The study of genotype by environment interaction for milk production traits in ‎Iranian Holstein cattle

The aim of this study was to investigate the effect of genotype by environment interaction through calculating the rank correlation between estimated breeding values of bulls in Iran and in Interbull. The data of 2,000,378 records of 305 days of milk, fat and protein production in the first, second and third lactations in years of 2004 to 2021 were used. The records were from daughters of 9603 sires in 3,444 herds. In model one, the breeding values of animals in the multivariate analysis for milk, fat and protein production of first lactation were estimated. In model two, a repeatability model was used to estimate breeding values in the multivariate analysis for milk, fat and protein production from first to third parity. Rank correlation were estimated between Iran and Interbull for bulls which had at least 20 daughters in 10 herds. In the single-parity model, the rank correlations between the estimated breeding values in Iran and Interbull for milk, fat and protein were 0.76, 0.75 and 0.76, respectively. In the multiple-parity model, the rank correlations between the estimated breeding values in Iran and Interbull for milk, fat and protein production were 0.48, 0.43 and 0.51, respectively, which shows the interaction of genotype by environment. The results showed different rank correlations for two types of models used. Therefore, due to genotype by environment interaction, the rank of bulls in Iran could be different from Interbull estimates.