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. Heifers were randomly assigned (May 1) to be implanted with 40 mg of trenbolone acetate plus 8 mg of estradiol (IMP; Revalor G, Merck Animal Health, Summit, NJ) or not implanted (control; CON). 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 received AI followed with clean-up bulls as part of a 25-d breeding season. Body weight was measured at the beginning and end of the trial. Pregnancy detection occurred 45 d following bull removal. During the second breeding season heifers were supplemented with 0.45 kg of a 32% CP supplement 15 d before and 15 d after placement with bulls for a 56-d breeding season. 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 versus IMP (64 vs. 46 ± 3%, respectively). Implanted heifers also had a reduced pregnancy rate in their second breeding season (P = 0.02; 93 vs. 96 ± 2%, IMP vs. CON, respectively). Implanting beef heifers with trenbolone acetate plus estradiol 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.