ACCURACY OF FOREIGN DAIRY BULL EVALUATIONS IN PREDICTING US EVALUATIONS FOR YIELD

Authors: POWELL, REX; SANDERS, ASHLEY; NORMAN, H

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/16/2004
Publication Date: 7/25/2004
Citation: Powell, R.L., Sanders, A.H., Norman, H.D. 2004. Accuracy of foreign dairy bull evaluations in predicting United States evaluations for yield. Journal of Dairy Science. 87(8):2621-2626.

Interpretive Summary: The accuracy of genetic estimates of merit for yield and somatic cell score based on foreign daughters as predictors of U.S. performance was investigated by comparing Interbull evaluations that did not include U.S. daughters with the August 2003 U.S. domestic evaluation based only on U.S. daughters for 286 bulls. Average differences were near zero, although at the time of importation, the evaluations tended to be overestimates for yield. Correlations for evaluations of yield and somatic cell score were near the expected correlations. Interbull evaluations based solely on foreign daughters are generally good predictors of the U.S evaluations for yield.

Technical Abstract: Combining foreign daughter data with domestic information in dairy bull genetic evaluations has been shown to improve prediction of future domestic evaluations for U.S. bulls. This study focused on foreign bulls by evaluating the accuracy of Interbull evaluations (foreign daughters) in predicting the latest domestic evaluations (U.S. daughters). The most recent February or August Interbull evaluations without U.S. daughters were matched with current (August 2003) USDA evaluations based only on U.S. daughters. A minimum reliability of at least 80% for yield and 70% for SCS was required in both evaluations. This provided pairs of evaluations based on different daughters (foreign or U.S.) for 286 bulls (60 bulls for SCS). Mean Interbull reliabilities on the U.S. scale were 88% for yield and 84% for SCS and the mean U.S. reliability for the current evaluations were 91% for yield and 80% for SCS. Correlations between the Interbull and domestic evaluations were 0.90, 0.87, 0.90, and 0.87 for milk, fat, protein, and SCS respectively. Expected correlations were 0.89 for yield and 0.82 for SCS. Mean differences between the Interbull and current domestic evaluations were near zero. These foreign bulls had graduated from progeny test programs (selected for positive Mendelian sampling) before being marketed in the United States. Thus, parent average was a substantial underestimate of merit. The small average differences between evaluations from foreign and US daughters and high correlations indicate that Interbull evaluations based solely on foreign daughters are useful predictors of the U.S. evaluations for yield and SCS, providing better estimates than the alternative, parent averages.