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United States Department of Agriculture

Agricultural Research Service

Title: Possible Global Scale for Ranking Dairy Bulls by Blending National Rankings

Authors
item Powell, Rex
item Vanraden, Paul

Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: July 24, 2001
Publication Date: N/A

Technical Abstract: International genetic evaluations are computed routinely for dairy bulls using multi-trait across country evaluation methods. Separate rankings are provided on the scales of member countries, but a global scale also could be useful in marketing across countries and for use by non-member countries. National units of expression were removed by dividing the evaluation on each scale by the country's standard deviation. These standardized evaluations were weighted by each country's fraction of global cow numbers and blended into a global evaluation. That approach is predicated on interest in breeding for a world market, but other weights may be considered. Fractions of global cow numbers were estimated by the proportions from each country of all daughters of evaluated bulls in the international evaluation. For the Holstein evaluation, countries with the largest cow numbers included the United States (18%), Germany (15%), France (13%), New Zealand (10%), and the Netherlands (9%). Twenty one other countries accounted for 35%. Conversion formulas for the global scale to and from each country scale may be needed. Correlations of bull evaluations on the separate country scales for protein averaged .976 within birth year. Correlations of the country scales with the global scale ranged from .955 to .995 with a mean of .988. Even with high correlations, there was reranking. Use of a global scale could ease the transition to an evaluation of data grouped and modeled by herd management and climate variables instead of national borders. Separate regional, country, or cluster rankings would still be needed to provide selection tools adapted to local conditions. Global evaluations would allow both participants and non-participants to select for a global market.

Last Modified: 10/1/2014
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