Impact of Selection, Testing, and Operational Procedures on Genetic Progress in a Progeny Testing Artificial Insemination Stud

Abstract

Annual genetic gain for milk yield was simulated for an artificial insemination population of 115,000 dairy cows for different values of nine variables in young sire selection and sampling, and proven stud operation. Maximum genetic advance required the sampling of large numbers of young bulls annually. Increases in selection intensity of dams of bulls yielded uniform increases in rate of genetic change. Decreasing the number of bulls to sire young bulls to two to three each year and replacing one of these annually increased rates of genetic gain. Inbreeding effects were unimportant for these plans.An optimum progeny group size was 30 tested daughters per young bull sampled. Forty per cent of the tested cows should be bred to young bulls when 20% of the cow population is milk recorded. Advantages of low values for progeny group size and relatively high percentages of tested cows bred to young bulls decreased when higher percentages of cows were milk recorded. Rate of genetic gain in milk yield may be increased by utilizing each proven sire at the maximum rate and minimizing the loss of superior proven bulls. This allows maximum selection differentials among proven bulls.Selection for milk yield with some emphasis on other traits materially decreased rate of genetic gain in milk yield compared to selection for milk only. This effect was greatly reduced when high percentages of the cow population were milk recorded.North American artificial insemination breeding plans can be optimized by increasing the number of cows milk recorded, increasing the percentage of these cows bred to young bulls, and greatly increasing the number of young bulls progeny tested.