Effects of trace mineral injection at weaning on growth, inflammatory and immune responses in Bos indicus-influenced beef steers with or without growth-promoting implants.

Management interventions during a calf's life can enhance growth performance and support immune function during challenging periods, ultimately impacting productivity. Bos indicus-influenced beef steers (n = 34; 92.4 ± 6.08 kg) were randomly assigned to receive either no implant (NIP) or a 43.9 mg estradiol implant (IP) at 60 days of age (d - 180) to evaluate the effects on growth performance until weaning (d 0). At weaning (d 0), calves were further assigned to receive either an injectable trace mineral (ITM; 60 mg Zn/mL, 15 mg Cu/mL, 5 mg Se/mL, and 10 mg Mn/mL) or saline (S; 0.9% NaCl), resulting in four treatment groups: NIP + S (n = 8), NIP + ITM (n = 8), IP + S (n = 9), and IP + ITM (n = 9). Saline and ITM were administered subcutaneously at a dose of 1 mL/45 kg of BW. On d 0, all calves were vaccinated against bovine viral diarrhea virus type 1 and 2 (BVDV-1 and 2), bovine respiratory syncytial virus (BRSV), parainfluenza-3 (PI3), and infectious bovine rhinotracheitis (IBR). Body weights were collected on d - 180, -135, -80, -40, 0, 1, 3, 7, 14, 28, and 45. Blood samples were collected on d 0, 1, 3, 7, 14, 28, and 45 for analysis of insulin like growth factor hormone (IGF-1), cortisol, haptoglobin (Hp), ceruloplasmin (Cp), and for antibody titers against IBR, PI3, BVDV-1, and BVDV-2. Implant administration tended to increase BW at weaning (P = 0.10), with IP steers being 16.4 kg heavier than NIP steers at weaning. After weaning, steers in the IP + ITM group showed a tendency for increased BW (P = 0.08). Administration of ITM at weaning induced an inflammatory response, as indicated by greater concentrations of Hp, and Cp on d 3 and d 7, respectively (P < 0.05). Serum titers against IBR and BDVD-2 were greater in calves that received ITM (P = 0.01), indicating an enhanced immune response. In summary, implant administration increased steer BW during the suckling phase, and ITM may enhance this effect during the post-weaning period. While ITM elicited an inflammatory response, it also improved the humoral immune response to IBR vaccination.