SELENIUM METABOLISM IN RUMINANTS

The review deals with the most important aspects of selenium in rumina nts. The absorption, distribution, metabolic transformation, secretion in milk and placental transmission of selenium are described. Seleniu m is absorbed in the lower parts of the small intestine, then it is tr ansported to the liver bound to proteins and in a free form. From the liver, selenium is reverted to the blood stream bound to alpha and gam ma globulines, where it is incorporated to selenoproteins, chiefly sel enocistein into gluthatione peroxidase (GSH-Px). The incorporation int o proteins is mediated by gene products called SelA, SelB, SelC and Se lD. After absorption, selenium metabolism in ruminant is similar to no n-ruminant animals. Factors that interfere with selenium metabolism, l ike chemical forms of selenium, level of selenium in blood and tissue before supplementation, presence of some minerals and aminoacids in th e ration, calcium level in the diet, and concentration of selenium in the ration, are described.