The dairy cow is a magnificent producer of food. In approximately 10 months, a good cow can produce 496 pounds of protein, 784 pounds of energy in the form of the sugar lactose, 560 pounds of fat, and 112 pounds of minerals all in 16,000 pounds of milk. This is enough protein to supply the needs of a man for nearly 10 years, enough energy for 5 years, and enough calcium for 30 years.

The supply of high quality feedstuffs to the cow's highly complex digestive system helps accomplish this wonderful feat. An understanding of this digestive system is a must for making intelligent feeding decisions.

STARTING THE DIGESTIVE PROCESS

Chewing is the first step in processing the feed. This is no small task as the cow makes 40,000 to 60,000 jaw movements per day as it chews and rechews regurgitated feed. Then it passes down a 2 1/2 to 3 foot tube called the esophagus into a large fermentation vat of 40 to 50 gallon capacity. Here digestion of feed goes on by 500,000 billion bacteria and 50 billion protozoa living and multiplying there. These small organisms have several unique characteristics which allow the cow to thrive in situations which would be impossible for other animals to live. They digest fiber found in hay, silage, and pasture for energy, make protein from nitrogen, and synthesize B vitamins for their host, the cow.

FORESTOMACH (RETICULORMEN)

This fermentation vat is composed of two areas called the reticulum and the rumen. The reticulum has a distinctive "honeycomb" appearance. It aids to help bring boluses of feed back up to the mouth for rechewing. It also serves as a receptacle for heavy foreign objects that she eats. A condition known as "Hardware Disease" may occur if a metal object such as wire or a nail is swallowed and punctures the reticulum wall. This condition may prove lethal for two reasons. First, the bacteria and protozoa can contaminate the body cavity resulting in peritonitis and second, the heart and diaphragm may be punctured by the object causing failure of these tissues.

The rumen is, by far, the largest compartment. Its purpose is to store large quantities of feed, keep the feed mixing by strong contractions, and to provide a suitable environment for the bacteria and protozoa to live. This environment is kept agreeable to the microorganisms by maintaining a relatively constant temperature and pH and by removing many of their waste products. Most of the waste products are volatile fatty acids. These volatile fatty acids are the primary sources of energy for the cow. They are absorbed by thousands of "finger-like" projections lining the bottom and sides of the rumen wall. These can be 1/2 inch long and they increase the surface area of the rumen so as to increase her ability to absorb volatile fatty acids.

OMASUM

Once the feed has been reduced in size by chewing and digestion by the bacteria and protozoa, it can pass into a third compartment called the omasum. This area has been nicknamed the "many-plies" due to its unique structure. It has the appearance of an open book with three sides bound. The tissues within are likened to the pages of a book and are called leaves. Up to 100 leaves can be found in the omasum. These leaves have small papillae on them which absorb a large portion of the volatile fatty acids that were not absorbed through the rumen wall. Water and electrolytes such as potassium and sodium are likely absorbed here as well thus drying out the feedstuffs before they enter the next compartment.