Heritability of Fertility in Dairy Cattle

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Abstract
An analysis of data on approx. 1000 cows sired artificially by Holstein bulls in New York state has permitted a study of the relative reproductive efficiency of groups of artificially sired paternal half-sibs located on different farms. The analytical procedure consisted of estimating the components of variance due to sires, herds, year-season, cows, and certain interactions. Based on the estimates of the components of variance, repeatability of fertility measured by non-returns to 1st service in a population of half-sisters within the same herd is estimated to be 0.027, and repeatability of this measure in a population of cows by different sires within the same herd is estimated to be 0.051. The avg. intraherd repeatability is estimated to be some value between 0.027 and 0.051. The heritability of non-returns to 1st service is estimated to be 0.004. When calving interval is used as the measure of fertility, heritability is estimated to be zero. These low values of repeatability and heritability indicate that under the existing conditions selection for high fertility is ineffective when non-returns to 1st service or calving interval are used as a measure of reproductive efficiency.

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