Effect of environmental factors and fetal and maternal genotype on gestation length and birth weight of Holstein calves.

Records of gestation length and birth weight on 1522 live single births (from 1958 to 1976) of Holstein calves were from 81 sires and 552 dams. Average gestation length was 282.3 days, and average birth weight was 42.9 kg. Male calves were carried 1.7 days longer than female calves and weighed 2.9 kg more at birth. Both gestation length and birth weight increased with parity. Calves born in spring and summer were carried shorter times and weighed less than those born in fall and winter. Heritabilities of gestation length and birth weight as progeny traits were .73 and .51 and as maternal traits were .19 and .26. Genetic correlations between gestation length and birth weight were .46 as a progeny trait and .35 as a maternal trait. Genetic correlations between progeny traits and maternal traits were negative. The phenotypic correlation between gestation length and birth weight was .37, and environmental correlation was .30.