Effect of growth implant regimen on health, performance, and immunity of high-risk, newly received stocker cattle.

Growth implant efficacy may be affected when administered to nutritionally stressed calves, whereas the procedure may alter health or the humoral immune response to respiratory vaccination. The study objective was to determine the effect of different administration times (d 0, 14, or 28) of a growth implant containing 200 mg progesterone and 20 mg estradiol benzoate on health, performance, and metabolic and immunologic variables in high-risk, newly received beef calves used in a 120-d receiving/grazing stocker system. Crossbred bull and steer calves ( = 203) were weighed (initial BW = 203 ± 2.7 kg), stratified by castrate status on arrival, and randomly assigned to experimental treatments consisting of 1) negative control (no growth implant administered), 2) growth implant administered on d 0, 3) growth implant administered on d 14, and 4) growth implant administered on d 28. There were no differences ( ≥ 0.16) in BW or ADG during the 42-d receiving period. However, ADG during the subsequent grazing period and overall was greater ( ≤ 0.01) for implanted calves versus the negative control. Growth implant timing did not affect the rate of clinical bovine respiratory disease morbidity ( = 0.52; 94% morbidity overall) or bovine viral diarrhea virus type 1a antibody titer concentration ( = 0.61). Indicative of an overall negative energy balance on arrival, NEFA decreased sharply subsequent to d 0 (day effect, < 0.001), but was not affected ( = 0.47) by the timing of growth implantation. Blood urea N concentrations increased transiently (day effect, < 0.001); however, no treatment effect was observed ( = 0.72). Therefore, under conditions of this study, the timing of growth implant administration did not affect growth implant efficacy, health, or metabolic or immunologic variables in newly received, high-risk beef stocker calves. Overall, our observations suggest that there is not a clear benefit to delaying growth implantation and that a growth implant does not affect health or vaccine response in newly received beef calves.