Selection for weaning weight and postweaning gain in Hereford cattle. II. Response to selection

Irgang, R.; Dillard, E.U.; Tess, M.W.; Robison, O.W.

Journal of Animal Science 60(5): 1142-1155

1985


ISSN/ISBN: 0021-8812
PMID: 4008362
Accession: 001457019

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Abstract
Single-trait selection was practised in 3 lines of Hereford cattle. Bulls were selected within sire families for increased body weight at weaning in the WW line, for postweaning gain in the PG line, and at random in the control line. 2467 calves produced from 1967 to 1981 were considered. Environmental effects were estimated from the controls (method 1) and from multiple regression procedures (method 2). Phenotypic and environmental time trends were negative for body weight at weaning, and generally were positive for postweaning gain. Estimated genetic gains for body weight at weaning in the WW line were 1.07+or-0.51 kg per yr in bulls and 0.62+or-0.36 kg per yr in heifers using method 1, and 0.50+or-0.31 in bulls and 0.10+or-0.17 in heifers using method 2. Corresponding values for postweaning growth in the PG line were 0.85+or-0.40 and 1.03+or-0.24 kg per yr in bulls and 0.30+or-0.28 and 0.37+or-0.12 kg in heifers. Correlated genetic gains for body weight at weaning in the PG line were larger than direct gains, whereas genetic gains for postweaning gain in the WW line were smaller than direct gains. Using the 1st method, estimates of realised hsuperscript 2 for body weight at weaning were 0.31+or-0.18 in bulls and 0.22+or-0.13 in heifers. For postweaning gain, hsuperscript 2 was 0.31+or-0.13 in bulls and 0.06+or-0.12 in heifers. Using the 2nd method, hsuperscript 2 for body weight at weaning was 0.09+or-0.08 in bulls and 0.02+or-0.07 in heifers. Corresponding values for postweaning gain were 0.29+or-0.10 and 0.11+or-0.08. Joint estimates of the realised genetic correlation between body weight at weaning and postweaning gain were 0.69+or-0.18 and 0.46+or-0.31 for methods 1 and 2 resp. Variation in selection response was evaluated using quasi-replicates. Results of this study indicate that selection for postweaning gain improved both body weight at weaning and postweaning gain faster than selection for body weight at weaning. [For Pts. 1 and 3 see pp. 1133-1141 and 1156-1164 of the same number of the Journal of Animal Science].