The effects of supplementary copper and a mineral mix on the development of lupinosis in sheep

Abstract

Lupinosis in grazing sheep is often associated with a potentially deleterious increase in the concentration of copper in the liver. Siromin«, a mineral mix developed by CSIRO for sheep on dry herbage and containing Cu at 116 mg/kg, was tested for its suitability for use with sheep consuming toxic lupin stubble, taking particular regard for dangers of Cu toxicity. There were three dietary treatments applied at two levels (either present or absent) to 40 Merino wethers for 8 weeks. Treatments consisted of adding Cu (10 mg Cu as CuS04/kg), minerals (25 g/kg as Siromin«) and toxic lupin stubble (50 g/kg) to a basal diet consisting of oaten hay and lupin seed and containing 3 mg/kg of Cu. Toxic lupin stubble decreased feed intake and growth, increased plasma activities of liver enzymes and increased plasma concentrations of protein, globulin, bilirubin, Cu and Zn. It also decreased concentrations of Zn and Fe in liver, but had no effect on Cu. The mineral mix had no adverse effects on any signs of lupinosis, and it did not increase liver Cu concentration at either level of dietary Cu. The mineral mix prevented the inappetence caused by lupinosis in sheep fed the low Cu basal diet. Cu treatment resulted in increased concentrations of Cu and Fe in liver, and exacerbated some signs of lupinosis. The results show that the mineral mix is safe to feed to sheep grazing toxic lupin stubble, and it may provide a practical means of supplying additional Zn. The exacerbation of signs of lupinosis by the addition of only 10 mg Cu/kg as CuS04 suggests that under field conditions the supply of Cu in the absence of suitable amounts of molybdenum and sulfur should be kept to a minimum.