STABILITY OF INTERNATIONAL DAIRY BULL EVALUATIONS

Authors: Powell, Rex; Wiggans, George; SIEBER, MARTIN - NAAB

Submitted to: Interbull Annual Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 6/23/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: One desirable objective of genetic evaluation is consistency (or stability) over time. If similar methodology is used, expected changes between evaluations should be only those due to the addition of data; mean evaluations for groups of bulls in subsequent evaluations should be stable. To examine the stability of international evaluations, August 1995 and February 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 the average genetic merit of bulls' parents also was compared by country, and equations to convert evaluations between countries were calculated by birth year of bull. 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. Evaluations for top bulls generally declined. Relative standing of U.S. bulls overall and among top bulls declined. 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. To provide breeders worldwide with more accurate evaluations, refinements in methodology that would increase consistency of international evaluations across time and location may be possible. However, users may need to accept that a degree of uncertainty and error must be accepted in international evaluations because of current methodology.

Technical Abstract: August 1995 and February 1996 international evaluations for Holstein bulls from Canada, France, Germany, Italy, The Netherlands, and the U.S. were examined to determine stability of evaluations 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. Evaluations for top bulls generally declined. Relative standing of U.S. bulls overall and among top bulls declined. Deviation of evaluations from parent average (PA) was analyzed. Mean PA of U.S. parents of bulls sampled in Canada, France, Germany, The Netherlands, and the U.S. overestimated bull merit; differences were largest for U.S. bulls. Solutions for country of bull generally were not different for other countries relative to the U.S. On a U.S. basis, both German and Netherlands bulls were higher than U.S. bulls from a model that accounted for PA; however, these differences were less than 1 kg of PTA protein. French bulls that were full brothers to U.S. bulls had higher milk and protein evaluations on either country's basis. Conversion equations were computed to determine if they differed by bull birth year. Intercepts for conversion equations to a U.S. basis increased by birth year and decreased for conversions from a U.S. basis. Both intercepts and regression coefficients increased by birth year for equations from The Netherlands to France but showed no trend in the other direction. Improvements in methodology that would increase consistency of evaluations across time and location may be possible. Alternatively, users may need to accept that a degree of uncertainty and error must be accepted in international evaluations because of current methodology.