SIRE X PASTURE PROGRAM INTERACTION EFFECTS ON PREWEANING PERFORMANCE OF CROSSBRED BEEF-CALVES

Records on crossbred calves from the eight crosses between Angus (A) and Hereford (H) cows, and A, H, Jersey, Simmental and Brahman sires, and raised in two pasture programs were used to assess sire x pasture interactions on preweaning traits. There were 518-734 calves from 252-318 dams and 122-166 sires in the data set; numbers vary by traits. Sires, AI or natural service, constituted a representative sample of the breeds. Pasture programs differed principally in the winter period (tall fescue hay vs. corn silage). Heritabilities across and within pastures were: 0.28 +/- 0.19 and 0.28 +/- 0.19 for birth weight (BW); 0.08 +/- 0.58 and 0.58 +/- 0.19 for weaning weight (WW); 0.30 +/- 0.41 and 0.71 +/- 0.19 for weight adjusted to 205 days (W205); 0.00 +/- 0.00 and 0.36 +/- 0.15 for daily pin (DG); 0.61 +/- 0.35 and 0.94 +/- 0.25 for frame score (FRAM); 0.14 +/- 0.38 and 0.53 +/- 0.22 for muscle score (MUSC); and 0.00 +/- 0.00 and 0. 14 +/- 0.21 for conformation score (CONF), respectively. Correlations between progenies of the same sire in different pasture programs are: 1.00 +/- 0.00 for BW; 0.13 +/- 0.99 for WW; 0.42 +/- 0.58 for W205; 0.00 +/- 0.00 for DG; 0.65 +/- 0.34 for FRAM; 0.27 +/- 0.71 for MUSC; and 0.00 +/- 0.00 for CONF. Except for birth weight, estimates (although imprecise) suggest that changes in the ranking of sires should be expected to occur between the two environments, possibly in part from incomplete adjustment for changes in season of calving between pasture environments for calves sired by the same sire.