Tolerance of Inorganic Selenium in Ruminants

This experiment evaluated the maximum tolerable level of inorganic Se fed to growing wether lambs for 1 yr. Sodium selenite was added to provide 0.2, 2, 4, 6, 8, and 10 ppm Se to a basal diet. Thirty-nine crossbred wether lambs initially weighing 50.2 ± 7.2 lb were randomly allotted to one of six treatments. Both serum and whole blood Se concentrations increased at each collection period as dietary Se level increased (P<0.01). At termination of the study, all tissues and wool, hoof, and bile Se concentrations had increased as dietary Se level increased (P<0.01). Liver had the highest Se concentration followed by the kidney in all but the lowest treatment of 0.2 ppm. Both gross and microscopic evaluation of tissues revealed no significant lesions for any treatment groups. There was no apparent pathological suggestion of selenosis based on tissue evaluation. Albumin and serum enzyme levels suggestive of tissue breakdown as a result of selenosis did not vary (P>0.15) among treatments. These results suggest that 10 ppm dietary Se as selenite is not toxic to wether lambs when fed for 1 yr. It seems plausible, therefore, to consider the maximum tolerable level of Se as selenite for sheep to be considerably higher than 2 ppm as previously suggested.