Effect of dietary micronutrient supplementation on growth and reproductive parameters in bull calves

Optimal nutrition during early growth is crucial for enhancing calves' development and future productivity. This study evaluated the impact of supra-nutritional supplementation of specific micronutrients on growth, antioxidant status, immunity, and reproductive parameters in Sahiwal bull calves. Eighteen male calves (6 months old) were randomly assigned to three groups (n = 6): T1 (basal diet), T2 (25 % higher Zn, Mn, Vit. A & E than in the basal diet), and T3 (50 % higher than in the basal diet). The trial lasted for 180 days. No significant differences (P > 0.05) were observed among groups for body weight, morphometric measurements, average daily gain (0.54-0.57 kg/day), dry matter intake, nutrient digestibility, or nitrogen balance. Hematological and most biochemical parameters (Haemoglobin: 9.6-10.2 g/dL, Red Blood Cells, White Blood Cells, glucose, total protein, albumin, globulin) remained unaffected. However, alkaline phosphatase activity increased significantly in T2 (88.3 IU/L) and T3 (93.6 IU/L) compared to T1 (74.5 IU/L) (P < 0.01). Supplementation improved (P < 0.01) antioxidant status: superoxide dismutase activity increased by 18-22 %, and ferric Reducing Antioxidant Power by 15-19 % in T2 and T3. Total immunoglobulin levels were higher (P < 0.05) in the supplemented groups (T2: 2.87 mg/mL; T3: 2.95 mg/mL) compared to the control (T1: 2.61 mg/mL). Plasma mineral levels of zinc and manganese and vitamin A and E concentrations increased significantly (P < 0.05) in T2 and T3. Notably, testosterone levels rose significantly after four months (T1: 1.42 ng/mL; T2: 1.62 ng/mL; T3: 1.67 ng/mL; P < 0.05), indicating potential for earlier puberty onset. Scrotal circumference and testicular temperature gradient measured by infrared thermography were similar (P > 0.05) among the groups. In conclusion, dietary supplementation with Zn, Mn, vitamin A, and E at 25 % above basal levels enhances antioxidant status, immune response, and testosterone production in bull calves without affecting growth performance, supporting earlier reproductive maturity.