Impact of second-country data of foreign bulls on international evaluations of dairy bulls.

Second-country data of foreign bulls are a primary source of information for international genetic comparison of dairy sires. Potential problems exist with this data, because imported semen is expensive, and progeny may receive preferential treatment. The extent of potential bias in international sire evaluations from inclusion of second-country data of imported bulls was examined using data from 25,205 Holstein bulls evaluated in the US, Canada, Italy, Holland, and Germany. Mean changes in international evaluations of potential candidates for export from inclusion of second-country data were < 50 kg EBV for milk and < 3 kg EBV for fat and protein, and changes in the international evaluations of imported bulls were < 100 kg EBV for milk and < 3 kg EBV for fat and protein. These changes suggest that bias from preferential treatment of progeny of foreign sires was not a significant problem for the countries examined. Application of reduced weight to second-country data of foreign sires can further reduce the chance of bias from preferential treatment. Based on this study, inclusion of second-country data of foreign bulls in international sire evaluations is appropriate, and problems due to preferential treatment are few.