The nutrition of ruminants grazing native and improved pastures. V. Effects of stocking rate and soil ingestion on the copper and selenium status of grazing sheep

Abstract

In experiment 1, sheep ranging in age from newly born to 112 months had greater hepatic copper concentrations at 10 than at 20 sheep/ha but differences in selenium concentration varied between age groups. In experiment 2, sheep aged 29 months were grazed at 10 and 20 sheep/ha and were subjected to liver biopsy at monthly intervals. Hepatic selenium concentrations averaged 0.38 mg/kg DM at the high and 0.56 mg/kg DM at the low stocking rate. Blood selenium concentration was also greater at the lower stocking rate. In experiment 3, grazing sheep were supplemented with two soils collected from areas which supported sheep with high (HS) and low (LS) blood selenium concentrations. Soil HS slightly increased selenium concentration in blood and soil LS had no effect; hepatic copper levels were not affected by giving either soil.