95 Effects of Three Implant Programs on Growth Performance, Carcass Outcomes, and Weekly Activity Minutes of Finishing Steers Fed Different Days on Feed

Abstract This study evaluated the effects of a single slow-release implant compared to two re-implant programs administered at either 120 days on feed (DOF) or 80 days from harvest on performance, carcass characteristics, and activity of serially harvested feedlot cattle. Using a randomized complete block design, steers (n = 4,680) were randomly assigned to 72 pens and 1 of 12 treatments in a 3 × 4 factorial arrangement. Treatments were either a slow-release implant (SR), an initial slow-release implant followed by re-implant at 120 DOF (SR+RI-120), or an initial slow-release implant followed by re-implant 80 days from harvest (SR+RI-80) administered to cattle harvested at 166, 180, 194, or 208 DOF. A 3-axis accelerometer ear-tag was used in a subset (n =1,080) of animals to quantify rumination time and activity. No interactions (P ≥ 0.09) were observed for implant × DOF. Implant did not affect (P ≥ 0.25) final BW, ADG, or DMI, but re-implanted steers had a greater (P < 0.01) G:F ratio than SR. Re-implanted steers also had greater (P ≤ 0.03) HCW, dressed yield, and ribeye area, but less (P < 0.01) backfat, marbling, and empty body fat (EBF) compared to SR. Re-implanted steers had less (P < 0.01) choice and yield grade 4 and 5 carcasses than SR steers. As DOF increased, HCW, dressed yield, backfat, marbling, and EBF increased linearly (P < 0.01). The percentage of choice and yield grade 4 and 5 carcasses also increased (P < 0.01) linearly with additional DOF. An implant × day effect (P < 0.01) for weekly activity minutes suggests re-implanted steers had greater activity after re-implant administration. Re-implanting within the payout period of a slow-release implant increases feed efficiency, HCW, dressed yield, and activity minutes, but decreases carcass fatness and reduces quality grade regardless of timing of secondary implant administration.