Skin Microbiota in Equine Pastern Dermatitis

Equine pastern dermatitis (EPD), a multifactorial syndrome, manifests as skin lesions of variable severity in the pastern area. Despite the widespread use of antibiotics for treating this condition, the role of bacteria in its pathology is still unclear. The objective was therefore to investigate how EPD itself and antibacterial treatment thereof lead to changes in the bacterial skin microbiota. A case-control study was therefore conducted with 80 client-owned horses that had at least one EPD-affected and one control pastern each. Horses were grouped by the form of EPD, the severity grade and their type of pretreatment. Skin swabs were obtained, and the bacterial diversity was compared between the groups. Bacterial alpha diversity was reduced in affected pasterns (P < 0.001) and this reduction was significantly associated with EPD lesions (P < 0.001), but not with the type of pretreatment (P > 0.14). Analyses of beta-diversity confirmed a disordering of the skin microbiota (P = 0.004), that was particularly profound in more severe lesions. The type of pretreatment was not primarily decisive for these perturbations but was likely an enhancing factor. Four differentially abundant families were detected, of which Staphylococcaceae were the most distinct. Their relative abundance was significantly increased in affected pasterns (P = 0.011), particularly in those that had previously received antibacterial treatment. Altogether, our study demonstrates that changes in the microbiota are associated with the form and severity of EPD. A primary and/or secondary role of bacteria as well as the propriety of antibacterial treatment should therefore be further investigated.