Selection for low birth weight and high yearling weight in angus beef cattle

Abstract

Angus bulls were chosen for either high birth weight (BW), high yearling weight (YW), or low BW, high YW using Expected Progeny Difference (EPD) estimates for proven sires. The high group had birth weight EPD ⩾ 3.0 kg and yearling weight EPD ⩾ 20 kg while the low group had birth weight EPD ⩽ 1.5 kg and yearling weight EPD ⩾ 20 kg. The selected sires were randomly mated to registered Angus cows over 4 years and resulting progeny data were analyzed for BW, weaning weight, post-weaning gain, YW, gestation length and yearling pelvic measurements. High group least squares means (LSM) for BW exceeded the low group by 3.8 kg ( P < 0.01). No significant group differences ( P > 0.10) were seen for weaning weights, post-weaning gain or yearling weights although actual LSM were in close agreement with sire EPD differences between groups. Yearling weight LSM differed by 6.6 kg compared with a 6.3 kg difference between high and low groups for sire yearling weight EPD means. Pelvic measurements were comparable between groups ( P > 0.10). Results of this study indicate that antagonistic selection for low BW and high growth rate is feasible using EPD. Therefore, the potential exists for increasing the genetic merit for growth with minimal birth problems associated with birth weight.