Effect of Growth-Promoting Implants and Revaccination Timing on Stress Physiology and Growth Performance in Male Beef Calves

Abstract Hormonal growth-promoting implants are known to enhance growth performance in beef cattle, but their influence on vaccine response has not been studied extensively. Herein, we evaluated the growth performance and immunity of beef steers under different hormonal implant treatments and timing of booster vaccination. Fifty-nine crossbred beef calves were stratified by body weight (BW) and age (109 ± 18.9 kg and 70 ± 8 d of age) and randomly distributed into a completely randomized design with a 3 × 2 factorial arrangement to one of three implant treatments: 1) no implant (CON); 2) short-term payout period implant (Synovex C; ST); or 3) long-term payout period implant (Synovex One Grower; LT), and to one of the booster vaccination groups; at weaning (WV) or 7 days post-weaning (PWV). From implantation, and initial vaccination (d 0) until weaning (d 114), calves were raised with their dams in a single pasture. After weaning, calves were allocated to a single pen until d 63 post-weaning (d 177). Body weight was recorded, and blood samples were collected to analyze insulin-like growth factor, cortisol, β-hydroxybutyric acid, non-esterified fatty acids, leptin, serum antibody titers, and complete blood cell count. Peripheral blood lymphocyte concentration was greater in CON compared with ST and LT (P < 0.01), and greater plasma leptin (P = 0.01) in ST compared to LT, while CON was intermediate. A treatment × timing of booster vaccination (P < 0.01) was observed with greater peripheral blood monocyte counts in LT-PWV compared to ST-PWV and CON-PWV. A timing of booster vaccination × day interaction (P = 0.01) was observed for plasma cortisol with smaller concentration in WV compared with PWV at booster vaccination and d 28 post-booster vaccination. No main effects of treatments or treatment interactions were observed for serum antibody titers (P > 0.20). Implant treatment did not affect weaning weights; however, calves implanted with LT were the heaviest on d 142 (P = 0.03) and tended to have greater final body weights at the end of the study (P = 0.07). In summary, implant strategy and booster vaccination timing affected metabolic and immune parameters in beef calves but did not influence serum antibody titers. Growth performance was not affected at weaning; however, long-term-implanted calves were heavier post-weaning and tended to have greater final BW, indicating improved growth without compromising antibody-mediated immune responses.