Selenium content and glutathione peroxidase activity in tissues of young cattle fed supplemented whole milk diets

Three groups of 5 calves each were fed (from birth to 12 weeks of age) 3 vitamin-mineral supplemented whole milk diets differing only in their selenium (Se) content (0.03, 0.23, and 0.53 microgram/g of solids). Glutathione peroxidase (GSH-Px) activities and Se concentrations were determined in blood at weekly intervals and in selected tissues after 12 weeks. There were marked differences among the tissues in GSH-Px activity, most notably in the liver, lungs, and adrenal glands, depending on whether H2O2 or cumene hydroperoxide was used to assay the enzyme. Tissues having the highest GSH-Px activity on a weight basis, when assayed with the H2O2 substrate, were erythrocytes and testes. Enzyme activity in thymus, brain, striated muscle, adipose tissue, and blood plasma was lowest among the tissues analyzed. The Se concentration on a fresh tissue-weight basis was highest in kidney cortex, intermediate in kidney medulla, testes, liver, and spleen, and lowest in striated muscle, adipose tissue, and blood plasma. The Se concentration was increased in liver, kidney cortex, spleen, and heart, with increasing increments of dietary Se, whereas differences were not observed in testes and adipose tissue.