Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 2004
Publication Date: July 1, 2004
Citation: Wiggans, G.R., Gengler, N., Wright, J.R. 2004. Type trait (co)variance components for five dairy breeds. Journal of Dairy Science.87(7):2324-2330.
Interpretive Summary: The multi-trait genetic evaluation of type traits improves accuracy of evaluation of each trait using information from correlated traits. Variances and covariances were estimated from recent data to improve accuracy of these correlations. The largest change from previous estimates of heritability was 0.11. The new estimates also support the recent implementation of heterogeneous variance adjustments. These changes will improve the accuracy of type evaluations and improve their contribution to indexes of overall genetic merit.
(Co)Variance components were estimated for final score and 14 or 15 linear type traits for the Ayrshire, Brown Swiss, Guernsey, Jersey, and Milking Shorthorn breeds. Appraisals from 1995 or later were used. New estimates were calculated to accommodate changes in scoring of traits and because of the change from multiplicative to additive adjustments for age and stage of lactation. The method of adjustment was changed to better support the within iteration adjustment for heterogeneous variance implemented in 2002. Largest changes in heritability were an increase of .10 for rump angle for Milking Shorthorn and a decrease of .11 for udder depth for Jersey. These new estimates of (co)variance components should provide improved accuracy of type evaluations, particularly for traits that have changed in variance over time.