Natural course of dermatophytosis-compatible lesions and clinical response to a single-dose Trichophyton verrucosum vaccine in intensively reared veal calves: a longitudinal field study

Bovine dermatophytosis is common in young cattle, especially in intensive veal-calf systems, yet large-scale longitudinal field data remain limited. Therefore, this study investigated the natural course of dermatophytosis-compatible lesions and the clinical response to a single-dose live attenuated Trichophyton verrucosum vaccine Trichoben®, (Bio 98 S.r.l., Italy) administered under field conditions in 709 intensively reared veal calves. The calves were enrolled at arrival (T0), randomly allocated at pen level to vaccination (Tr; n = 340) or control (Ct; n = 369) and dermatological inspections were performed every 15 days (T0 – T7). At arrival, 217/709 calves (30.6%) presented lesions compatible with dermatophytosis, and prevalence declined progressively to 18.5% at T1, 9.3% at T2, 2.3% at T3, and 0% by T6–T7 in both groups. Vaccination was not associated with time to new-onset lesions (HR 0.75, 95% CI 0.46–1.24; p = 0.263) nor with time to recovery (HR 0.83, 95% CI 0.61–1.12; p = 0.219), whereas farm of origin significantly influenced both outcomes. Lesions were predominantly located on head and neck throughout follow-up. No local or systemic adverse reactions were observed at 30 min or 48 h post-handling. Slaughter data were available for 133 calves; hot carcass weight did not differ between groups ( p > 0.05), and no association was detected between lesion occurrence or cumulative lesion count and carcass weight ( p > 0.05). The findings indicate that under these field conditions, dermatophytosis-compatible lesions showed rapid spontaneous regression in intensive veal-calf production systems characterized by short rearing cycles. A single-dose vaccination protocol was well tolerated but not associated with detectable clinical benefit. Further studies are needed to evaluate whether the two-dose vaccination protocol specified on the product label provides additional clinical and economic benefits in this rearing system.