Genetic Relationships Between Coronet Score and Type Traits Related to Hoof and Body Size in Holstein Cattle in Japan.

Hoof disorders in dairy cows reduce productivity and increase culling risk, causing economic losses and animal welfare concerns. The coronet score is a 5-point indicator of hoof health (1 = healthy; 5 = severe) that may be useful in breeding programs. However, genetic relationships between coronet score and type traits remain unclear. We estimated genetic correlations between coronet score and type traits related to hoof and body size in Holstein dairy cows. Data from 24,174 first-lactation Holstein cows were analyzed. Coronet scores were obtained from test-day records, whereas type traits were evaluated once during first parity. Genetic correlations were estimated using two-trait animal models with Gibbs sampling. The genetic correlation between coronet score and feet and legs was -0.71, indicating that cows with higher feet and legs scores tended to have lower coronet scores. Positive genetic correlations ranging from 0.28 to 0.40 were observed between coronet score and body size traits, suggesting that larger cows tended to have higher coronet scores. These results indicate that coronet score is favorably associated with current breeding goals aimed at improving lifetime performance and controlling excessive body size. The coronet score may be a useful selection indicator for improving hoof health.