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101 Effects of traditional growth-promoting re-implant or long-acting implant programs on growth performance and carcass characteristics of heifers fed for 221 days


 Beef heifers (n=1478) were used in a randomized complete block design to compare the effects of a traditional re-implant (Revalor-IH/Revalor-200) or a long-acting implant program (Revalor-XH) on feed yard growth performance and carcass characteristics. Heifers (initial BW = 263 kg; SD = 3.44 kg) were randomized to 1 of 20 pens with pens randomly assigned to Revalor-IH (80 mg trenbolone acetate [TBA], 8 mg estradiol [E]) at initial processing followed by Revalor-200 (200 mg TBA, 20 mg E; Rev-IH/200) 103 days later or Revalor-XH (200 mg TBA, 20 mg E; Rev-XH) implant treatments. Heifers were on feed for an average of 221 d with Rev-XH heifers remaining in their pens for the duration of the study. Final BW (559 kg) and feed efficiency (0.175) did not differ (P > 0.11) between treatments. Dry matter intake was greater (P < 0.10) for Rev-IH/200 (7.70 kg) compared with Rev-XH (7.60 kg) heifers causing greater (P < 0.10) ADG for Rev-IH/200 (1.35 kg) versus Rev-XH (1.33 kg). Heifers implanted with Rev-IH/200 (365 kg) had greater (P < 0.10) HCW than those implanted with Rev-XH (361 kg). However, differences in dressing percentage were not detected (P > 0.15). Longissimus muscle area was greater (P < 0.05) for heifers implanted with Rev-IH/200 (89.55 cm2) versus those implanted with Rev-XH (87.87 cm2). Back fat thickness (1.76 cm), calculated yield grade (3.28) and marbling score (487) did not differ (P > 0.42) due to implant treatment. Differences resulting from implant treatment in the percentage of carcasses within USDA Quality Grades (P > 0.34) and USDA Yield Grades (P > 0.18) were not observed. Heifers that were re-implanted had improved ADG, DMI and HCW compared with those receiving a long-acting implant with minimal effects on carcass characteristics.