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Measurement of Genetic Trend

Department of Animal Husbandry, Cornell University, Ithaca, New York

ABSTRACT

A method for estimating trend in genetic merit is described for a population consisting of animals sired by artificial insemination and of animals sired naturally. The contemporary comparison of unselected progeny of an artificially used sire and their naturally sired contemporaries making first records under the same conditions constitutes a unit of observation. This observation consists of an effect of the artificially used sire, an effect due to the random sample of natural service sires with progeny making records in the same year-season, and a random error. This model is fitted by the method of least squares to estimate trend in natural service progeny. Trends in merit of artificially sired daughters and of naturally sired daughters were estimated by this procedure for New York DHIA Holstein herds. From 1951 to 1959 the natural service genetic merit increased by 17 lb. of fat and 399 lb. of milk, whereas the genetic merit of the artificially sired population increased by 25 lb. of fat and 512 lb. of milk. The artificially sired daughters were superior in all seasons for milk and fat yield.