Abstract
Throughout the cow-calf stage, essential management practices such as weaning and vaccination introduce significant stressors that can trigger inflammatory reactions. These responses stimulate the synthesis of acute-phase proteins, leading to metabolic changes that affect nutrient utilization and growth. Specific anabolic steroid implants can alleviate the negative effects of the acute-phase response on growth performance, while trace minerals such as Zn, Mn, Se, and Cu play vital roles in growth, immune cell proliferation, and as components of antioxidant enzymes. The objective of this study was to evaluate the effects of injectable trace minerals (ITM) at weaning on growth, as well as inflammatory and immune responses, in implanted and non-implanted beef calves. Thirty-four Bos indicus-influenced beef calves [16 implanted and 18 non-implanted; body weight (BW) = 284 ± 47.1 kg] were abruptly weaned (d 0) and assigned to one of two treatments: Saline (0.9% NaCl) or ITM (60 mg of Zn/mL, 10 mg of Mn/mL, 5 mg of Se/mL, and 15 mg of Cu/mL; Multimin 90, Multimin, Fort Collins, CO, USA). All calves were vaccinated against infectious bovine rhinotracheitis (IBR), parainfluenza-3 (PI3) virus, and bovine viral diarrhea virus types 1 and 2 (BVDV-1 and BVDV-2) on d 0. Body weight and blood samples were collected on d 0, 1, 3, 7, 14, 28, and 45. Serum samples were analyzed for antibody titers against IBR, PI3, BVDV-1, and BVDV-2 on days 0, 28, and 45. Data were analyzed using a generalized linear mixed model, with BW and antibody titers as response variables and day, implant, and ITM as fixed effects. Animal ID was included as a random effect, and 2- and 3-way interactions among implant and ITM were evaluated. Results indicated a significant interaction between implant and ITM (P< 0.005) on BW, with implanted calves receiving ITM exhibiting higher BW. No treatment effects were observed for BVDV-1 titers (P >0.005). However, a significant implant × ITM interaction (P< 0.005) was found for BVDV-2 titers, with non-implanted calves receiving saline showing higher titers on days 28 and 45. PI3 and IBR titers were higher (P< 0.005) on day 28 in non-implanted calves receiving saline. In conclusion, ITM application at weaning significantly improved body weight in implanted beef calves during the pre-conditioning period, while immune responses varied depending on treatment and time.