Effect of Lighter and Heavier Initial Weight on Growth Performance and Carcass Traits of Single-Source Beef Steers.

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. Charolais×Red Angus steers ( n = 70) selected from a larger single-source group were used in a 209-d growing-finishing feedlot experiment. Steers were assigned to two groups based on initial BW (light initial weight, LIW = 273 ± 16.0 kg; heavy initial weight, HIW = 356 ± 14.2 kg) and allotted into 10 pens ( n = 7 steers per pen; 5 pens per experimental group) the within pen standard deviation for LIW was from 14.1 kg to 20.9 kg and for HIW was from 13.7 kg to 16.0 kg. Steers were fed a common diet once daily. Experimental data were analyzed as a randomized complete block design with pen as the experimental unit. LIW steers had a greater cumulative HH change ( p = 0.04). A treatment × day interaction ( p = 0.05) was observed for HH with HIW steers having a greater HH at all time points. Final BW and carcass-adjusted (HCW/0.625) BW were greater for HIW steers by 13.1% and 13.4% respectively ( p ≤ 0.01). HIW steers had a greater DMI ( p = 0.01) compared to LIW. Cumulative ADG was greater for HIW by 3% ( p = 0.04). LIW steers had better feed conversion ( p = 0.01). HIW steers had greater ( p ≤ 0.05) HCW, marbling scores, and yield grade (YG), with decreased REA/HCW ( p = 0.01) compared to LIW. The distribution of USDA Yield Grade was altered by initial BW ( p = 0.04). No differences were detected ( p ≥ 0.22) for the distribution of Quality grade nor liver abscess prevalence and severity. Regression coefficients did not differ between LIW and HIW for urea space calculations of empty body water, fat, or protein ( p ≥ 0.70). A quadratic response was noted for empty body fat (EBF), empty body water (EBH20), and carcass protein (CP). In conclusion, HIW steers had greater growth, but poorer feed efficiency compared to LIW steers. Steers with a HIW produced fatter carcasses with a greater degree of marbling.