intensive transformation of substances and secretion of fluids characterizing the digestive process are heightened in the formation and secretion of milk. Substances produced by digestion are withdrawn from the blood in the udder. For every quart of milk, three to five hundred quarts of blood pass through the udder. Glands in the udder then create a wholly new substance - milk. This is not a substance that is used by the cow or excreted; rather, it serves another growing organism -the calf. The cow only begins to produce milk after she has given birth to a calf, and the calf has begun to suck on the teats.

When we build up a picture of the cow in this way, we begin to see the cow as a total organism.

CRAIG HOLDREGE is the director of The Nature Institute. Excerpted from the article "The Cow: Organism or Bioreactor" (Orion, Winter 1997) also available online as "Pharming the Cow" (NetFuture #43; www.netfuture.org/1997/ Mar2097_43htm). Used with the kind permission of the author.