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Detection of Heterogeneous Variance in Herd Production Groups

Department of Animal Science, University of California, Davis 95616

ABSTRACT

The detection of heterogeneous variance across herd groups is based largely on data stratified by mean herd production. Such stratification is analogous to selection on herd means. This introduces the possibility of biased estimates of genetic and residual variances. Results presented show that Henderson's Method 3 estimates of the residual variance are unbiased by selection on herd means. However, reductions in sums of squares for sires have different expected values in no selection and selection models. The magnitude of this bias is evaluated with a small-scale simulation. Extension of these results to other methods of variance estimation reveals a potential bias from selection on herd means.