Abstract

This study was designed to investigate the interaction between genotype and climate for milk and fat production traits of Iranian Holstein dairy herds. Milk and fat production data were grouped in 5 climates, on the basis of Extended De Martonne method. (Co)Variance components and genetic parameters of first lactation records from 514 herds were estimated by DFREML procedure. Estimation of genetic parameters by univariate animal model showed that heritability of milk and fat yields were from 0.22 to 0.30 and 0.06 to 0.26, respectively; that proved by the results of multivariate model. Genetic correlations between different climates ranged from 0.66 to 1 for milk yield and 0.16 to 1 for fat yield, respectively. Calculated genetic correlation between milk production traits in 5 various climates of Iran showed that there is a significant interaction between humid climate with other climates for both milk and fat yield traits. Using Spearman and Rank correlation for estimation of correlation between bulls breading values, for two traits showed the significant genotype by environment interaction between humid climate and Meditrranean climate for milk yield and between humid climate and other climates for fat yield.

Key words: Holstein, genetic correlation, breeding value, genotype by environment interaction.