Genetic correlations between type traits of young Polish Holstein-Friesian bulls and their daughters

The objective of this study was to evaluate the usefulness of young bulls' conformation scores in a national type evaluation system. For this purpose the genetic correlations between conformation traits of sires and the same type traits of their daughters were estimated. Young bulls were evaluated as required for registration in the herd book and for entering progeny testing. Data were 7 linearly scored (1-9 scale) and 3 descriptive (scored from 50 to 100) conformation traits of 933 young bulls born between 2005 and 2008, and the same traits evaluated in their 65 479 daughters. A two-trait animal model was used to estimate genetic correlations between the type traits of bulls and their daughters. (Co) variance components were estimated by a Bayesian method via Gibbs sampling. Two linear models were used: the linear model for bulls included fixed linear regressions on age at evaluation, fixed effects of herd and classifier, and random additive genetic effect; the linear model for cows contained fixed effects of herd-year-season-classifier, lactation stage, fixed linear regression on age at calving, and random additive genetic effect. Estimates of bulls' heritabilities for all analyzed traits ranged from 0.07 for feet and legs to 0.25 for body depth. Heritabilities of cows were the lowest for rear legs rear view (0.05) and foot angle (0.06), and the highest for size (0.43). The genetic correlations between similarly described traits of bulls and their daughters were moderate to high (0.42-0.91). The lowest genetic correlation (0.42) was for chest width, and the highest (0.91) for rump angle. The magnitude of genetic correlations between pairs of type traits of sires and daughters was high enough to suggest that the body conformation of dairy cows can be improved by making use of some measurements taken from young bulls. Including highly correlated bull scores for size, rump angle, and three linear leg traits in the evaluation system could improve the accuracy of type breeding value evaluation.