272 Managing for Efficiency and Quality Through Diet and Implant Strategies on Steers Selected for Superior Marbling

Abstract A 144-day study assessed the effects of dietary energy and implant potency to determine optimum strategies for managing feed conversion (F:G) and marbling. Fifty-four Angus steers (327 ± 8 kg) from Iowa State University’s herd genetically selected for enhanced marbling were stratified by initial bodyweight (BW), ultrasound intramuscular fat, and age to a 2 × 3 factorial. Dietary treatments included: low energy (1.30 Mcal NEg/kg DM, 18% roughage level; LE) or high energy finishing ration (1.39 Mcal NEg/kg DM, 8% roughage; HE). Implant treatments (IMP; Merck) included: no implant (NOIMP), Revalor-IS (RIS), or Revalor-200 (R200) on d 0 and 74. Steers were fed via bunks capturing daily individual feed disappearance (n = 9 steers/treatment). Steers were weighed on d 0, 74, and 144 and harvested on d 145. Data were analyzed in Proc Mixed of SAS with fixed effects of diet, IMP, and interaction. No interactions were observed for feedlot performance (P > 0.17). Steers fed HE had greater average daily gain (ADG) and final BW than LE steers (P < 0.01) while LE steers had greater F:G (P = 0.04). Final BW and ADG were greatest for R200, intermediate for RIS, and lowest for NOIMP (P < 0.01). F:G was greatest for NOIMP, intermediate for RIS, and lowest for R200 (P < 0.01). Steers fed HE had increased ribeye area (P < 0.01) and tended to have greater marbling score (P = 0.06; 809) than LE steers (769). While ribeye area increased in response to implant potency (P < 0.01), marbling score was not impacted (P = 0.21) by IMP (815, 771, 782, for NOIMP, RIS, R200, respectively). Overall, steers graded 100% Choice or higher and 55% Prime. These data suggest implants, when used appropriately, improve growth performance and efficiency in beef steers without compromising carcass quality.