104 Effects of nutritional management and implant strategies on growth and carcass performance of steers selected for superior marbling

Abstract

Abstract A 187-day study utilizing Angus steers (283±4.4 kg) in a 2 x 2 factorial examined the effects of diet and implant strategy on growth and carcass performance of steers selected from Iowa State’s Angus herd genetically selected for enhanced marbling. Factors included diet: finishing (63 NEg; 12% roughage; FIN) or backgrounding (57 NEg, 30% roughage) fed for first 70 days before transitioning to finishing diet (BKG) and implant strategy (IMP): single, long duration implant administered on d0 (Synovex One Feedlot, Zoetis; ONE) or a multiple, regular duration implant strategy (Synovex S on d0, Synovex Choice on d70 and d155, Zoetis; SCC) designed to match trenbolone acetate delivery of 200 mg. Steers were stratified to treatment by marbling potential and initial body weight, and fed via bunks that captured individual steer feed disappearance (n = 15 steers/treatment). Carcass ultrasound, including percent intramuscular fat (IMF), was collected on d0, 70, 155, and 187. Data were analyzed in Proc Mixed of SAS with fixed effects of diet, IMP, and interaction. Initial weight was covariate for performance data, and initial IMF was covariate for IMF analysis. Steers fed BKG had greater DMI, lower ADG, and decreased G:F (P< 0.01) during first 70 days versus FIN. Implant strategy had no effect on growth at d0-d154. From d155-d187, IMP affected ADG (P=0.01) with ONE having lesser ADG, while BKG had greater ADG than FIN. ONE had greater marbling and IMF (P=0.01) on d187 than SCC, suggesting greater IMF deposition during the final re-implant period (d155-d187) and reinforcing the importance for timing of implant administration. Regardless of IMP or diet, steers selected for enhanced marbling graded 100% Choice and higher with 65% of carcasses grading Prime, suggesting potential for using implants to increase efficiency without sacrificing carcass quality.