HETEROGENEITY OF VARIANCES ACROSS REGIONS OF NORTHERN GERMANY AND ADJUSTMENT IN GENETIC EVALUATION

Based on a total of 2,305,000 records for protein yield in days 1-100 of first lactation and in the entire first lactation variance componen ts were estimated within 36 subregions from northwestern Germany using REML with an animal model. For days 1-100, heritability estimates ran ged from 0.27 to 0.40, and estimates for phenotypic variances ranged f rom 73.8 kg(2) to 122.6 kg(2). Pattern of results for the entire first lactation was very similar. Phenotypic variances as well as heritabil ities were concluded to be heterogeneous across subregions. To account for heterogeneous heritabilities in an evaluation assuming a common h eritability records were standardized. Adjustment factors were derived by first calculating the optimum fractions to be selected from each s ubregion and then calculating the corresponding adjusted phenotypic va riances so that the differences in heritabilities between the subregio ns were reflected in the phenotypic variances. Using this method and c omparing it to an evaluation with unadjusted records more cows were se lected from subregions with higher heritabilities, thus showing that t his method may be useful to reduce potential bias: from heterogeneous heritabilities. (C) 1998 Elsevier Science B.V.