Antinutritional Factors in Sorghum: Chemistry, Mode of Action and Effects on Livestock and Poultry

Abstract

Sorghum basically contains two major anti-nutritional factors; tannin, a polyphenolic compound located in the grain and, dhurrin a cyanogenic glucoside located mainly in the aerial shoot and sprouted seeds. Tannins are high in sorghum with brown pericarp and no testa and very low in unpigmented grains. The main anti-nutritional effects of tannins are: reduction in voluntary feed intake due to reduced palatability, diminished digestibility and utilisation of nutrients, adverse effects upon metabolism and toxicity. The level of tannins present in sorghum seems to be the predominant factor that influences its nutritional value. Drying, soaking, grinding and pelleting appear to reduce tannin content in feedstuffs while diet supplementation with methyl group donors like choline and methionine reduce the problems associated with tannins in livestock. Dhurrin, on enzyme action readily yields hydrogen cyanide (HCN). The quantity of HCN in sorghum varies with cultivar and the growth condition but diminishes with age. Excess cyanide ion can quickly produce anoxia of the central nervous system through inactivating the cytochrome oxidase system and death can result within a few seconds. Making fodder into hay or silage however, destroys the poison