Assessment of conformation scoring of the limbs as a potential explanatory factor for claw health in dairy cows

The selection of breeding animals is critical for a robust livestock population. Conformation trait scoring represents a practical approach to evaluate a cow's potential for productivity, longevity, and suitability for breeding. The scored traits are assigned to 4 subsections: frame and capacity, pelvis, limbs, and udder. Previous studies examining associations between specific limb conformation traits and the incidence of claw lesions have found low to moderate associations. This observational study (n = 21,145 cows) investigates associations between claw health and the score encompassing all traits of the "limbs" subsection and the final score per cow encompassing all subsections. This approach aims to capture potential associations between limb conformation and claw health that may not be linked to a single trait but the overall limb conformation. Claw health data were recorded by professional claw trimmers participating in the Swiss Claw Health Project. The claw health data were aggregated to 3 outcome values. For each recording, disorder occurrence and severity were combined to a value representing claw health in general encompassing all claw lesions. Also, 2 subvalues were created, one encompassing the stages of digital dermatitis only, the other one claw horn lesions only. The score for the "limbs" subsection showed significant associations with the occurrence of claw lesions in general and mechanical-metabolic lesions. The effect sizes, however, are small, ranging 10% to 59% increased odds across score categories for the occurrence of lesions of the digit in general and 10% to 104% for the occurrence of claw horn lesions. For cows with the lowest rating in the "limbs" trait subsection, the odds for higher lesion severity increases by 66%. To contextualize and compare these effect sizes, "parity" and "breed" were included based on previous studies. "Herd size" and "claw trimming frequency" were incorporated to represent management context. In higher parities, claw lesions in general and mechanical-metabolic lesions showed increased prevalences but prevalences of digital dermatitis decreased. Holstein-Friesian cows exhibited higher prevalences of most claw lesions compared with Brown Swiss, the difference being particularly pronounced for digital dermatitis. Larger herd size is associated with higher odds for claw disorders in general and digital dermatitis, and increased claw trimming frequency is associated with higher odds for digital dermatitis. The study concludes that limb conformation scoring can be a supportive tool in assessing a cow's potential for future claw health. To justify its use in breeding selection, further research on trait h² is needed. The small effect sizes reflect the multifactorial nature of claw health.