Effect of Some Genetic and Maternal Environmental Variations on Birth Weight and Gestation Length in Holstein Cattle

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Abstract
Records on 536 gestations from 258 Holstein cows representing 6 different sire lines were studied by standard partial regression and analysis of variance. Birth weight and gestation length were analyzed for possible effects of sire line, in-breeding and sex of calf, and weight, inbreeding, parity, and uterine horn pregnant in the dam. The average in breeding of inbred dams was 24.7% and of inbred calves, 24.9%. Inbreeding of the dam had insignificant effects both on birth weight and on gestation length. The standard partial regression of birth weight on inbreeding of calf was negative and statistically significant. Inbreeding of the calf, however, had no significant effect on gestation length. Both birth weight and gestation length increased with the parity order of the dam, but the effect was significant only in the case of birth weight. Weight of dam had a positive effect (P<0.05) on both dependent variables. There were significant differences between sire lines both in birth weight and in gestation length. Male calves averaged 5.92 lb. heavier at birth and were gestated 1.44 days longer than females. The right uterine horn produced heavier calves (average 1.78 lb.; P< 0.05) than the left horn, but the side pregnant had no significant effect on gestation length. Interactions between the effects of sire line, sex of calf, and uterine horn pregnant were also tested and none was significant.