LAUSR

Abstract: The effect of residual feed intake adjusted for backfat thickness (RFIfat) on heifer pregnancy rate and subsequent lifetime productivity was examined in 867 beef females that were ranked as low, medium, or high RFIfat. Age at first calving, weaning weight of first calf, and most probable producing ability for birth weight (MPPAbw) and weaning weight (MPPAww) were calculated to assess first parity heifer productivity. The effect of heifer RFI adjusted for backfat (RFIfat; n = 532) on subsequent lifetime cow productivity (n = 415) was calculated based on kg of calf weaned per cow bred per year. A total lifetime productivity measure (n = 218) were also calculated as total calf weaning weight (kg) output per cow culled. RFI rank had no significant effect on pregnancy rate, when adjusted for season and site differences (P = 0.33). No significant correlations (P < 0.05) were observed between MPPAww and RFI, RFIfat, RFI adjusted for backfat and feeding event frequency (RFIfat & activity), or age at first calving. A negative trend (P < 0.10) between RFI, RFIfat, and MPPAbw calculated from first parity pregnancy rate and production traits was no longer apparent when adjusted for RFIfat & activity. These results suggest that selection for low RFI replacement heifers has no impact on their first parity pregnancy rate and productivity or on subsequent cow productivity.