Tolerance of the calf for excess copper in milk replacer.

Calves were fed milk replacer containing 10, 50, 200, 500, or 1000 ppm Cu, from 3 d to 45 d of age, to estimate the Cu concentration that would adversely affect calf performance. Weight gains and feed efficiency were similar for 10 and 50 ppm Cu but were reduced at 200 and 500 ppm Cu. All calves survived 500 ppm Cu and lower intakes, but only 4 of 7 calves survived the 1000 ppm concentration. Typical clinical symptoms of chronic Cu toxicity and hemolytic crisis were evident for the 1000 ppm calves before death. Additional 1000 ppm Zn prevented deaths for 1000 ppm Cu, but calf performance was poor. Increased Cu intakes elevated plasma ceruloplasmin and glutamic oxalacetic transaminase activity, reduced packed cell volume (hematocrit), markedly increased fecal excretion of Mo and Zn, increased Cu concentration of liver, muscle, heart, blood, and bile, and decreased Mo and Zn in liver. We found 50 ppm Cu a safe intake where milk replacer contained 48 ppm Zn and 1.1 ppm Mo. However, at lower intakes of these elements, and for longer feeding periods than 6 wk, the calf may be much more susceptible to Cu toxicity.