مقايسه عملكرد توليدي نتاج گاوهاي نر هلشتاين داخلي و خارجي در شرايط مختلف اقليمي ايران

Comparison of Progenyʹs Production Performance from Internal and External Holstein Bulls in Different Climatic Conditions of Iran

To investigate progenyʹs production performance of Iranian and foreign Holstein bulls in different Iranian climatic conditions, 9673 first lactation records of milk and fat yield in 13 Herds from 1985 to 2005 were used. Based on Extended Demarton Method herds were grouped into 4 climates including of Dry cold, Ultra-Dry cold, Humid Temperate, and Sub-Dry cold. Cowʹs performances in different climates were considered as separate traits. Using a multivariate animal model, (co)variance components and genetic parameters were estimated. Heritability of milk and fat yield ranged from 17 to 33 percent and from 9 to 14 percent, respectively. Genetic correlations for milk and fat yield in different mentioned climates varied from 0.55 to 0.98 and from 0.22 to 0.94, respectively. Genetic correlations for both traits between Humid Temperate and other climates were lower than 0.80, indicating the presence of genotype and environment interaction between them. Genetic correlations between Dry-Cold and Ultra-Dry cold for both traits were more than 0.90, indicating that we could consider performances of dairy cows in these two climates as one trait. Comparison of daughterʹs estimated breeding values (EBVs) of sires from different sources showed that the lowest (except in Sub-Dry cold) and the highest daughters EBVs for both traits were belonged to Iranian and New Zealand bulls, respectively.