Genetic analysis of defective type characteristics and their genetic relationships with herd life of Canadian Holsteins

Heritabilities were estimated for 39 defective type characteristics of Canadian Holsteins. Approximately 100,000 records were available for analysis. Because these defects were scored into three categories (normal, minor, and serious), heritabilities were estimated using a threshold sire model with Gibbs sampling for numerical integration. Many of the traits had moderate (>0.20) heritabilities on the underlying scale, but heritabilities were much lower when transformed to the observed scale (none exceeding 0.09). Genetic evaluation was performed for each of the defects and genetic correlations of the defects with longevity were approximated by adjusting the product-moment correlations of ETA for the defects with ETA for herd life. The defective characteristics associated with the udder were the most strongly related to herd life. In general, the defective characteristics with the highest incidence rates also showed the greatest genetic relationships with herd life. Although some of the defective characteristics were moderately correlated with herd life, they generally have low incidence rates and are therefore not expected be of high economic importance themselves. Effects on herd life of the most important defects are already considered indirectly in the evaluation through their contributions to the type traits that are used to official ratings of sires for herd life. For these reasons a routine genetic evaluation of the defects seems unwarranted.