PSII-5 Impacts of Birth Body Weight Classification on Performance, Feed Efficiency, and Structural Characteristics in Beef Steers

Abstract

Abstract The objective was to evaluate the relationship of birth body weight (BBW) classification on performance, feed efficiency, and structural characteristics in fall-born beef steers. Steers were classified based on BBW as either light (LtBBW; < -0.5 SD from mean), average (AvgBBW; ± 0.5 SD from mean), or heavy (HvyBBW; > +0.5 SD from mean). Steers (n = 167), either Angus or Hereford sired by commercial dams, were utilized in the analysis. Steers were early weaned at 81 ± 7 days of age. Following weaning, steers were managed in drylot pens until shipping on day 1 (140 ± 6 days of age). Upon feedlot arrival, steers were randomly assigned to pens and fed a growing diet for 87 days until transitioning to a finishing diet (DM basis; 45% high moisture corn, 25% corn silage, 20% modified wet distillers grains with solubles, 10% corn-based supplement). On day 98, steers began a 56-day evaluation utilizing GrowSafe system to determine dry matter intake (DMI). Steers were weighed monthly except during the intake evaluation period, where weights were collected biweekly. Foot, leg, and claw scores were collected for structural characteristics on days 58 and 237. Hip height was collected on day 237. As designed, birth body weight differed (P < 0.01) between classifications (30, 34, and 39 kg for LtBBW, AvgBBW, and HvyBBW, respectively). The BBW classification influenced (P < 0.01) body weight on days 1, 29, 59, 77, 98, 112, 126, 140, 154, 182, and 237; HvyBBW were heavier than LtBBW and AvgBBW, which were not different from each other. During the intake evaluation period, DMI was greater (P = 0.01) for HvyBBW compared with LtBBW and AveBBW, which did not differ from each other. Similarly, ADG differed (P = 0.03) by classification; HvyBBW was greater than LtBBW, with AvgBBW being intermediate but not different from either. Consequently, gain to feed did not differ (P = 0.44) by BBW classification. Following the intake evaluation, ADG tended (P = 0.09) to differ from day 154 to 237. Overall ADG from day 1 to day 237 differed (P = 0.01) by BBW classification; LtBBW were least and HvyBBW were greatest, with AvgBBW being intermediate but not different than either. Foot, leg, and claw scores were not different (P ≥ 0.15) by BBW classification on days 58 and 237. Hip height differed (P = 0.05) by BBW classification on day 237; HvyBBW were taller than LtBBW and AvgBBW, which did not differ from each other. In summary, heavy birth body weight steers had greater growth performance and DMI than light steers but did not differ in feed efficiency or structural characteristics.