173 New Revalor Implant Comparisons for Finishing Heifers

Abstract The objective of this study was to evaluate new implant strategies on performance and carcass characteristics of feedlot heifers compared to non-implanted heifers. Crossbred heifers (n=500; initial BW= 280 kg, SD= 21 kg) were utilized in generalized randomized block design with 2 initiation times and BW blocks within start, and assigned randomly to pens within block. Pens were assigned randomly to one of 5 treatments. Treatments included heifers not implanted or given a Revalor (Merck Animal Health, De Soto, KS) implant. Implant treatments consisted of Revalor-XR on day 1, Revalor-XH on day 1, Revalor-200 on day 1, or Revalor-200 on day 70. All implants provided 200 mg of trenbolone acetate (TBA) and 20 mg estradiol (E2) but timing of release varies across implant treatments. Heifers were fed for 198 days. There were no differences in DMI (P = 0.22) between all treatments. Implanted cattle had heavier carcass-adjusted final BW (P < 0.01), but there was no difference in BW between implanted treatments (P > 0.87). All implanted cattle had greater ADG compared to control cattle (P = 0.03), which resulted in an improvement in carcass-adjusted G:F (P < 0.01). Implanted heifers had greater HCW (P < 0.01) and lower marbling scores (P < 0.01) compared to non-implanted heifers, but there were no differences in HCW, dressing percentage, fat thickness, or marbling score among implant treatments (P > 0.38). Non-implanted cattle had lower dressing percentage and greater marbling scores compared to implanted heifers (P ≤ 0.04). Revalor-XH, Revalor-XR, and Revalor-200 day 70 treatments increased LM area (P < 0.01) compared to Revalor-200 on day 1 or non-implanted heifers, which translated into a lower calculated yield grade (P = 0.04). Distribution of quality grade (P = 0.07) and yield grade (P = 0.10) between implanted and non-implanted heifers varied. During the first 70 days of the feeding period, Revalor-XH and Revalor-200 on day 1 treatments had greater ADG and G:F (P < 0.01) compared to the other implant treatments and control heifers. From days 70 to 140, heifers implanted with Revalor-XR or Revalor-200 on day 70 had greater ADG and G:F (P < 0.01) compared to the other treatments. Until day 175, all implanted cattle were heavier than the control (P < 0.01). Implanting heifers improved ADG, G:F, and HCW compared to non-implanted heifers. While interim performance varied, the timing of release did not affect heifer performance over the entire 198 days.