Using the principle of the direct sire comparison method (BLUP), sire evaluations and variance components were calculated assuming herd x year x season and herdclass x year x season models for population with small herd size. Herd x year x season will be replaced by a classification containing herd level as an equivalent for single herds to reduce loss of records. From models with herd classes, one receives biased predictors since certain fixed effects between herds within a given are ignored. The bias of random effects is calculated by using the herd class x year x season model as a reduced herd x year x season model. Estimates for the additive genetic variance will be reduced, since adjustment for the genetic merit of different herds is made inaccessible when using herd class x year x season.

Rudolf Preisinger, J. Claus, E. Kalm

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XII. Biotechnology, selection experiments, parameter estimation, design of breeding systems, management of genetic resources., , 409–414, 1986
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