Effect of increasing elemental sulphur and copper intakes on the copper status of grazing sheep

Under some conditions, the use of high-sulphur fertilisers has been thought to be associated with an increase in the incidence of copper deficiency among ruminants grazing the fertilised pastures or fed treated herbage. In this study 35 Romney lambs grazing ryegrass–white clover pasture of low molybdenum content (<0.5 mg Mo/kg DM) received dietary supplements of elemental S and Cu 3 times weekly for 15 weeks. The supplements increased S intake from 3.9 to 7.9 g/day, and increased Cu intake from 9.3 to 24.3 mg Cu/day. Treatment with S significantly increased the total S concentration in strained rumen fluid (SRF), and treatment with Cu increased the Cu concentrations in all fractions of the digesta. In the presence of 4 g S/day, the effect of supplemental Cu on SRF and duodenum soluble Cu concentrations was reduced by about half. Increasing S intake had no effect on plasma and liver Cu concentrations, while increasing Cu intake markedly raised liver Cu concentration. It was concluded that fertilising pastures with elemental S is unlikely to affect the Cu status of grazing sheep, under conditions where pasture Mo concentration is low (<0.5 mg Mo/kg DM).