Production, Management and the Environment: Beef 2

Data from 82 studies (60 steer and 22 heifer studies) were compiled and analyzed to evaluate the effects of anabolic implants on feedlot performance and carcass traits. Dependent variables in the model included ADG, G:F, DMI, dressing percentage, HCW, and marbling score. Categories created for type and dosage of active compound were: low dose primarily estrogenic hormone (E2; LOW), moderate dose E2 (MOD), intermediate dosage combination E2 + trenbolone acetate (TBA; INT), and full-strength TBA or E2 + TBA (HIGH). Treatment categories were: no implant, single MOD, single HIGH, delayed HIGH, initial and terminal MOD, initial and terminal INT, initial LOW and terminal HIGH, initial MOD and terminal HIGH, initial INT and terminal HIGH, and initial and terminal HIGH. Implant treatment was the fixed effect in the model, and trial was a random effect. Increasing the implant dosage (potency of individual implants or reimplant vs. single implant) increased ADG, G:F, and HCW in both steers and heifers (P < 0.01). Increasing implant dosage in steers decreased marbling score (P < 0.01) but did not affect yield grade (P = 0.11). Increasing implant dosage in heifers decreased yield grade and marbling score (P < 0.01) so that when marbling score was adjusted to a common yield grade, there was no effect of implant on marbling score (P = 0.52). The percentage of Prime and Choice carcasses increased at a decreasing rate with increased marbling score, fitting the equation: Percent Prime + Choice = (sin[-2.2144 + 0.00548 * Marbling score]) * 100; (R2 = 0.86). Implants reduce marbling content of steers, but high-potency implant programs will have a decreasing impact on quality grade in cattle with high average marbling score compared with cattle with low average marbling score.