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By: Annie Shaw
Published: 2002-07-20

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Digestion occurs when complex materials found in feed are broken down into small fragments that can be absorbed into an animal’s system and then used for growth, maintenance, reproduction and other functions. In ruminants (cows, sheep, goats, deer, etc.) digestion begins when food passes through the mouth, where it is chewed to break up the fibers. The food passes on to the rumen and reticulum – often considered one large organ called the reticulo-rumen – where microbial digestion (or fermentation) takes place. Micro-organisms (MOs) in the rumen and reticulum, such as bacteria and fungi, work to further break down the food. Specifically, they break down the carbohydrates in the diet and manufacture protein to meet the energy and nitrogen needs of the animal. The animal can regurgitate very fibrous material (the ‘cud’) from the rumen for more chewing. After leaving the reticulo-rumen, the partially digested food (digesta) enters the omasum, where water is absorbed. The rumen, reticulum and omasum constitute the foregut, which is the distinguishing feature of ruminants. The digesta then passes on to the hindgut, which includes the abomasum, or ‘true’ stomach, and the intestines. Here the digestive processes are the same as those that occur in other mammals – essentially the enzymatic (rather than microbial) breakdown of the digesta and absorption by the animal of the nutrients.