Associations of breeding values for disease traits and genetic markers in dairy cattle estimated with a mixed model.

Since 1985, all veterinary treatments on dairy cows in Sweden have been recorded and utilized for estimation of sire breeding values for resistance to clinical mastitis and to diseases other than clinical mastitis. The purpose of the present investigation was to study the relationship of blood groups and blood protein polymorphisms with these traits and to extend a method previously applied to international comparisons of dairy sires for milk production to estimation of marker gene effects. The data comprised 1171 AI sires of the Swedish Red and White dairy breed that had a blood typing record and breeding values for disease resistance. Information was available on the breeding values of sires, the number of daughters of each sire, and the relationships among sires. This information was used to deregress the sire breeding values to average daughter performances, which then were analyzed by a mixed linear model. The reduction in error variance that was due to inclusion of the markers in the model was small. Several substitution effects of the markers were statistically significant. The largest effects corresponded to a deviation of .7 percentage units for the frequency of veterinary treatments among the average daughters of the sires.