Effect of a trace mineral injection at weaning on growth, antioxidant enzymes activity, and immune system in Nellore calves

The objective of this study was to evaluate the effects of injectable trace minerals (ITM) at the time of weaning on growth, antioxidant, and immune response of Nellore (Bos indicus) calves. Weaned calves (n = 159; 213 +/- 32 kg) were stratified by body weight (BW) and randomly assigned to 1 of 2 treatments: injection (1 mL/45 kg of BW) of saline or ITM. Saline solution consisted of 0.9% NaCl, whereas ITM had 60, 10, 5, and 15 mg/mL of Zn, Mn, Se, and Cu, respectively. The application of ITM increased (P <= 0.04) the plasma concentrations of superoxide dismutase on day 7 and plasma glutathione peroxidase on day 7 and day 21. The ITM calves had greater leukocyte concentration on day 64 (P = 0.04), whereas neutrophil and mast cell concentrations did not differ (P >= 0.67) between treatments. The ITM calves tended (P <= 0.08) to have greater concentrations of lymphocytes on day 64 and eosinophils on day 21, but not (P >= 0.15) monocytes, erythrocytes, hemoglobin, hematocrit, mean corpuscular volume, and mean corpuscular hemoglobin compared to saline calves. The ITM calves had less mean corpuscular hemoglobin concentration (MCHC; P = 0.02) and tended to have increased platelet concentrations on day 21 (P = 0.08). Growth performance did not differ between treatments (P >= 0.78). Thus, ITM at weaning did not impact growth performance, but increased plasma concentrations of antioxidant enzymes and blood platelets, improved components of the immune system, and reduced MCHC of Nellore calves.