Contribution of dietary sulphur to the interaction between selenium and copper in sheep

Abstract

The effect of concentration of sulphur (S) in a diet on the interrelationship between copper (Cu) and selenium (Se) metabolism was investigated in sheep. The animals received a sheep finishing diet in individual feeding pens for a period of 74 days. The minerals were included in the diets according to a 3×2×2 factorial experimental design. The final mixtures contained three concentrations of Se; 0·35, 0·88 and 1·34 mg Se (Se added as Na₂SeO₃); two concentrations of Cu; 6·7 and 17·0 mg Cu (Cu added as CuSO₄) and two concentrations of S; 2·15 and 3·97 g S (S added as Na₂SO₄)/kg dry matter (DM). An increase in dietary Cu resulted in a significant (P<0·01) increase in liver Se concentration; 2·30 v. 3·43 mg Se/kg DM for the low v. the high Cu treatments. The addition of S reduced the hepatic Se concentration significantly (P<0·01). This was most pronounced at the high Cu intake, resulting in a significant (P<0·05) three-way interaction between the three minerals, i.e. the hepatic Se concentrations were 2·53, 2·08, 4·07 and 2·79 mg/kg DM for the low Cu–low S, low Cu–high S, high Cu–low S and high Cu–high S treatments, respectively. Dietary S reduced (P<0·01) the concentration of Cu in the liver from 678 mg/kg DM at the low S to 305 mg/kg DM at the high S intakes. Dietary Se did not change the concentration of Cu in the liver significantly. Adding S to the diet caused a reduction (P<0·01) in the Se concentration of rumen bacteria, i.e. from 3·48 mg/kg DM in the low S to 1·96 mg/kg DM in the high S treatments. Selenium concentrations in rumen bacteria and the liver were the most sensitive to changes in Se intake, followed by the heart, muscle, plasma and whole blood. It was concluded that an increase in S intakes would decrease the accumulation of both Cu and Se in the liver of sheep, resulting in a diminishing degree of interaction between Cu and Se.