Effect of copper and iron on neutrophil function and humoral immunity of gestating beef cattle

Eighty gestating beef cattle were used to determine the effect of trace mineral salt mixtures containing copper (Cu) and iron (Fe) on selected immune functions and factors affecting copper bioavailability. Pastured cattle were randomly assigned to receive one of the following combinations of Cu and Fe in the free-choice trace mineral salt: (1) 0 mg of Cu/0 mg of Fe/kg of trace mineral salt, (2) 1,600 mg of Cu (CuSO₄)/3,000 mg of Fe/kg of trace mineral salt, (3) 1,600 mg of Cu (CuSO₄)/0 mg of Fe/kg of trace mineral salt, and (4) 1,600 mg of Cu (CuCO₃)/3,000 mg of Fe/kg of trace mineral salt. Total Cu/Fe consumption (from trace mineral salt) was 2/678, 193/1,050, 162/553, and 202/1,140 mg/head/d, respectively, for the 4 groups. After a 1-month period of acclimation and also on day 28 of the 36-day study, copper concentrations in serum were significantly (P < 0.05) lower in group 1 than in groups 3 and 4. Serum copper concentrations did not increase with time for any group, whereas hepatic copper concentrations increased significantly (P < 0.05) with time for all groups except group 1. Hepatic iron concentrations were similar among groups at the time of the initial and final hepatic biopsies on days 0 and 28, respectively. Hepatic iron concentrations increased significantly (P < 0.05) with time in groups 3 and 4. Humoral response to chicken γ-globulin was high but did not differ among groups on any of the days analyzed. Neutrophil function tests, consisting of hydrogen peroxide production, phagocytosis of latex particles, calcium uptake, and superoxide production, were different only for phagocytosis among groups; the percentage of neutrophils phagocytizing latex beads was significantly (P < 0.05) lower for group 2 than the other groups. A similar reduction in phagocytosis was prevented by the omission of additional Fe from the trace mineral salt (groups 1 and 3) or use of CuCO₃ (group 4).