Comparing Tolerance of Selenium (Se) as Sodium Selenite or Se Yeast on Blood and Tissue Se Concentrations of Ruminants (original) (raw)

The objective of this 60 wk study was to determine the maximum tolerable level of selenium (Se) by feeding Se as sodium selenite or Se yeast at high dietary concentrations to wether sheep. Twenty-eight, two-year-old, Rambouillet-crossbred wethers (137.1 ± 18.7 lb initial body weight) were utilized in a 2 × 4 factorial arrangement with 0.2, 20, 30 and 40 mg/kg dietary Se (as-fed) as either selenite or yeast Se added to a corn-soybean meal basal diet. Average body weight decreased linearly (P < 0.10) as dietary Se level increased, though most wethers gained body weight. Serum Se, whole blood Se, and wool Se concentrations from wethers receiving organic Se were greater (P < 0.01) than those from wethers receiving inorganic Se. Selenium concentrations in brain, diaphragm, heart, hoof, kidney, liver and loin muscle were affected (P < 0.05) by dietary Se concentration, with higher Se concentrations generally observed in tissues from wethers receiving organic Se. Though Se concentrations in serum, blood, wool, and major organs at most times exceeded concentrations previously reported in livestock suffering from Se toxicosis, a pattern of clinical signs of Se toxicosis was not observed in this experiment. Histopathological, microscopic evaluation of liver, kidney, diaphragm, heart, and psoas major muscle did not reveal definitive evidence of Se toxicosis in wethers on any dietary Se treatment. Wethers under our experimental conditions tolerated up to 40 mg/kg dietary Se for 60 wk, though differences in Se source were observed. Contrary to previous thought, the range between optimal and toxic dietary levels is not narrow.