Factors affecting birth weight of Santa Gertrudis calves

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Abstract
SUMMARY Birth weights of 568 Santa Gertrudis calves by 15 sires out of 111 different dams over a 14-year period were obtained from a herd in Cuba. Year of birth, season of birth, sex of calf, sire and dam all had highly significant influences upon birth weight but there was no effect of dam age or parity. Calf inbreeding ranged from 0 to 25% and led to a decrease of 012 kg in weight for each 1% increase in inbreeding. Calves surviving to weaning or dying between birth and weaning were of similar mean weight. Calves dying at birth were some 4·53 kg above the overall average of 38·59 kg. Sire effects covered a range of some 9·85 kg in birth weight. Heritability of birth weight estimated from an intra-class correlation between paternal half-sib groups was 0·67. Repeatability estimates were of the order of 0·22 from intra-class correlation and 0-24 on the basis of regression of later on earlier records. The overall least squares mean weight of 38-59 kg was several kg higher than previous estimates in the literature.