A biometrical study of weight of Angus and Hereford cows and growth of their progeny

Abstract

Data were obtained from the Alabama, Georgia and Texas Agricultural Experiment Stations in conjunction with the Southern Regional Beef Cattle Breeding Project, S-10. Records from more than 1600 Angus and Hereford calves and their dams were analyzed to evaluate weight-age relationships independent of major genetic and environmental sources of variation. Also, weights of 746 heifers taken at birth, weaning and beginning and ending the postweaning test and first calving weight of 213 cows were analyzed to determine genetic and phenotypic relationships among weights of females. Data from Angus and Hereford cattle were generally analyzed separately. Constants were fitted for genetic and environmental sources of variation in all statistical analyses of weight or weight change of dam and growth of their progeny. Weights of heifers were adjusted for environmental effects by least-squares constants and partial regression coefficients. Estimates of genetic and phenotypic statistics were then calculated from paternal half-sib analyses of variance and covariance on adjusted data. The partial cubic regression of post-partum weight on age of cow was evaluated independent of effects of herd, sire, calving season, first calving age, previous parity and fecundity. Age accounted for a large part of the variation in cow weight. Cows attained their mature weight at 6 to 7 years. Angus cows reached maturity slightly earlier than did Herefords, which averaged 25-30 kg. heavier than Angus cows. Cows that had raised all of their calves before reaching 7 years of age were about 30 kg. lighter at that age than cows that had not raised all of their calves to weaning during the same period. ...