Genotype x environment interaction in the Greek Holstein population

Genetic improvement of dairy cattle in the Greek dairy industry is based mainly on the use of imported semen of progeny tested bulls or direct importation of 7 month pregnant heifers. As there are major differences from the exporting countries in the production system, i.e. herd management and feeding system, the study of the magnitude of genotype x environment interactions (GxE) on milk yield is of significant importance. The data set for this study was provided by the Holstein Association of Greece covering a time period from 1999 to 2008 and comprised of 11459 completed lactations from 45 dairy farms. The sires under study originated from 12 countries. Breeding values for the bulls under study were estimated in Greece using an animal model. The fixed factors included were herd, herd production group, year – season of calving and number of lactation. Repeated milk records of 7079 cows having completed at least the first three consecutive lactations were used in the analysis. The heritability of 305 days milk production was 0.23. The determination of any possible GxE interaction was based on the ranking correlation of the bulls breeding values, as estimated from the responsible organizations in each of the sire’s origin with the corresponding breeding values estimated from the Greek dairy population. The correlation coefficients were between -0.32 and 0.45 depending on the bull’s country of origin. All of them were non significant. A comparison of the mean values of the production traits in Greece and the bulls’ countries of origin indicates the factors that could explain the lack of significant correlations.