CONSISTENCY OF INTERNATIONAL GENETIC EVALUATIONS OF HOLSTEIN BULLS

Authors: POWELL, REX; WIGGANS, GEORGE; SIEBER, MARTIN - NAAB

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/1997
Publication Date: N/A
Citation: N/A

Interpretive Summary: One desirable characteristic of genetic evaluations is consistency. Except for base changes, expected changes between evaluations should be only those due to the addition of data if similar methodology is used. To examine stability of international evaluations, Aug. 1995 and Feb. 1996 evaluations from the International Bull Evaluation Service were examined for Holstein bulls from Canada, France, Germany, Italy, The Netherlands, and the U.S. Deviation of these evaluations from average genetic merit of bulls' parents was compared. Equations to convert evaluations between countries were calculated by bull birth year, and accuracy of converted national evaluations for predicting future international evaluations was determined. Average evaluations on a U.S. basis were unchanged for U.S. bulls; evaluations for bulls from France, Germany, Italy, and The Netherlands increased about 14 kg for milk and .4 kg for fat and protein. Average genetic merit of parents tended to overestimate bull merit, especially for U.S. bulls. French bulls that were full brothers to U.S. bulls had higher milk and protein evaluations on either country's basis. Intercepts for conversion equations to a U.S. basis increased by birth year and decreased for conversions from a U.S. basis. Future international evaluations generally were predicted more accurately by prior international evaluations than by more recent converted national evaluations. Continued use of the latest international evaluations by breeders is recommended. Refinements in methodology that increase consistency of international evaluations may be possible. However, users may need to accept some uncertainty and error in international evaluations because of limitations in currently available data and methodology.

Technical Abstract: International genetic evaluations in August 1995 and February 1996 for Holstein bulls from Canada, France, Germany, Italy, The Netherlands, and the U.S. were evaluated for consistency across time. Mean evaluations on a U.S. basis were unchanged for U.S. bulls; evaluations for bulls from France, Germany, Italy, and The Netherlands increased about 14 kg for milk and .4 kg for fat and protein. Mean genetic merit of U.S. parents of bulls sampled in Canada, France, Germany, The Netherlands, and the U.S. overestimated bull merit. Solutions for country of bull generally were not different for other countries relative to the U.S.; however, evaluations for German and Netherlands bulls were higher than evaluations for U.S. bulls with the same parent merit. French bulls that were full brothers to U.S. bulls had higher milk and protein evaluations on either country's basis. Intercepts for conversion equations to a U.S. basis increased by birth year and decreased for conversions from a U.S. basis. Future international evaluations generally were predicted more accurately by prior international evaluations than by more recent converted national evaluations; however, converted evaluations with substantial increases in data could be better predictors. Continued use of the latest international evaluations is recommended. Improvements in methodology that increase consistency of evaluations across time and location may be possible. However, users may need to accept some uncertainty and error in international evaluations because of limitations in available data and methodology.