Effects on health and antioxidant status of oral supplementation of hazelnut skin extract in dairy calves with neonatal diarrhea: a randomized clinical trial in hospitalized patients.

Neonatal calf diarrhea (NCD) is a major contributor to morbidity and mortality in calves. Growing concern about antimicrobial resistance has spurred interest in phytotherapeutic alternatives, particularly polyphenol-rich extracts. Hazelnut skin (HS), a by-product of the confectionery sector, is a sustainable and underutilized source of polyphenols; however, its therapeutic efficacy in calves with NCD remains insufficiently investigated. This randomized, parallel-group clinical trial evaluated the effects of oral HS extract supplementation as an adjunct to standard medical therapy in hospitalized dairy calves with NCD. Sixty female Holstein calves were randomly allocated to a control group (CTRL; n = 30) or a treatment group (HS; n = 30) receiving 10 g/day of HS extract with milk for 5 days. All calves received standardized clinical management, including fluid therapy and antimicrobial administration. Clinical parameters, milk intake, body weight, hospitalization outcomes, sepsis scores, and blood oxidative stress biomarkers were monitored. No significant differences were detected between groups for clinical recovery, fecal score, hydration status, milk intake, weight gain, hospitalization duration, mortality, or oxidative stress markers. Clinical improvement over time was evident in both groups and was attributable to standard therapy. In conclusion, short-term oral supplementation with HS extract did not confer additional clinical or antioxidant benefits when added to conventional treatment in calves with NCD.