Heritability of the Length of the Gestation Period in Dairy Cattle

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Abstract
Data consisting of 2063 gestations representing the 5 major breeds of dairy cattle in the University of Illinois herd were analyzed to determine the heritability and the variance of the length of the gestation period, so as to indicate the possibility of shortening the duration of pregnancy. The effect of sex of fetus and the variance components for service sire and sire of the dam were estimated. Heritability was estimated by multiplying the paternal half-sib correlation by 4 and by doubling the regression of offspring on dam. The paternal half-sib estimate of heritability refers to gestation as a characteristic of the fetus, whereas the regression estimate refers to gestation both as characteristic of the fetus and of the dam. The pooled estimates for the 5 breeds by the 2 different methods were 0.420 and 0.474, respectively. A comparison between the 2 heritability estimates, as well as a comparison of these estimates with repeatability estimates, demonstrated that the length of the gestation period was primarily a characteristic of the fetus. It was predicted that the mean length of the gestation period would be decreased by almost 10 days in 3 generations if 5% of the male and 50% of the female calves resulting from the shortest gestations were saved as breeding stock.