262 Evaluation of a Single Growing-Finishing Diet for Single Source, pre-Conditioned Beef Steers of Lighter (273 kg) and Heavier (356 kg) Initial Body Weight (BW)

Abstract

Abstract The objective of the study was to determine the influence that initial BW has on growth performance responses, efficiency of dietary net energy (NE) utilization, and carcass traits in feedlot steers. Crossbred Charolais steers from a single source, (n = 70; initial BW = 329 ± 72.6 kg) were used in feedlot experiment at the Ruminant Nutrition Center, in Brookings, SD, during a 209-day growing-finishing period. These steers represented the lightest and heaviest proportions of steers taken from a larger group of 265 steer calves. On d 0 and d 1 BW and hip height (HH) measurements were collected for allotment proposes, and the initial experimental BW was the average between d 0 and d 1 BW. Steers were allocated to 1 of 2 treatments: 1) lighter (276 ± 16 kg; LIW) or 2) heavier (356 ± 16 kg; HIW) initial BW and allotted to 10 pens (n = 7 steers/pen; 5 pens/treatment). Steers were fed a diet containing 16% roughage once daily. Data were analyzed as a randomized complete block design with pen as the experimental unit. Treatment was included as a fixed effect and block (location) was considered a random effect in the statistical model. The LIW steers had a greater cumulative HH change compared with HIW. Final BW and carcass-adjusted (HCW/0.625) BW were greater for HIW steers by 13.1% and 13.4% respectively (P ≤ 0.01). The HIW steers had a 14.4% greater DMI (P = 0.01) compared with LIW. Cumulative ADG was greater for HIW by 3% (P = 0.04). LIW steers had improved feed conversion (P = 0.01) by 11.3% compared with HIW. The HIW steers had greater (P < 0.05) HCW (15.5%), marbling scores (6.8%), and Yield grade (16.0%), and decreased REA/HCW (P = 0.01) by 5.9% compared with LIW. Steers from HIW tended to have greater rib fat (P = 0.09) by 15% compared with LIW. The distribution of USDA Yield grade was altered by initial BW (P = 0.04) with a shift in proportions of steers with greater numerical Yield grades for steers in HIW compared with LIW. No differences were detected (P ³ 0.22) for the distribution of Quality grade or liver abscess prevalence and severity. In conclusion, HIW steers had greater growth, but poorer feed efficiency compared with LIW steers. Steers with a HIW produced fatter carcasses with a greater amount of marbling.