Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/1997
Publication Date: N/A
Citation: N/A Interpretive Summary:
Technical Abstract: National genetic evaluations for yield have accounted for heterogeneous variance among herds since 1991. Cows with superior estimated genetic merit based on an economic index of milk, fat, and protein PTA (MFP$) have been designated elite by USDA. Because proportions of elite Holstein cows from various States changed considerably since 1991, breeders wanted verification that adjustment for heterogeneous variance, which has a regional component, was fair for herds and cows in all areas of the US. For 795,158 Holstein cows eligible for elite status based on July 1996 USDA-DHIA evaluations, mean and standard deviation (SD) of MFP$ and number and percentage elite were examined by State. Percentage of eligible cows designated elite ranged from .10 to 1.96% for 45 States with at least 1000 eligible cows and from .67 to 1.75% for 16 States with at least 10,000 eligible cows. States with more eligible cows had more elite cows but not a higher percentage elite. Number of eligible cows was significantly correlated with number of elite cows (.98 for 45 States and .97 for 16 States) but was nonsignificantly correlated with percentage elite (-.31 and .05). Correlation between percentage elite and mean MFP$ was highly significant (.65 for 45 States and .71 for 16 States); correlation between percentage elite and standard deviation of MFP$ was nonsignificant (.25 and -.28). States with higher mean MFP$ had higher percentages elite, but SD of MFP$ by State was not a significant factor. However, SD of MFP$ combined with mean MFP$ was significant in explaining percentage elite. Although State differences for SD alone were not associated with proportions of elite cows, SD differences did aid the prediction of percentage elite when mean MFP$ also was considered.