R. L. Powell and H. D. Norman
Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350
International evaluations for Holstein bulls were calculated by the International Bull Evaluation Service with data available in February 1995 from Canada, Denmark, France, Germany, Italy, Sweden, The Netherlands, and the US using current methodology with either correlations between countries of unity (0.995) or estimates of less than unity. To determine which of the two evaluation methods was most accurate, results of the two sets of evaluations for milk, fat, and protein yields for each country were compared with national evaluations in 1999. The 1999 national evaluations were assumed to be the best estimates of true genetic merit on a particular national scale. To reduce the impact of the part-whole relationship that results from earlier national data, a key part of the study was restricted to bulls with data from at least twice as many daughters for 1999 national evaluation as for 1995. Correlations and standard deviations of differences from later national evaluations showed no advantage to accounting for genetic correlations between countries. For bulls without national data in the earlier international evaluations and, therefore, no data in common with the later national evaluation, the advantage from using variable genetic correlations for yield was small. Thus, the use of variable genetic correlations had marginal value.
(Key words: genetic correlation, international evaluation, genetic evaluation)
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2000 J. Dairy Sci. 83:1552
© 2000, by the American Dairy Science Association. All rights reserved.