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Equity of elite cow status across states
R L Powell1, G R Wiggans, H D Norman
1Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350, USA.
Abstract:
Cows with superior genetic merit, based on an economic index for milk, fat, and yields (milk-fat-protein dollars), have been designated as elite by USDA. Because of the concern that adjustment for heterogeneous variance may have resulted in inequitable state representation for elite cows, the percentages of US cows with elite status were compared by state using evaluations of registered Holstein cows from 1990, 1991, and 1997. The numbers and percentages of eligible cows and the proportions of those cows that were designated as elite were determined by state from May 1997 evaluations of 772,302 registered and 1,499,729 grade Holstein cows; means and standard deviations for milk-fat-protein dollars were computed. Correlations were computed among the number of cows that were eligible for elite status, the number of cows that were designated as elite, the percentage of eligible cows that were designated as elite, and the mean and the standard deviation for milk-fat-protein dollars. Models were examined to for ability to predict the percentage of elite cows by state from mean and standard deviation for milk-fat-protein dollars. The number of elite cows for a state was highly correlated to the number of cows that were eligible for elite status. States with > 1.0% of eligible cows designated as elite had mean milk-fat-protein dollars that were higher than the US mean of $44, but standard deviations were equal to or slightly lower than the US standard deviation of $71. The mean value for milk-fat-protein dollars was associated with the state percentage of elite cows, but variation of the index was not related. However, the standard deviation for milk-fat-protein dollars was important in explaining the percentage of elite cows if the model also contained the mean value. Differences in the variation of lactation records across states or adjustments for those differences did not appear to cause inequity in designating elite status. Corresponding results for grade cows supported findings for registered cows.