These inhabitants and their capabilities turn a cow into a mobile fermentation plant for cellulose. The symbiotic microorganisms produce cellulase enzymes, something no mammal can do on its own. The cellulase breaks down the cell walls of plant materials to release fatty acids into the gut. These fatty acids are absorbed by the cow, and constitute a significant portion of her overall energy budget input. Later, when the food passes into the intestine, absorption of amino acids, lipids, carbohydrates, etc., takes place as in other animals.
Ruminants can usually survive on relatively poor ground unsuitable for other species.
The four divisions of the ruminant stomach are the rumen , the reticulum , the omasum , and the abomasum . A combination of mechanical mastication and cellulase enzymatic action on the hard cellulosic material of the bovine diet permits the breakdown of these otherwise-indigestible materials. Slide 136 shows a section of a rumen . If you examine it first by holding it up to the light you'll see that projecting from the wall are numerous finger-like projections. These are the ruminal papillae , which are somewhat conical in three dimensional view.