Tolerance of inorganic selenium in wether sheep

Abstract

This experiment evaluated the maximum tolerable level of inorganic Se fed to growing wether lambs for 1 year. 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 22.8 ± 3.3 kg were randomly allotted to one of six treatments. Blood samples were collected and liveweight gain determined at 28-day intervals and tissue samples were collected at experiment termination. Serum, whole blood, wool, hooves, bile and five tissues were analyzed for Se concentrations. Five tissues at experiment termination were microscopically evaluated for tissue breakdown due to Se toxicosis. Also, five enzyme activities and albumin were determined. Lamb BW were not influenced by dietary Se concentrations ( P > 0.15). Both serum and whole blood Se concentrations increased at each collection period as dietary Se level increased ( P < 0.01) and the serum had a dietary Se level × time interaction ( P < 0.01). The whole blood Se concentration was two to three times greater than serum Se concentration. There was a strong positive correlation ( r = 0.92) between serum and whole blood Se concentration. At termination of the study, all tissues and wool, hoof, and bile Se concentrations 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, and enzymes were within their respective normal ranges. These results suggest that ≤10 ppm dietary Se as selenite is not toxic to wether lambs when fed for 1 year. 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.