National Index Correlations and Actual vs. Expected Use of Foreign Sires
Differing selection indexes, genetic correlations < 1.0, and missing traits each cause reranking of the same bulls in different countries. To quantify, correlations were estimated using selection indexes from 15 major countries as of 2020. When different national indexes were used to compute rankings on the same EBV scale, most correlations were ≥ 0.80 and many were ≥ 0.90. Correlations were even higher when 1 index was applied to EBVs on all 15 scales. Thus, index definitions generally caused more reranking than EBV differences across scales. Foreign bulls were >80% of the top bulls in nearly all countries but often sired <50% of domestic cows. Reasons might include health restrictions, higher prices, lack of information, lack of technician service, or protectionism. Foreign bull use in each country is now documented in a web query. Because index correlations are high, many countries can improve genetic progress by using domestic bulls less and foreign bulls much more.
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