Evaluation of Revalor-XH for Beef Heifers Fed Different Days on Feed

The objective of this study was to determine the effects of two implant strategies compared to non-implanted heifers fed varying days on feed. Calf-fed heifers (n=720; initial BW=278, SD=25 kg) were utilized in a 3 x 4 factorial design and assigned randomly to pens, and pens assigned randomly to one of twelve treatments consisting of three implant treatments and four serial harvest groups. Implant strategies included a non-implanted control (CON), a re-implant strategy using an initial implant of Revalor-200 (Merck Animal Health, Madison, NJ) followed by Revalor-200 on day 100 (REV-200), or Revalor-XH on day 0 (REV-XH). Each implant provided 200 mg trenbolone acetate and 20 mg estradiol. Serial harvest groups consisted of heifers fed 151, 165, 179, or 193 days on feed (DOF). There were no (P ≥ 0.26) implant x serial harvest interactions for carcass-adjusted performance and carcass characteristics. Dry matter intake was not different among implant treatments or serial harvest groups (P ≥ 0.11 and P = 0.72, respectively). Carcass adjusted-final BW increased linearly (P < 0.01), while carcass-adjusted ADG and G:F tended to decrease linearly (P = 0.10) as DOF increased. There was no difference in dressing percentage (P = 0.49) as DOF increased and LM area tended to increase linearly as DOF increased (P = 0.09). Fat depth, marbling score and calculated yield grade increased linearly (P < 0.01) as DOF increased. Heifers implanted with REV-200 or REV-XH had greater (P ≤ 0.05) carcass-adjusted final BW and ADG compared to CON (P < 0.01), but were not different between REV-200 and REV-XH (P ≥ 0.55). Implanted heifers were more efficient than CON heifers (P = 0.05), and REV-XH tended (P = 0.07) to be more efficient than REV-200. Implanted heifers had 12 kg greater HCW compared to CON heifers (P < 0.01). No differences were observed in fat thickness (P = 0.25) or calculated yield grade (P = 0.71) among implant treatments. Marbling score was greater (P < 0.01) for CON compared to REV-200 and REV-XH and REV-XH tended to have a greater marbling score (P = 0.10) than REV-200. No differences were observed between a new implant (Revalor-XH) and an implant strategy using Revalor-200 on day 1 and day 100. Implanting and increasing DOF substantially increase HCW and revenue but yield grade discounts increase with greater fatness due to days fed.