Selenium in Animal Nutrition: Deficiencies in Soils and Forages, Requirements, Supplementation and Toxicity

Selenium (Se), an essential nutrient for animals and humans, occurs as selenoproteins in enzymes. It is very important in animal nutrition because it functions as an anti-oxidant assisted by vitamin E. Se deficiency is a major problem which can be reduced or prevented by supplementation with inorganic or organic sources of Se. However, excessive supplementation and consumption of Se accumulating plants may lead to Se toxicity and animal poisoning. Minimal lethal dose for animals range between 1.5 to 8 mg kg -1 Se live body weight and maximum tolerable concentration of Se in forages is 5 mg kg -1 . Se deficiency in animals also depends greatly on Se content of forages and soils. Se deficient soils contain less than 0.6 mg kg -1 and can be fertilized to increase Se content of forages or pastures for animals. Forages are classified as adequate, marginally deficient and deficient in Se and contain 0.2, 0.1-0.199 and <0.1 mg kg -1 Se respectively. Silages can also be fortified with selenium to meet the requirements for Se in animals. The requirements of Se for animals need to be met to provide adequate animal and human nutrition.