Effects of feeding duration, implant dose, and terminal window duration on growth performance and carcass characteristics of feedyard steers and heifers

Objective: Our objective was to evaluate effects of feeding duration (days on feed, DOF), terminal window (TW), and implant program dose on growth performance and carcass characteristics of beef steers and heifers. Materials and Methods: Heifers in Exp. 1 (n = 3,360; 351 +/- 31 kg) and Exp. 2 (n = 3,778; 310 +/- 28 kg) were used in randomized complete block designs with 3 x 2 factorial treatment arrangements. In Exp. 1, factor 1 was DOF (139, 162, and 183) and factor 2 was TW (60 or 100). In Exp. 2, factor 1 was implant program {(1) IH/H-Component TE-III with Tylan on d 0 followed by a Component TE-H with Tylan [140 mg of trenbolone acetate (TBA):14 mg of estradiol; Elanco], (2) IH/200 Component TE-IH with Tylan on d 0 followed by a Component TE-200 with Tylan, and (3) 200/200-Component TE-200 with Tylan on d 0 and at reimplant} and factor 2 was TW (60 or 100). In Exp. 3, feedlot data from an industry database (Benchmark, Elanco Knowledge Solutions, Kansas City, KS) was used in an observational study and organized by sex and implant program [steers = IS/200 (total of 280 mg of TBA and 36 mg of estradiol), XS (200 mg of TBA and 40 mg of estradiol), and 200/200 (a total dose of 400 mg of TBA and 40 to 56 mg of estradiol or estradiol benzoate); heifers = IH/200 (total of 280 mg of TBA and 28 mg of estradiol) and 200/200]. Repeated-measure and nonlinear broken-slope models were used to evaluate TW on live performance. Results and Discussion: In Exp. 1, ADG decreased (P = 0.03) and final BW, marbling score, hot carcass weight (HCW), backfat thickness, and calculated empty body fat (EBF) increased (P < 0.03) as DOF increased. In Exp. 2, greater implant program dose tended (P <= 0.10) to increase ADG and DMI and increase (P <= 0.02) G:F, HCW, DP, and LM area. Furthermore, overall dose reduced (P <= 0.03) marbling score and EBF. In Exp. 3, interactions between implant program, live performance, and TW were detected (P < 0.001). Steers given 200/200 exhibited the greatest (P < 0.05) ADG, followed by XS and IS/200 from TW 50 to 100. Inversely, steers given XS had the greatest (P < 0.05) F:G, followed by IS/200 and 200/200 from TW 50 to 90. Heifers administered 200/200 exhibited greater (P < 0.05) ADG between TW 50 to 70 and reduced (P < 0.05) F:G through TW 110 compared with IH/200. Conclusions and Applications: Increased DOF resulted in reduced ADG and increased HCW and EBF. Increased implant dose improved live performance and HCW. There is a finite number of TW days before growth suffers from inadequate stimuli. Furthermore, cattle type, implant program dose, DOF, and TW all require consideration when designing implant programs.