Effect of differing amounts of zinc oxide supplementation on the antioxidant status and zinc metabolism in newborn dairy calves

This study aimed to evaluate the effects of various amounts of zinc oxide (ZnO) supplementation on growth performance, incidence of diarrhea, micronutrient contents in feces and serum, antioxidant indicators and the concentrations of key enzymes and proteins involved in zinc metabolism in dairy calves. Forty newborn Holstein dairy calves were assigned to one of five groups according to a randomized complete block design: a control group (without zinc supplementation), or groups that received ZnO supplementation at 25.79, 51.58, 103.16, and 154.74 mg/d, yielding an amount of zinc consumption of 20 (Zn-20), 40 (Zn-40), 80 (Zn-80), and 120 (Zn-120) mg/d, respectively, during the experimental period. The experiment lasted for 14 days, and blood and fecal samples were collected at the end of the trial. Supplementation with differing amounts of ZnO did not influence the growth performance or incidence of diarrhea of the calves (P > 0.05). However, the concentrations of fecal zinc and iron linearly increased with the amount of ZnO supplementation (P < 0.01). Compared with the control group, fecal zinc content was greater when calves were supplemented with zinc at concentrations of 40 and 120 mg/d, but the iron content was greater in the Zn-120 group than in the other four groups (P < 0.05). The amount of zinc supplementation did not affect the serum concentrations of micronutrients, including calcium, copper, iron, magnesium and phosphorus, in the newborn calves (P > 0.05). While the serum zinc concentration increased quadratically as the amount of supplementation increased, peaking with 80 mg zinc/d supplementation (P < 0.05). Increasing doses of ZnO supplementation linearly elevated the concentrations of metallothionein and superoxide dismutase (P < 0.01), and quadratically enhanced that of alkaline phosphatase (P < 0.05), but linearly reduced that of malondialdehyde in serum (P < 0.05). This study demonstrates that dietary ZnO supplementation to yield 80 mg zinc/d improves zinc metabolism and antioxidant status of newborn calves during their early life.