Influence of timing of growth implant administration on performance and health of newly received beef cattle1,2

A total of 442 Angus and crossbred steers (initial BW = 243 ± 13.1 kg) were used in a randomized complete block design to evaluate the effect of implant timing on performance and health of newly received steers. Treatments included administration of a growth implant (Revalor-XS; Merck Animal Health, Summit, NJ) on d 0 of the experiment (ARR) or d 28 (DEL). On d 0, 5 steers from each pen were injected with ovalbumin (OVA) to evaluate a primary humoral immune response. On d 28, the same 5 steers received a secondary OVA injection, and 5 additional steers from each pen received a single OVA injection. Final BW (P = 0.02) and ADG d 0 through slaughter (P = 0.03) were greater for DEL compared with ARR (BW: 636 vs. 627 ± 8.3 kg; ADG: 1.78 vs. 1.74 kg ± 0.029, respectively). Steers implanted on arrival had greater DMI (P ≤ 0.02) d 0 to 28, d 29 to 56, and d 57 to 112 and lower (P ≤ 0.03) G:F d 57 to 112, d 113 to 169, d 170 to slaughter, and d 0 to slaughter (0.175 vs. 0.186 ± 0.003) when compared with DEL steers. On a pen mean basis, BW at d 28 and ADG d 0 to 28 were numerically higher (P = 0.25) for ARR steers as compared with DEL steers (294 vs. 291 ± 1.8 kg and 1.80 vs. 1.71 ±  kg, respectively). Hot carcass weight was numerically greater (P = 0.16) for DEL compared with ARR steers (383 vs. 378 ± 3.6 kg, respectively). Steers implanted on arrival tended (P < 0.07) to have greater OVA IgG concentration after OVA administration. These results suggest that delaying the time of growth implant administration of newly received cattle had minimal effects on animal performance, health, and immune response. The observed improvements in feedlot performance from d 0 through slaughter that were observed for the DEL versus ARR steers were likely due to timing of slaughter relative to depletion of implant active ingredients.