THE EFFECTIVENESS OF USING SUPPLEMENTARY ZINC AND MOLYBDENUM TO REDUCE THE COPPER CONTENT IN THE LIVER OF HYPERCUPROTIC SHEEP

Two trials were conducted to evaluate the effectiveness of different m ethods of reducing the liver copper (Cu) concentration of sheep whose livers had been loaded with Cu, in order to protect the sheep from Cu toxicity, after dietary Cu had been withdrawn. In the first trial 0, 7 5, 150 and 300 mg zinc (Zn) kg-1 feed were added to a basic diet low i n Cu and fed to hypercuprotic sheep (n = 32) for 88 d. At the end of t he trial, liver Cu concentrations (c 800 mg Cu kg-1 DM) in all 4 treat ments did not differ significantly from the Cu concentrations of the l iver biopsy samples taken at the onset of the trial. From other measur ements taken, none of the sheep appeared to be close to the haemolytic phase of chronic Cu toxicity. In the second trial, lasting 79 d, 40 h ypercuprotic sheep were allocated to 4 treatments, viz. a control, a g roup receiving a parenteral treatment of Zn, amounting to approximatel y 7 mg Zn d-1 and 2 further groups receiving molybdenum (Mo) (15 and 3 0 mg Mo sheep-1 d-1), added to the basic diet high in sulphur (4,06 g kg-1 DM). The parenteral Zn treatment did not change liver Cu concentr ations. The 15 mg and 30 mg Mo treatments reduced the Cu in the livers significantly by 24% and 42% respectively. It is suggested that both oral and parenteral Zn supplementation are ineffective in reducing liv er Cu concentration once dietary Cu has been withdrawn from the diet. The supplementation of Mo caused a gradual decrease in plasma aspartat e transaminase activities compared to that of the Control and Zn treat ments. Molybenum supplementation reduced the available Cu concentratio n in plasma which, in some sheep in the 30 mg Mo treatment, reached a concentration indicating a marginal Cu deficiency. It is concluded tha t dietary Mo is effective in reducing liver Cu concentrations, through at the level of 30 mg sheep-1 d-1, an induced Cu deficiency is possib le.