Heterogeneity of variance and dairy cattle breeding

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Abstract
The effects of heterogeneity among herds in phenotypic variance (σ2p) and in heritability (h2) on the accuracy of evaluation of dairy sires and cows are discussed with reference to estimates from field data. It is argued that heterogeneity of σ2P can be accounted for by using a (Bayesian) regression procedure. While the same procedure could be used to correct for heterogeneity of h2, in most practical situations the sampling errors of the h2 estimates for individual herds are likely to be so large that regressed estimates of h2 will differ little from each other, so constant values can be assumed.