Effects of dietary copper, molybdenum and sulfur on biliary copper and zinc excretion in Simmental and Angus cattle

Abstract

The effect of increased dietary copper (Cu), molybdenum (Mo) and sulfur (S) on biliary Cu and zinc (Zn) excretion was studied in four Angus and four Simmental heifers surgically prepared for bile collection. Initially, two of each breed were fed a low(L)-Cu and two a high(H)-Cu diet for 2 mo. All animals were then transferred sequentially to diets containing LCu–HS for 1.5 mo, HCu–HS for 2 mo, HCu–HMo for 2 mo and HCu–HMo–HS for 2 mo. Bile flow and biliary Cu and Zn concentration were measured on two consecutive days each month. Plasma Cu concentrations were measured once monthly. Biliary Cu concentrations (mg L−1) and bile Cu excretion (mg 6h−1) were greater (P < 0.05) in cattle fed the HCu diet than those fed the LCu diet. The greatest overall excretion of Cu (P < 0.05) occurred during feeding of the HCu–HMo–HS diet. Dietary concentrations of Cu, Mo or S did not affect the biliary Zn concentration except in cattle fed the LCu diet when Zn excretion was low. The present study describes for the first time a breed difference in biliary Cu excretion in cattle. Biliary Cu concentration was higher (P < 0.001) in the Simmental cattle than in the Angus cattle. Biliary Cu excretion during the first day of each 2-d sampling period was significantly higher than during the second day. This was a combined effect of a greater bile flow (P < 0.005) and biliary Cu concentration (P < 0.05). In contrast, both biliary Zn concentration and biliary Zn excretion were higher (P < 0.0001) during the second day of sampling. Diet-related changes in plasma total Cu and the trichloroacetic acid (TCA) - soluble Cu were evident. The highest TCA-soluble Cu concentration was observed during feeding of the HCu diet. A decline in plasma Cu concentration occurred during HS feeding. A TCA-insoluble plasma Cu fraction could be detected only during HCu–HMo–HS feeding. These experiments support the view that at least one of the mechanisms by which excess dietary levels of Mo and S induce hypocuprosis in ruminants is by increasing biliary Cu excretion. Key words: Copper, molybdenum, sulfur, biliary excretion, cattle