106. Effects of Weaning Age in a Fall-calving System on Steer Growth Performance, Carcass Merit, and Economics.

Abstract The objective was to evaluate the effects of weaning age on steer growth, performance, carcass merit, and economics. A two-year study was conducted utilizing commercial Angus-influenced, fall-born steer calves (n = 138/year). Cow/calf pairs were stratified by dam age and BW and were allotted to 6 groups/year with 23 pairs/group. Groups were randomly assigned to 1 of 2 treatments: early wean (EW) or normal wean (NW). The EW steers were abruptly weaned at 82 ± 11 days of age (day 0) and placed in an outdoor backgrounding lot and fed a ration consisting of ground hay, corn, distillers grains, and supplement along with free choice hay. The EW steers were shipped to the University of Illinois Beef and Sheep Research Facility for finishing at 139 ± 11 days of age (day 56) and NW steers were abruptly weaned and shipped to the same facility at 208 ± 9 days of age (day 125). Steers were housed in a slatted-floor feedlot facility and transitioned to a finishing diet consisting of corn silage, modified distillers, ground corn, high moisture corn, and supplement. All steers were slaughtered at a commercial abattoir (Tyson Fresh Meats, LLC, Joslin, IL) at 413 ± 10 days of age. Economics were calculated utilizing 3-year averages of feeder calf values, yardage, feed costs, and carcass values. Data were analyzed using the MIXED and GLIMMIX procedures of SAS 9.4. There was no difference (P ≥ 0.19) in steer BW or ADG through day 56. On day 85, the EW steers had greater (P < 0.01) BW and were heavier (P ≤ 0.02) than the NW steers for the remainder of the study. The EW steers had greater (P < 0.01) ADG from day 56 to day 125. The NW steers had greater (P ≤ 0.05) ADG, DMI, and G:F from day 125 through finishing. There were no differences (P ≥ 0.44) in locomotion score distributions prior to slaughter. The EW steers had greater (P ≤ 0.04) HCW, dressing percentage, YG, 12th rib fat thickness, and marbling. There were no differences (P ≥ 0.10) in LM area or KPH. There were more (P = 0.02) NW steers that graded select but there were no differences (P ≥ 0.22) between treatments for choice, premium choice, or prime. The EW steers had greater (P < 0.02) carcass value than the NW steers ($2,867.62 vs. $2,666.45, respectively). The EW steers were more (P < 0.01) profitable than the NW steers ($715.97 vs. $421.22). In conclusion, the EW steers had heavier final BW and HCW and improved marbling, ultimately resulting in greater carcass value and more profit.