How does a ruminant animal digests pasture using rumen reticulum microbes and fermentation?

Answer 1

Actually, the microbes are the key to this question. The rumen and reticulum are just the holding vats of where the fodder from the pasture are digested and provides the mechanical form of digestion, and fermentation is the chemical process that is created by the microbes in the rumen in an anaerobic environment. Put all these together and you have your answer.

Ruminants rely on these microbes to break down the plant matter and release the nutrients from these plants--as well as synthesize their own, like Vitamin B12--in order to get the necessary energy, protein, vitamins and minerals for maintaining body function and meet other physiological requirements like growth, lactation and reproduction. These microbes synthesize an enzyme called cellulase which is designed to break down cellulose, an organic compound found in all plants (and is what gives all plants their structure and support) in order to accomplish this. The anaerobic environment is created when these microbes release carbon dioxide, methane and other organic gaseous or liquid compounds, and these gases need to be released regularly via eructation (or burping). A cow will burp once every minute of every day.

The microbes can't completely break down plant matter, though, so when the cow has eaten her fill, she regurgitates a bolus of partly digested digesta and rechews it, her saliva and chewing actions further breaking it down before swallowing and bringing up another bolus to chew again. This is called "chewing the cud." Her saliva does not have the enzyme to break down starch, but it does act as a buffer to maintain the pH (or acidity) level neutral in the rumen. A cow can easily produce 50 gallons of saliva per day.

The reticulum acts as part of the digestion process, acting as a storage place for foreign objects, and "readying" a part of the digesta from the rumen to be regurgitated and rechewed as cud. However, fermentation also takes place in this stomach chamber, but not nearly as much as in the rumen. (Note: if someone tells you that the rumen is a "storage" area, this isn't entirely true. An organ doesn't act as a storage area if something is constantly being done to the objects inside. The rumen is a home for millions of bacteria, fungi and protozoa, and is very much an ecological environment where these tiny organisms live and die.) The reticulum is known as the "hardware stomach."

Other organs not mentioned are just as important with ruminant digestion. After the plant matter has been digested, fermented, rechewed and fermented again enough, it goes to the third forestomach, called the omasum. Here water is removed from the many folds in this stomach chamber. From there, it moves into the abomasum, or the true stomach of the ruminant animal. The abomasum acts and secretes stomach acid and enzymes very much like our stomachs do. The rest of the digestion process follows like any other mammal.