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Growth and reproductive performance of yearling beef heifers implanted with Revalor G in the Nebraska Sandhills
Crossbred beef heifers (n = 3,242), approximately 12 mo of age, were managed at 3 locations in the Nebraska Sandhills and randomly assigned to be implanted with Revalor G (40 mg of trenbolone acetate and 8 mg estradiol, IMP), while the control group (CON) did not receive an implant. Heifers (238 ± 2 kg) grazed native Sandhills range for the duration of the trial (164 ± 4 d). Eighty-two ± 2 d following trial initiation, heifers were synchronized for estrus and AI followed with clean-up bulls as part of a 25 d breeding season. Body weight was measured at the beginning and end of trial. Pregnancy detection occurred 45 d following bull removal at the conclusion of the summer grazing period. Implanted heifers gained more and were heavier (P < 0.05; 0.68 vs. 0.64 ± 0.01 kg/d and 347 vs. 340 ± 3 kg, IMP vs. CON, respectively) at the end of the trial. However, pregnancy rate was greater (P < 0.01) for CON vs. IMP (64 vs. 46 ± 3% respectively). Implanted heifers also had a lower pregnancy rate in their second breeding season (P = 0.02; 93 vs. 96 ± 2%, IMP vs. CON, respectively). Implanting beef heifers with Revalor G at approximately 12 mo of age increased ADG and summer BW gain; however, it decreased initial and subsequent pregnancy rate compared with heifers not implanted.
Keywords: beef heifers, fertility, growth implants