Influence of postweaning gain interval on estimates of heritability and genetic correlations.

Heritability and phenotypic environmental and genetic correlations of postweaning gains for intervals of 28 to 224 d were calculated from data on 2,410 crossbred steers and 3,088 Hereford bulls. Gains were essentially linear for the 224-d interval. As the length of the performance interval increased from 28 to 224 d, heritability of gain increased from .12 to .55 among the crossbred steers and from .09 to .24 among the Hereford bulls. There was no tendency for heritability to be larger or smaller for intervals of like duration initiated early or late in the 224-d interval. Heritability of individual animal regressions of weight on days was evaluated as an alternative measure of gain/d. Heritabilities were not different between daily gain and regressions when measured over the same intervals. Genetic correlations were generally positive and much larger than the environmental or phenotypic correlations, indicating that genetic influences tended to persist from one interval to another. Genetic correlations between intervals tended to become smaller as the number of days separating the intervals increased.