J. Anim Sci.
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J. Anim Sci. 1981. 52:257-264.
© 1981 American Society of Animal Science
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Monte Carlo Study of Genetic Evaluations Using Sequentially Selected Records

E. J. Pollak1 and R. L. Quaas

University of California, Davis 95616 and and Cornell University, Itbaca, New York 14853

Abstract

The effect of selection for weaning weight on the subsequent evaluations of animals for postweaning gain and yearling weight was examined with simulated beef cattle records. One hundred herds were generated. Each herd contained 10 sires and 200 calves to be evaluated. The evaluations of interest were those obtained from the use of weaning weight records for all calves in a multiple-trait evaluation of gain and yearling weight and those obtained with records from selected animals only. Comparisons were made in terms of bias observed in the predictors. Evaluations based on records from selected animals only were consistently biased for both sires and calves. The magnitude of the bias was influenced by the intensity of selection at weaning (the more intense, the larger the bias) and by the correlation between the traits of interest and weaning weight (larger bias observed in yearling weight evaluations). The trend was to overestimate breeding values for poor animals and to underestimate values for superior animals. Incorporating records for all animals for the trait under direct selection (weaning weight) eliminated the bias in the evaluations for subsequently measured traits.

Footnotes

1 Present address: Dept. of Anim. Sci., Cornell Univ. Ithaca, NY 14853.




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