Genotype-environment interaction in milk production under Danish and Bulgarian-Czechoslovakian conditions

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Abstract
SUMMARY First lactation records from 971 daughters of 93 Red Danish Milk-breed bulls exported as pregnant heifers from Denmark to 4 Bulgarian and 21 Czechoslovakian herds were analysed and compared to results from corresponding half-sib groups under Danish field progeny tests. Average butterfat production in East European tests was 75% of that in Danish tests. The results indicate that the true genetic variance and the heritabilities for milk yield, fat content and butterfat yield are higher under the Danish conditions than under the corresponding East European conditions. The genetic correlations between the two environments are estimated to be 0·91, 0·97 and 0·79 for milk yield, fat content and butterfat yield, respectively. Because of insufficient correction for environmental effects, these estimates are considered to be lower than the true parameters. It is concluded that selection of proven sires in the Danish main population for use in the small East European subpopulations will result in a higher genetic improvement rate than will sire testing and selection within the subpopulations.