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Selection Instensity for Milk Production in Iowa Holstein Bull Dams¹

Department of Animal Science, Iowa State University, Ames 50010

ABSTRACT

The intensity with which young bulls are selected on the basis of their dams' estimated breeding value for milk production was investigated. Dairy Herd Improvement Association production records for seven years and information on the disposal of 1,113 male calves born in a single calving season were used. Of these calves, 106 died or were lost for other reasons, 713 were sold for beef, 254 were sold to other dairy herds, and 40 were kept for use in the herds where they were born. The dams of the last two groups averaged .35 standard deviation above the mean of all 1,113 dams in their estimated breeding value. This corresponds to saving the replacement bulls at random from the highest ranking 80% of all registered cows. Selection between rather than within herds primarily accounts for the low selection intensity.

¹ Journal Paper no. 1-6217 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project no. 1053.

² Present address: Heisdorf & Nelson Farms, Inc., 15305 N.E. 40th Street, Redmond, Washington 98052.