189 Selection for moderate or high growth Angus-derived steer calves and their effects on feed intake and performance metrics during a 70-day feed intake period

Improvement in feed efficiency can improve beef cattle production’s sustainability. Measurements such as residual feed intake (RFI) or residual average daily gain (RADG) are used to assess feed efficiency of an animal. The objective of this study was to determine the effects of selection of growth phenotypes has on post-weaning feed intake, performance, and feed efficiency. The sires of 239 steers were selected for moderate growth (MG; top 75th percentile) or high growth (HG; Top 1st percentile) potential. Calves were produced at the Range Cow Research Center South (Spring) and North (Fall) Units from 2022 to 2023 (n = 4 seasons) to be preconditioned for 60 d. Steers were transported to Willard Sparks Beef Research Center for an individual feed intake trial following the preconditioning phase. Calves were adapted to a high concentrate diet over 28 d and then moved to the individual intake facility (Insentec feeding system, Hokofarm Group, Marknesse, Netherlands) for training, followed by a 70-d intake assessment. Animals were randomly assigned to pens containing individual feed intake monitoring systems (6 bunks/pen; 5 animals/bunk). Once trained, animals were transitioned to the finishing diet, which signaled the first day of the intake trial. Body weights were collected on d 0, 14, 28, 42, 56, and 70 during the 70-d individual feed intake trial. Metabolic body weight and average daily gain (ADG) for each individual steer was used for RFI and RADG determination by regressing body weight (BW) on day of BW collections using the Proc REG procedure in SAS. Residual Feed Intake and RADG calculations were determined by the difference in observed values and predicted values. Proc MIXED procedure in SAS was used for continuous data, and pen served as the random effect. Moderate growth steers in the Spring 2022, Fall 2022, Spring 2023, and Fall 2023 seasons dry matter intake were 1.36, 1.14, 1.24, and 1.15 kg, respectively (P ≤ 0.01; Table 1), less than HG steers. Feed efficiencies (P ≥ 0.19) did not differ between HG or MG phenotype steers for any of the feeding groups. Moderate growth phenotype steers in Spring 2022 and 2023 tended to have a lower RFI (-0.18 and -0.44 kg, respectively; P ≤ 0.07) than the HG phenotype (0.47 and 0.22 kg, respectively), whereas in Fall 2022 and 2023, growth phenotypes did not differ (P ≤ 0.68). Residual average daily gains (P ≥ 0.11) did not differ between MG and HG within each season. Steers with the MG phenotype consumed less feed resources with lower RFI, but performance and feed efficiency during the feed intake trial did not differ. The improved RFI without impacting performance may indicate MG cattle can provide for more sustainable beef production, but more research is needed.