Effects of dietary copper concentration and source on performance and copper status of growing and finishing steers.

Performance and Cu status were measured in growing and finishing steers supplemented with different copper (Cu) concentrations and sources. Sixty Angus (n = 36) and Angus x Hereford (n = 24) steers were stratified by weight and initial liver Cu concentration within a breed and randomly assigned to treatments. Treatments consisted of 1) control (no supplemental Cu); 2) 20 mg Cu/kg DM from Cu sulfate (CuSO4); 3) 40 mg Cu/kg DM from CuSO4; 4) 20 mg Cu/ kg DM from Cu citrate (C6H4Cu2O7); 5) 20 mg Cu/kg DM from Cu proteinate; and 6) 20 mg Cu/kg DM from tribasic Cu chloride (Cu2(OH)3Cl). A corn silage-soybean meal-based diet that was analyzed to contain 10.2 mg of Cu/kg DM was fed for 56 d. Steers were then switched to a high-concentrate diet that was analyzed to contain 4.9 mg of Cu/kg DM. Equal numbers of steers per treatment were slaughtered after receiving the finishing diets for either 101 or 121 d. Performance was not affected by Cu level or source during the growing phase. Gain, feed intake, and feed efficiency were reduced (P < .05) by Cu supplementation during the finishing phase. Plasma and liver Cu concentrations were higher in steers receiving supplemental Cu at the end of both the growing and finishing phases. Steers supplemented with 40 mg Cu/kg DM from CuSO4 had higher (P < .05) liver Cu concentrations than those supplemented with 20 mg Cu/kg DM from CuSO4. Liver Cu concentrations did not increase over the finishing phase relative to liver Cu concentrations at the end of the growing phase. These results indicate that as little as 20 mg/kg of supplemental Cu can reduce performance in finishing steers.