Trace element and vitamin B12 status of sheep given an oral dose of one, two or four soluble glass pellets containing copper, selenium and cobalt

We investigated the effect of an oral dose of 1, 2 or 4 soluble glass pellets containing cobalt, selenium and copper on the trace element and vitamin B12 status of sheep at pasture. Although the effective life of the pellet was intended to be 1 year, the retention of the pellet in the rumen was sometimes less than 6 months. Despite the apparently short retention period, an oral dose of 1 pellet was sufficient to provide physiologically significant quantities of copper, selenium and vitamin B12 to the animal for at least 45, 32 and 16 weeks respectively. The mean values for untreated sheep and sheep given 1 pellet were respectively 0.49 and 3.11 mmol copper/kg liver (dry matter) at week 45, 1.03 and 1.51 ¦mol selenium/L blood at week 32, and 1.15 and 1.82 nmol vitamin B12/L plasma at week 16. Sheep of normal copper and selenium status may be at risk of copper toxicity if given an oral dose of 2 or more pellets and of selenium toxicity if given 4 or more pellets at the same time. In sheep dosed with 4 pellets, mean liver copper and selenium concentrations exceeded, for 16 and 8 weeks respectively, the concentrations acceptable for human consumption.