"Non-healing" claw horn lesions in dairy cows: Clinical, histopathological and molecular biological characterization of four cases.

The increasing prevalence of bovine digital dermatitis (BDD) contributes to a higher occurrence of secondary infections of exposed corium with spp. in bovine claws. "Non-healing" claw horn lesions (NHL) clinically resemble BDD lesions. They are severe, cause chronic lameness, and may persist for several months. They poorly respond to standard treatments of BDD and represent a serious welfare issue. In this study, four cases of NHL were classified clinically either as BDD-associated axial horn fissures (BDD-HFA; = 3) or BDD-associated sole ulcer (BDD-SU; = 1). In all four cases, pronounced multifocal keratinolysis of the stratum corneum, ulceration, and severe chronic lymphoplasmacytic perivascular to interstitial dermatitis were observed. All lesional samples tested positive for spp., (.) , and (.) by PCRs. BDD-HFA lesions contained as revealed by genetic identities of 93, 99, and 100%. Treponemes in the BDD-SU lesion were 94% homologous to phylotype PT3. Fluorescent hybridization (FISH) revealed extensive epidermal infiltration by treponemes that made up > 90% of the total bacterial population in all four lesions. FISH also tested positive for and negative for in all four cases, whilst only one BDD-HFA contained . Our data point to BDD-associated treponemes and constituting potential etiological agents in the development of "non-healing" claw horn lesions in cattle.