The impact of high zinc intake on the copper status of dairy cows in New Zealand

Abstract AIM: To determine the effect of a high Zn intake on the concentration of Cu in the liver of dairy cows. METHODS: Sixty non-pregnant, non-lactating, mixed-age Friesian dairy cows were randomised into four groups: unsupplemented control; thrice weekly oral treatment with 350 mg Cu (equivalent to 150 mg Cu/day) as CuSO4.5H2O; a ZnO bolus releasing 6.628 g Zn/day given on Days 0 and 28; and oral treatment with Cu and ZnO boluses. The cows were fed baled silage for the duration of the study (56 days). On Days -12, 14, 28, 42 and 56 liver biopsies were collected for determination of concentrations of Cu, and blood samples for measurement of Cu and Zn in serum. RESULTS: Mean concentrations of Cu in the liver of unsupplemented control cows decreased from an initial 717 (SE 108.5) to 396 (SE 88.0) µmol/kg fresh tissue on Day 28, and then increased to 542 (SE 105.3) µmol/kg fresh tissue on Day 42, before decreasing to 434 (SE 81.6) µmol/kg fresh tissue on Day 56. Administration of ZnO resulted in no change...