454 Effect of Revalor-XH Compared with Revalor-IH Followed By Revalor-200 on Feedlot Performance and Carcass Characteristics of Heifers Fed to Three Different Endpoints

Abstract Crossbred heifers (n = 3,780; initial BW = 309 ± 55 kg) were utilized in a serial harvest experiment to compare the effects of two growth-promoting implant programs on feedlot performance and carcass characteristics. A traditional heifer re-implant program consisting of a Revalor-IH (80 mg trenbolone acetate [TBA] and 8 mg estradiol) at experiment initiation followed by a Revalor-200 (200 mg TBA, 20 mg estradiol) on day 90 was compared with a single Revalor-XH at experiment initiation. Revalor-XH contains 200 mg TBA and 20 mg estradiol in a proprietary coated extended-release formulation, with 4 uncoated pellets consisting of 80 mg TBA and 8 mg estradiol, and 6 coated pellets consisting of 120 mg TBA and 12 mg estradiol. Heifers were harvested after 172, 193, and 214 days-on-feed (DOF) resulting in a 2 x 3 factorial arrangement of treatments (2 implant treatments, 3 serial harvest groups). Heifers were assigned randomly into 54 pens with 70 heifers/pen, resulting in 9 replications/treatment. Revalor-XH heifers were not removed from their pens during the experiment. There were no implant treatment x serial harvest interactions (P > 0.05) for carcass-adjusted performance or carcass characteristics. Increasing DOF resulted in a linear increase (P < 0.03) in carcass-adjusted final BW, HCW, dressing percentage, and percent USDA Prime and Choice carcasses, and a linear decrease (P ≤ 0.01) in ADG, DMI, G:F, and percent USDA Select carcasses. Percentage of heifers reaching USDA yield grade 4 and 5 increased (P ≤ 0.01) with increasing DOF. Based on changes in live BW and HCW as DOF progressed, the proportion of live BW gain captured as HCW (carcass transfer) was 80%. Carcass-adjusted final BW (P = 0.06) and HCW (P = 0.09) tended to be greater for Revalor-IH/200 heifers than for Revalor-XH heifers. Dry matter intake tended (P = 0.06) to be greater, and ADG (P = 0.03) and G:F (P < 0.01) were lower for Revalor-XH heifers than for Revalor-IH/200 heifers. Dressing percentage (P = 0.21) and USDA quality grade distribution (P > 0.16) were not affected by implant treatment. Revalor-XH heifers produced more (P < 0.01) USDA Yield Grade 4 and 5 carcasses than Revalor-IH/200 heifers, with no differences (P > 0.15) in USDA Yield Grade 1, 2, or 3 carcasses. Compared to a Revalor-IH/200 implant strategy, heifers implanted with Revalor-XH had 1.2% lower ADG and 2.0% lower G:F while producing similar USDA quality grades. These data indicate that utilizing Revalor-XH is a v