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Submitted to: Journal of Dairy Science
Publication Type: Abstract Only Publication Acceptance Date: 3/23/2004 Publication Date: 7/25/2004 Citation: VanRaden, P.M. 2004. Genetic base and trait definition update [abstract]. Journal of Dairy Science. 87(Suppl. 1):412. Interpretive Summary: Technical Abstract: Base changes provide an opportunity to revise trait definitions and review genetic progress. Previous base changes in the United States were in 1965, 1974, 1984, 1989, 1995, and 2000. The next is scheduled for February 2005, with 18 of 25 countries in the Interbull yield evaluation planning to update their bases on this 5-year schedule recommended by Interbull. The others update every year or at each evaluation. Breeders today can view evaluations on many foreign scales using the Internet. Countries may define their own scales of expression and bases, but international marketing would be simpler with some uniformity and harmonization. In the Interbull udder health evaluation, 9 of 19 countries currently reverse their scales so that lower somatic cell scores (SCS) result in higher evaluations. Six countries in northern Europe report relative breeding values with means of 100, but different genetic SD multipliers (either 4, 5, 7, 10, or 12). The 4 countries that report clinical mastitis evaluations all reverse their scales. The United States could report predicted transmitting abilities (PTA) for udder health (UH) using the formula: PTA UH = -5 (PTA SCS - breed mean). This formula converts to the reversed, standardized PTA scale used by France and Spain with mean of 0 (instead of breed mean) and SD of 1. One unit of PTA UH would decrease somatic cell count by 13%. The range for PTA UH is similar to conformation, productive life, and daughter pregnancy rate PTA's. If many traits are evaluated, sub-indexes may provide the public with fewer numbers that are easier to remember and use. For most traits, genetic progress during the last 5 years was very similar to progress in the previous 5 years. The genetic variance base was last updated in 1995. The SD of PTA for yield traits will increase by about 10% as a result. At the last base change, net merit units were revised from per-lactation to lifetime profit. Selection indexes and genetic evaluations from breed associations, from USDA, and from other countries might be easier to use with further revision to obtain similar units, directions, and bases. |
