Conformation traits of Holstein cows and their association with a Canadian economic selection index

Pro$ is a Canadian economic selection index aimed to maximize profit by increasing production yields, while maintaining conformation and functional traits. Currently, there is an interest in understanding the individual contributions of conforma-tion traits recorded in Canada to the overall economic value of a cow and whether they are equally important. We used multiple polynomial regression and principal component analysis to assess the association of 26 conformation traits with Pro$ using relative breeding values (RBVs) from 9351 proven bulls. The best reduced regression model explained 72.5% of the variance in Pro$, with heel depth and body depth having the highest and lowest effect on Pro$ values, respectively. Four traits classified as intermediate optimum traits, e.g., teat length, showed significant linear association with Pro$ instead of quadratic, whereas bone quality was not significantly associated with the index. Principal component analysis indicated that highly profitable bulls share similar RBV, with a subclustering of bulls of daughters with better mammary system versus better dairy strength and feet and legs. These results provide understanding of the individual contributions of conformation traits to Pro$ and give information to guide the Canadian dairy industry on how to best consider these traits in recording and genetic evaluation programs.

Automated summary

This study assessed the association of 26 conformation traits with Pro$ using multiple polynomial regression and principal component analysis. The results showed that heel depth and body depth had the highest and lowest effect on Pro$ values, respectively, while traits like teat length showed a significant linear association with Pro$. The study provides important information for guiding the Canadian dairy industry on how to consider conformation traits in recording and genetic evaluation programs.