Comparison of Holstein bull semen sources on milk traits in Isfahan province in Iran

Abstract. This research provides a comparison of productivity of daughters in Iran sired by bulls from Canada, Europe, Iran, and the United States. Data were collected by the Animal Breeding Center of Iran on pedigree and first lactation performances of 10,192 Holsteins sired by 186 imported (including: 39 European, 73 American, 74 Canadian) and 133 Iranian bulls, which had their first calving in 35 dairy herds in Isfahan province. The results showed that American and European daughters had the highest performances for milk yield. The highest mean for fat yield was related to European daughters. American sires on average had the highest genetic potential for yield traits; however, they had the lowest fat percentage among compared sire groups. Canadian sire group was intermediate relative to American, European and Iranian groups. Higher intercepts and regression coefficients of conversion equations for American sires showed that more returns will be achieved from one genetic point superiority of American sires relative to Canadian sires in the environments of Isfahan province. The Iranian sire group had the lowest predicted transmitting ability means for both milk and fat yields and a negative predicted transmitting ability mean for fat percentage. This study showed that due to low to intermediate predicted transmitting ability correlations between foreign evaluations and the evaluations made by this study, direct selection based on foreign national evaluations would not lead to optimal results for the traits concerned. So, the genetic potential/expression of imported genetic materials needs to be reevaluated by the Animal Breeding Centers of Iran.