Ruminants omasum

The contents of the rumen pass steadily into the third chamber of the ruminant stomach , the omasum, where the fatty acids, together with water and salts, are absorbed. These fatty acids provide much of the energy for the ruminant but a price is paid virtually all the carbohydrate in the diet is fermented and almost none enters the body. Consequently, glucose must be synthesised to provide lactose in the lactating animals. The lactic and propionic acids are the precursors for the glucose (Chapter 6). It is unclear if some of this glucose is used by the brain of the ruminant. 

Finally, the contents of the omasum, now a thick slurry of microorganisms, pass into the abomasum into which are secreted acid and proteinases to produce an environment corresponding to that of the human stomach. Some of the microflora passing from the rumen to the omasum die and are digested by the acid and the enzymes. This provides the ruminant not only with an additional energy source but with vitamins and essential amino acids that its own tissues caimot synthesise. 

Ruminants include those animals that we normally think of as cud-chewing, or ruminating animals common examples include cattle, sheep, and goats. The most unusual feature of these animals involves their digestive system, and in particular their multi-compartmented stomach. They are commonly referred to as having four stomachs. The true stomach, that part comparable to the stomach of man, is preceded by 3 other compartments. These are, in order, the rumen, reticulum, omasum, and abomasum. 

Although the transformation of C20 5 and C22 6 by ruminal microorganisms to other fatty acids is evident, the nature of the intermediates and endproducts is less clear. When fish oil was fed to dairy cows, no increase in the flow of any cis, trans CLA to the omasum was observed, including the cis-9, trans-W Cl8 2 isomer (23). However, increased omasal flows of trans-9, transA 1 CLA and several nonconjugated dienes were seen. Several studies reported the accumulation of transAl Cl8 1 in ruminal cultures (53) and omasal contents of cows (23), indicating the potential of the fish oil fatty acids to promote cis-9, trans-W production in body tissues and milk from desaturase activity. 

Fig. 8.5 Diagrammatic representation of the rumen, reticulum, omasum and abomasum of the ruminant, indicating the flow of digesta.

Omasum The third compartment of the ruminant stomach consisting of a spherical organ containing various sized leaves that prevent undigested materials from leaving the rumen and entering the abomasum. It absorbs electrolytes from the bolus. 

Ruminant A mammal that possesses four compartments in the stomach (rumen, reticulum, omasum, abomasum) and is capable of digesting fiber-rich foods. The rumen contains a wide range of anaerobic microorganisms capable of converting cellulose and other fibers—except lignin—into volatile fatty acids that are used as a source of energy. 

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