SUPPLEMENTARY COPPER FOR GRAZING BEEF CATTLE — INJECTABLE COPPER GLYCINATE, AND COPPER SULFATE IN FREE-CHOICE MINERAL SUPPLEMENTS

Eight herds of beef cattle from Northwestern Manitoba were selected for Cu supplementation trials during the 1974 and 1976 grazing season (four herds in each season). Supplementary Cu was provided as injectable Cu glycinate or as CuSO4 in a free-choice mineral supplement. The treatments were a combination of: (1) one dose of injectable Cu at the start of the pasture season; (2) two doses of injectable Cu, at an interval of approximately 90 days, with the first dose as in (1); (3) CuSO4 added to mineral supplements to provide 0.25 or 0.50% Cu; and (4) injectable Cu, one or two doses during the pasture season, plus 0.25% Cu as CuSO4 in the mineral supplement. Within each herd a cow and her calf were treated as a cow-calf unit. The concentration of Cu in blood serum was used as an indicator of the Cu status of cattle. Forage samples were analyzed for Cu, Mo and total sulfur, and absorption coefficients for Cu and available Cu were calculated. One dose of injectable Cu at the start of the pasture season, or the inclusion of 0.25% Cu as CuSO4 in the mineral supplement, was effective as a Cu supplement where dietary Mo and total S were less than 3 mg/kg and 3 g/kg dry matter, respectively. When Mo and total S concentrations were higher than 3 mg/kg and 3 g/kg dry matter, respectively, doses of injectable Cu provided at a 90-day interval or a Cu concentration greater than 0.25% in the mineral supplement were effective. More than 0.50% Cu, as CuSO4, was required where Mo and total S in forages were in excess of 10 mg/kg and 3 g/kg dry matter, respectively. Inclusion of CuSO4 in the mineral supplement was adequate as a supplement for cows, but the calves did not appear to consume adequate mineral. Injectable Cu was equally effective for cows and calves. An inadequate transfer of Cu via milk was indicated when a cow, but not its calf was provided with injectable Cu. The beneficial influence upon serum Cu of injectable Cu as opposed to Cu in the mineral supplement, depended upon whether the Cu requirement of the cow or its calf was to be met. The level of supplementation to prevent a drop in serum Cu over the pasture season depended upon the concentrations of dietary Mo and S, and their effect upon the coefficient of absorption for Cu. Key words: Supplementary Cu, grazing cattle, injectable Cu glycinate, dietary CuSO4, free-choice mineral supplements