Submitted to: Encyclopedia of Animal Science
Publication Type: Book / Chapter
Publication Acceptance Date: 6/5/2003
Publication Date: 11/1/2004
Citation: Ferrell, C.L. 2005. Nutrient requirements: Ruminants. In: Pond, W.G., Bell, A.W., editors. Encyclopedia of Animal Science. Marcel Dekker,Inc., New York, NY. p. 678-680.
Technical Abstract: Nutrient needs of tissues of ruminants are similar to those of nonruminants. Tissues of ruminants require oxygen, water, energy, amino acids, fatty acids, minerals, and fat- and water-soluble vitamins. Dietary needs of ruminants are simpler and often cheaper than for nonruminants, because of anaerobic microbial metabolism in the rumen. Microbial metabolism of dietary intake also increases the complexity of relating dietary intake to nutrients available to the animal. The symbiotic relationship between the animal and microbes within the digestive tract (especially in the rumen and reticulum) results in several unique features of ruminant dietary requirements. In particular, complex carbohydrates, such as cellulose, can be effectively digested and metabolized by rumen microbes. Volatile fatty acids (VFA), byproducts of microbial fermentation of carbohydrates or protein, provide a major proportion of the energy available to ruminants. Dietary protein, amino acids, or nonprotein nitrogen, such as urea, may be incorporated into microbial protein, which serves as the primary source of amino acids to ruminants. Alternatively, amino acids from the diet may "escape" microbial fermentation in the rumen and become available for intestinal absorption. In addition, urea produced within the animal may be "recycled" to the digestive tract, thus providing a source of N for microbial synthesis of amino acids. Similarly, B vitamins, vitamin K, and essential fatty acids are normally produced in sufficient quantities by microbial fermentation to meet animal requirements; however, microbial synthesis of vitamin B12 requires a dietary source of cobalt.