Responses of lactating dairy cows to copper source, supplementation rate, and dietary antagonist (Iron)

Forty-eight lactating Holstein cows were fed low-Cu diets with 500 mg of su pplemental Felkg of dry matter (DM), a Cu antagonist, for a 30-d Cu-depleti on period. After depletion, two Fe treatments (0 and 500 mg of Fe/kg of die tary DM) and five Cu treatments (2 x 5 factorial arrangement) were compared over 83 d. The Cu treatments were control (basal diet containing 8 mg of C u/kg of DM) and either 15 or 30 mg of supplemental Cu/kg of dietary DM from either CuSO4 or Cu-lysine. Feeding 500 mg of supplemental Fe/kg of DM (in addition to basal dietary concentration of 140 mg Fe/kg) depressed liver Cu in the absence of Cu supplementation. Apparent Cu retention, estimated fro m Cu intake minus fecal Cu, was increased greatly by Cu supplementation imm ediately after the depletion period but declined to very low net retention by d 45 of the 83-d experiment. There were no differences detected between CuSO4 and Cu-lysine except a tendency over time for Cu-lysine to maintain h igher plasma Cu, especially in the absence of the Fe antagonist.