Relationships among Weights, Gains and Earliness of Maturing in Hereford and Angus Females

Abstract

The weight-age curves of 288 Hereford (H) and 296 Angus (A) females were used to obtain weights and gains at specific ages during the interval from 4 months to maturity. The effects of calving year, season of birth, sire and age of dam were used in a linear model to contrast the influence of genetic and environmental sources of variation on weights, gains and rate of maturing. Additive genetic variation (Va) was larger for immature H weights than A weights, but the A showed much larger Va values for monthly gains than the H. The mean estimates of h2 for body weight were not very different for the two breed groups but the A showed a larger range in h2 and had much smaller estimates of h2 at 4 and 36 months than the H. Large gains at young ages were associated with early maturing females while genotypes required for sustained growth rate into the advanced ages were associated with late maturing females.