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 supplemental Fe/kg of dry matter (DM), a Cu antagonist, for a 30-d Cu-depletion period. After depletion, two Fe treatments (0 and 500 mg of Fe/kg of dietary 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 Cu/kg of DM) and either 15 or 30 mg of supplemental Cu/kg of dietary DM from either CuSO4 or Cu-lysine.