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Estimation of Genetic Change in the Registered Holstein Cattle Population¹

Department of Animal Science, Iowa State University, Ames 50011

L. P. Johnson

Holstein Association, Brattleboro, VT 05301

ABSTRACT

We examined pedigrees of 440,702 males and 526,956 females born during 1960 through 1979 and registered in the herdbook of the Holstein Association. Annual trends in genetic merit of sires, dams, maternal grandsires, and maternal granddams were determined from their estimated transmitting abilities. Genetic merit of parents changed substantially after more accurate procedures for estimating transmitting abilities were introduced in 1968. Rates of change for genetic merit of sires were larger than corresponding changes in dams. Annual genetic change for the male and female populations was estimated by two methods. The sum of annual changes in the average estimated transmitting abilities of sires and dams yielded estimates of annual genetic change. In addition, estimates of annual genetic change were obtained by doubling trends in the animals' average estimated transmitting abilities. Both methods yielded similar results in the female population. For 1971 to 1979, annual genetic change for females was approximately +55 kg milk, +1.5 kg milk fat, and –.007 milk fat percentage. In the male population, estimates differed between methods. Smaller estimates of annual genetic change resulted from doubling the rate of change in the bulls' average Predicted Differences. This method should yield more accurate estimates of genetic change when bulls with genetic evaluations are representative of the population. Estimates of annual genetic change for 1971 to 1979 from the latter method were 84 kg milk, 2.6 kg milk fat, and –.006 milk fat percentage.

¹ Journal Paper No. J-11694 of the Iowa Agriculture and Home Economics Experiment Station, Ames. Project No. 1053.

² Department of Dairy Science, Virginia Polytechnic Institute and State University, Blacksburg 24061.

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