Date of this Version
Heritability estimated by year of freshening for first-lactation milk records of artificially sired Holstein cows in the northeastern United States from daughter on dam regression averaged about .34 on the linear scale and .31 on the logarithmic scale. Little change could be detected from 1965 to 1982. Number of daughter-dam pairs was 197,338. Heritability estimates on the .5 and .4 power scales always were bounded by estimates on the linear and log scales. Heritability estimates were smallest in low management levels. Residual standard deviations for measurements to the .4 power were similar for all levels of management for a particular year, although a tendency was for the residual standard deviation to be larger in the low management level and smaller in the high management level.