274 Effects of Revalor ih/revalor-200 Re-implant Program or Revalor-xh on Performance and Carcass Characteristics of Finishing Heifers Fed for 179, 200, or 221 Days

Abstract

The objective of this study was to compare feedlot performance and carcass traits between two implant programs in heifers harvested at 3 different days on feed (DOF; 179, 200, or 221 d). Crossbred beef heifers (n = 3,084; 291 + 3.9 kg) were used in a 2×3 factorial arrangement of treatments in a randomized complete block design. Revalor-IH (80 mg TBA and 8 mg E₂) was administered on arrival followed by Revalor-200 (200 mg TBA and 20 mg E₂) 94 d before harvest (IH/200) or Revalor-XH (80 mg TBA and 8 mg E₂, uncoated; 120 mg TBA and 12 mg E₂, coated) was administered on arrival (XH). No implant × DOF interaction was detected (P ≥ 0.09) for any parameter. Heifers subjected to IH/200 had greater (P ≤ 0.01) final BW, ADG (P < 0.01) and G:F (P = 0.01). As DOF increased, BW increased (P ≤ 0.01) while ADG (P<0.01) and G:F (P ≤ 0.01) decreased. Hot carcass weight was greater (P = 0.01) for IH/200 compared with XH (367 vs. 361 kg, respectively). Heifers receiving XH had greater marbling scores (P = 0.02; 582 vs. 568) and BF (P = 0.01; 1.78 vs 1.70 cm) compared with IH/200 while re-implanted heifers had increased (P = 0.01) REA (86.5 vs. 83.2 cm²). Heifers implanted with XH tended to be fatter than those implanted with IH/200 having a greater (P = 0.01) proportion of USDA Prime and fewer (P<0.01) USDA Select. Increasing DOF increased (P ≤ 0.03) HCW, DP, BF, REA, marbling, and proportion of USDA Prime carcasses. Growth performance and HCW were increased for IH/200 compared with XH heifers. Increasing DOF resulted in poorer ADG and G:F but increased HCW.