Genetic and Environmental Factors Affecting Weight of Beef Cows

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Abstract
Data from Angus, Brahman, Brangus, Hereford and Santa Gertrudis cows were obtained from 10 experiment station herds contributing to the S-10 Southern Regional Beef Cattle Breeding Project. Evaluated sources of variation in cow weight soon after parturition (PW) and at weaning (WW) included breed, sire, year of record, age in years, previous parity and calving month. Age generally accounted for a significant portion of the variation in cow weight. Differences in weight at succeeding ages were greatest between the younger ages and gradually decreased as age increased. The pattern of weight-change during the intervals from parturition to weaning and weaning to parturition appeared to vary with herd, age and breed. The effects of year and calving month varied widely across herds. Cows parous the previous year were lighter than nonparous cows for both PW and WW. Heritability and repeatability estimates for PW and WW were determined for each herd after the data were adjusted for accountable sources of environmental variation. Two-thirds of the 45 individual herd estimates of heritability exceeded 0.40. Repeatability estimates invariably exceeded 0.45. Copyright © 1967. American Society of Animal Science . Copyright 1967 by American Society of Animal Science