EFFECT OF DIETARY COPPER, IRON, AND MOLYBDENUM ON GROWTH AND COPPER STATUS OF BEEF-COWS AND CALVES

A study was conducted to determine the effects of copper (Cu) depletion by feeding diets high in either iron (Fe) or molybdenum (Mo) on performance and Cu status of beef cows and calves. Thirty-eight 2-yr-old beef heifers, entering the last one-third of gestation, were randomly assigned by expected calving date to one of four diets: 1) control (CON; corn silage-soybean meal-based diet, 4 mg of Cu/kg), 2) control + 600 mg of Fe (as FeCO3)/kg, 3) control + 5 mg of Mo (as Na2MoO4)/kg, and 4) control + 10 mg of Cu (as CuSO4)/kg. From d 28 until after the end of the calving season (d 125), heifers receiving supplemental Cu had higher (P < .05) plasma Cu levels and ceruloplasmin activities than heifers fed the other diets. By d 224, plasma Cu concentrations of heifers fed the CON and Fe diets had increased to levels similar to those observed in the Cu-supplemented heifers, whereas the Mo heifers exhibited the lowest (P < .05) plasma Cu of the four treatments from d 168 through the remainder of the 280-d trial. Plasma Cu concentrations and ceruloplasmin activities were greater (P < .05) in Cu-supplemented than in non-Cu-supplemented calves (diets 1, 2, and 3) from d 168 onward, and the Fe- and Mo-supplemented calves did not differ in either measurement at any time during the trial. Rate of gain did not differ among calves fed the CON, Fe- or Cu-supplemented diets, whereas the Mo-supplemented calves gained at a much slower (P < .05) rate. These data indicate that the deleterious effects of Mo on calf performance may not be due to decreased Cu status alone.