LAUSR

Yearling beef heifers (n = 6,239) were used in a randomized complete block design experiment to evaluate the effects of long-acting implants on feedlot growth performance and carcass characteristics when compared with re-implant programs. Heifers (initial BW = 324 kg, SEM = 0.85) were randomized to 1 of 4 implant treatments with 12 pens/treatment: 1) Revalor-IH (80 mg trenbolone acetate [TBA], 8 mg estradiol [E]) at initial processing followed by a Revalor-200 (200 mg TBA, 20 mg E) 90 d later (IH/200); 2) Revalor-200 at initial processing followed by a Revalor-200 90 d later (200/200); 3) Revalor-XH (200 mg TBA, 20 mg E) at initial processing (XH); and 4) Synovex One Feedlot (200 mg TBA, 20 mg E) at initial processing (ONE). Revalor-XH and Synovex One are long-acting implants designed to extend hormone release, eliminating the need to re-implant cattle. After initial processing, XH and ONE heifers were not removed from their pens until harvest. Final BW (556 kg), DMI (7.95 kg/d), ADG (1.26 kg), and feed efficiency (0.158) did not differ (P > 0.23) among treatments. Hot carcass weight (HCW) was greater (P < 0.10) for 200/200 (364 kg) than XH (361 kg) and ONE (360 kg), with no other differences (P > 0.10) in HCW among treatments. Dressing percentage (DP) and longissimus muscle (LM) area were greater (P < 0.01) for 200/200 than all other treatments, and greater for IH/200 than XH and ONE. Marbling score was reduced and average yield grade (YG) was improved (P < 0.01) for 200/200 vs. all other treatments and for IH/200 vs. XH and ONE. Compared with re-implant programs, long-acting implants decreased DP and LM area, increased marbling score and YG, and did not differ in final BW. The Revalor-200/200 re-implant program resulted in improved HCW when compared with long-acting implants.