The application of multiple-trait random regression model to estimation of genetic parameters and genotype by environment interaction in Iranian Holstein dairy cattle

The existence of genotype by environment interaction on milk production traits of Iranian Holstein dairy cattle was investigated by considering recorded performance of daughters of sires at different calving seasons regards as different traits. In the current study، recorded data on Holstein cows between 2001 and 2010 were used. For production traits (milk yield، fat percentage and protein percentage)، genotype by environment interaction were estimated by using multiple-trait random regression sire model. Additive genetic and permanent environmental variances of milk production traits did not vary at different calving seasons. Heritabilities for 305-d production in spring، summer، autumn and winter calving seasons were 0. 26، 0. 29، 0. 27 and 0. 24 for milk yield، respectively; 0. 28، 0. 30، 0. 30 and 0. 28 for fat percentage، respectively and 0. 42، 0. 45، 0. 40 and 0. 38 for protein percentage، respectively. The genetic correlations for 305-d milk production traits between different calving seasons were higher than 0. 93 and that no significant genotype by environment interaction was indicated. The Spearman rank correlations between estimated breeding values of 20 top sires between summer and autumn and also between summer and winter were 0. 68 for protein percentage and the re-ranking of sires between these seasons were observed. In conclusion، results from this study indicated that there were interactions between genotype and season of calving for milk production traits in Iranian Holsteins dairy cows. The results of current study can be used to increase the accuracy of sire selection.