Effect of single implant and re-implant strategies on growth performance and carcass characteristics in finishing cattle.

Three randomized complete block design experiments evaluated a single implant strategy versus approved re-implant strategies in feedlot cattle using trenbolone acetate (TBA) and estradiol-based implants. Revalor implants were from Merck Animal Health; Synovex implants were from Zoetis. Exp. 1: A total of 1400 steers (initial BW = 320 kg), housed in open lot, dirt-surfaced pens with a concrete apron, were assigned to either a single Revalor-XS (initial 80 mg TBA + 16 mg E2; delayed 120 mg TBA + 24 mg E2) administered 209 d pre-harvest (XS) or a re-implant strategy of Synovex-Choice (100 mg TBA + 14 mg EB) on d 0 followed by Synovex-ONE Feedlot (200 mg TBA + 28 mg EB) 60 d later (CHSOF). Pen served as the experimental unit. Initial BW differed and was included as a covariate. CHSOF increased (P = 0.01) DMI, and numerically increased ADG and HCW relative to XS, XS numerically improved net energy utilization by 2.27% (P ≤ 0.12). Exp. 2: Steers (n = 480; initial BW = 388 kg) were assigned to 48 open lot, dirt-surfaced pens with a concrete apron (10 steers/pen). A 2 × 3 factorial compared XS vs. CHSOF (re-implant at 70 d) across harvest times of 162, 183, or 204 DOF. Pen served as the experimental unit. Implant strategy had minimal effect on performance and carcass traits; increasing DOF increased (P ≤ 0.01) HCW, rib fat, and ribeye area. Exp. 3: Beef × Dairy heifers, (n = 685) and steers (n = 660; initial BW ≈ 167-170 kg) received CHSOF (d 100 and 200), CHPLUS (Choice d 200, Synovex Plus d 300), or Revalor strategies: XS (steers) or XH (heifers; lower estradiol dose) at d 100 (RevX100) or d 200 (RevX200). Cattle were hosued in open lot, dirt-surfaced pens with a concrete apron. Individual animal served as the experimental unit. RevX100 and RevX200 produced heavier (P ≤ 0.01) HCW than CHPLUS, while CHPLUS improved (P ≤ 0.01) yield grade. In conclusion, a single extended-release implant (Revalor-XS/XH) performs comparably to Synovex re-implant programs in cattle finished over 200 to 400 DOF.