Retrospective analysis of the accuracy of conversion equations and multiple-trait, across-country evaluations of Holstein bulls used internationally.

In 1995, the multiple-trait across country genetic evaluation procedure replaced regression-based conversion equations as the preferred method for international genetic comparisons of dairy bulls. In the present study, February 1999 estimated breeding values of 632 foreign Holstein bulls that were used in Canada, Germany, Italy, The Netherlands, Sweden, and the US were compared with January 1995 predictions from home country data only. January 1995 predicted breeding values for each importing country were calculated using three methods: the multiple-trait, across-country evaluation procedure; conversion equations based on the multiple-trait, across-country evaluations; and conversion equations based on the Wilmink method. Mean correlations between 1999 estimated breeding values in the importing countries and 1995 predictions from international data were from 0.76 to 0.81 for all methods. The multiple-trait, across-country evaluation procedure is expected to lead to selection of different bulls, because bulls were allowed to be ranked differently in each country, but no significant increase in accuracy of selection was observed. The lack of improvement in accuracy of prediction was most likely due to limitations in data structure. International genetic comparisons are largely driven by data from a relatively small number of evaluated bulls with exported semen. Data from siblings and more distant relatives provide only weak, indirect genetic links between countries, and inclusion of such data seems to provide a minimal improvement in accuracy. Limitations in data structure might be alleviated by methods that define environments by climate or management factors rather than country borders.