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Submitted to: Interbull Annual Meeting Proceedings
Publication Type: Proceedings Publication Acceptance Date: 6/2/2005 Publication Date: 8/1/2005 Citation: Van Raden, P.M. 2005. Inbreeding adjustments and effect on genetic trend estimates. International Bull Evaluation Service Bulletin 33:81-84. Interpretive Summary: Some national genetic evaluations of dairy cattle have included non-additive genetic effects, such as heterosis, but few have included inbreeding depression except in research studies. This study describes adjustments for inbreeding and for differing parity variances that were introduced as part of the February 2005 U.S. genetic evaluations. Inclusion in international evaluations require that any changes to the U.S. evaluations pass international bull evaluation service (Interbull) trend tests that measure the trend of 1st lactation animals, the current genetic trend, and the trend comparing current evaluations with the previous 4 years. Adjustments for inbreeding decreased genetic trend estimates noticeably but had small effects on Interbull trend tests. For Jerseys, the trend was reduced by 9% for yield traits and 32% for productive life and became nearly twice as negative for daughter pregnancy rate, yet none of the three Interbull tests identified the large biases from disregarding inbreeding. Parity variance adjustments caused only small decreases in genetic trend, but larger changes in trend tests. In trend test 1, Jersey protein decreased slightly by .006 genetic standard deviations per year when parity adjustments were applied, but if these adjustments were not applied, U.S. Jersey data for yield traits would have been discarded because Interbull trend test rules. Both adjustments show that trend tests are not good indicators of trend problems. Because inbreeding levels are now similar around the world and multi-trait across-country evaluations adjust for differences in genetic trend, researchers may want to test genetic trends, but national data should not be rejected from international evaluations based on those tests. Technical Abstract: Some national genetic evaluations of dairy cattle have included non-additive genetic effects, such as heterosis, but few have included inbreeding depression except in research studies. This study describes adjustments for inbreeding and for differing parity variances that were introduced as part of the February 2005 U.S. genetic evaluations. Inclusion in international evaluations require that any changes to the U.S. evaluations pass international bull evaluation service (Interbull) trend tests that measure the trend of 1st lactation animals, the current genetic trend, and the trend comparing current evaluations with the previous 4 years. Adjustments for inbreeding decreased genetic trend estimates noticeably but had small effects on Interbull trend tests. For Jerseys, the trend was reduced by 9% for yield traits and 32% for productive life and became nearly twice as negative for daughter pregnancy rate, yet none of the three Interbull tests identified the large biases from disregarding inbreeding. Parity variance adjustments caused only small decreases in genetic trend, but larger changes in trend tests. In trend test 1, Jersey protein decreased slightly by .006 genetic standard deviations per year when parity adjustments were applied, but if these adjustments were not applied, U.S. Jersey data for yield traits would have been discarded because Interbull trend test rules. Both adjustments show that trend tests are not good indicators of trend problems. Because inbreeding levels are now similar around the world and multi-trait across-country evaluations adjust for differences in genetic trend, researchers may want to test genetic trends, but national data should not be rejected from international evaluations based on those tests. |
