Copper status of sheep grazing pastures fertilized with sulfur and molybdenum

Abstract

Varying quantities of sodium molybdate, superphosphate and copper sulfate were applied to 30 plots, and changes in hepatic copper concentration in sheep grazing these plots were measured by using a biopsy technique. A relationship between changes in hepatic copper storage and the copper and sulfur x molybdenum concentrations in the green forage on offer was calculated. This relationship was used to calculate the quantity of copper in green forage on offer necessary to maintain hepatic copper concentration constant when the forage varied in sulfur and molybdenum concentration. In a second experiment sodium molybdate was applied to pasture grazed by sheep at rates varying from 0 to 2000 g molybdenum per ha. Black sheep grazing pasture dressed with 2000 g molybdenum per ha, grew white wool for four months following molybdenum application; this corresponded to the period when molybdenum concentration in herbage on offer was greatest. There were also changes in blood, wool, kidney and liver composition following molybdenum application but these were small when molybdenum was applied at the usual commercial rate. The results of both experiments suggest that the application of molybdenum to pasture at commercial rates is unlikely to induce copper deficiencies in grazing sheep.