Bioavailability of copper proteinate and copper carbonate relative to copper sulfate in cattle.

Two experiments were conducted to determine the relative bioavailabilities of Cu proteinate, CuCO3, and CuSO4. In Experiment 1, 30 heifers that had been depleted of Cu were us 1. Treatments were control, Cu proteinate A, Cu proteinate B, CuCO3, and CuSO4. Sources provided 50 mg of Cu/d. Supplementation increased plasma Cu by d 21, but there were no differences among the sources. Heifers supplemented with Cu had greater liver Cu concentrations on d 21 than did controls. Heifers receiving CuCO3 had lower liver Cu concentrations than the other heifers. In Experiment 2, 40 heifers were fed diets containing 0.15% of added S and 5 mg of added Mo/kg of DM. Treatments were control, CuSO4, CuCO3, and Cu proteinate A. All sources provided 5 mg of added Cu/kg of DM. Controls and heifers supplemented with CuSO4 had declining plasma Cu concentrations. Supplementation with CuCO3 or Cu proteinate A maintained plasma Cu concentrations. Heifers supplemented with Cu proteinate A had smaller decreases in liver Cu concentrations than did heifers supplemented with other Cu sources. In the absence of high Mo, Cu proteinates were similar in bioavailability to CuSO4. In the presence of high Mo, Cu proteinate A appeared to have a greater bioavailability than CuSO4. Copper carbonate increased or maintained plasma Cu concentrations but was not stored in the liver efficiently.