Association of Hoof Disorders with Inflammatory, Oxidative, Metabolic, and Milk Quality Biomarkers in Holstein–Friesian Dairy Cows

Hoof disorders are a major cause of reduced productivity and compromised welfare in dairy cows and are frequently accompanied by systemic inflammatory and metabolic disturbances. However, the relationships among different types of hoof lesions, oxidative stress, inflammation, metabolic status, and milk quality remain incompletely understood. Therefore, this study evaluated inflammatory, oxidative stress, metabolic, and milk quality biomarkers in Holstein–Friesian dairy cows with different hoof disorders and assessed their ability to discriminate lame from healthy animals. A total of 451 cows were classified as healthy (n = 210) or affected by horn (n = 190), infectious (n = 32), or degenerative (n = 13) hoof lesions; six cows with combinations of lesions that precluded unambiguous assignment to a single category were excluded from lesion-category comparisons. Blood and milk samples were analyzed for inflammatory cytokines, acute-phase proteins, oxidative stress markers, metabolic indicators, and milk quality traits. Compared with healthy cows, animals with hoof disorders, particularly those with infectious lesions, exhibited significantly higher concentrations of haptoglobin, serum amyloid A, IL-1β, IL-6, TNF-α, malondialdehyde, β-hydroxybutyrate, non-esterified fatty acids, cortisol, somatic cell count, and somatic cell score, whereas antioxidant biomarkers (total antioxidant capacity, glutathione peroxidase, superoxide dismutase, and catalase), IL-10, milk yield, fat content, and protein content were significantly lower (all p < 0.001). Correlation and principal component analyses revealed close associations among inflammatory, oxidative stress, metabolic, and milk quality variables. Receiver operating characteristic analysis identified IL-6 (AUC = 0.947), TNF-α (AUC = 0.934), haptoglobin (AUC = 0.921), and serum amyloid A (AUC = 0.913) as the biomarkers with the highest discriminatory performance for distinguishing clinically lame cows from healthy animals. Multivariate logistic regression identified β-hydroxybutyrate (OR = 3.24), malondialdehyde (OR = 2.26), somatic cell count (OR = 1.41), IL-6 (OR = 1.12), and TNF-α (OR = 1.09) as variables independently associated with lameness after evaluation of potential biological covariates. Overall, hoof disorders were associated with pronounced inflammatory, oxidative, and metabolic alterations accompanied by impaired milk quality. These findings suggest that IL-6, haptoglobin, serum amyloid A, and β-hydroxybutyrate may represent promising biomarkers for assessing and monitoring clinically established lameness in dairy cows. Further longitudinal studies are warranted to validate these findings and to evaluate the potential clinical utility of these biomarkers for lameness monitoring.