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Title: POSSIBLE GLOBAL SCALE FOR RANKING DAIRY BULLS BY COMBINING INTERNATIONAL EVALUATIONS EXPRESSED ON NATIONAL SCALES

Author
item Powell, Rex
item Vanraden, Paul

Submitted to: Interbull Annual Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/30/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: The need for procedures to express genetic evaluations of dairy bulls across national borders has long been recognized, and the current international procedure of expressing trait evaluations on more than two dozen national scales makes the selection of breeding stock and the presentation of marketing materials difficult. Genetic evaluations for Holstein bulls on a global scale were calculated by weighting May 2001 Interbull (International Bull Evaluation Service, Uppsala, Sweden) evaluations expressed on 27 national scales. Interbull evaluations on national scales were weighted by the country's proportion of total daughters from all bulls (population size). Weighting of Interbull evaluations on national scales was fairly robust; alternatives of equal weighting or weighting by inverse of population size produced practically the same group of top bulls as weighting by population size. Thus, the method for combining Interbull evaluations expressed on national scales had only minor impact and was much less important than use of all data. "Borderless" rankings that make use of all available data can be used by breeders in countries that do not participate in Interbull and by international marketers to purchase and to sell germplasm without referring to a particular national scale.

Technical Abstract: Genetic evaluations for Holstein bulls on a global scale were calculated by weighting May 2001 Interbull (International Bull Evaluation Service) evaluations expressed on 27 national scales. Interbull evaluations on national scales were weighted by the country's proportion of total daughters from all bulls (population size). Correlations within birth year between Interbull evaluations on national scales and evaluations on a global scale ranged from 0.961 to 0.998 (mean of 0.988). Number of top 100 bulls for protein yield that were in common between national and global scales ranged from 54 to 94 and was related significantly to mean genetic correlation used in the Interbull analysis between a country and all other countries. Weighting of Interbull evaluations on national scales was fairly robust; alternatives of equal weighting or weighting by inverse of population size produced practically the same group of top bulls as weighting by population size. Correlations among the three global scales within birth year were 0.999. Thus, the method for combining Interbull evaluations expressed on national scales had only minor impact and was much less important than use of all data.