Genetic characteristics of the coronet scores related to Holstein cattle hoof health in Japan.

Hoof disorders are crucial factors leading to dairy cattle culling. These disorders are difficult to detect, diagnose, and record, causing animal health problems and serious economic losses. The coronet score is a new hoof health indicator developed by the Dairy Herd Improvement Program of Japan. This score is assigned on a 5-point scale and can easily be determined by examining the degree of redness and swelling around the hooves. To determine whether coronet scores can be used to genetically improve hoof health, we investigated non-genetic factors in the score, developed a genetic analysis model, and estimated genetic parameters. Coronet scores were collected from 1280 herds in 28 prefectures once a month from 2014 to 2021. Furthermore, 1,598,878 test-day records of 94,951 cows from the first- to third-parity and pedigree information of 216,416 individuals were used in the analysis. Results revealed that herd size, parity, age, test month, and lactation stage influenced the coronet score. Additionally, the heritability of the coronet score estimated via the herd-test-day model was 0.027, and genetic trends deteriorated in sires and cows. Overall, we demonstrated that coronet score is a heritable trait, suggesting that hoof health could be genetically improved by selection for coronet score.