Bacterial species associated with bovine digital dermatitis of Finnish dairy cows using 16S rRNA amplicon sequencing and Treponema species-specific 4-plex real-time PCR.

Bovine digital dermatitis (DD) is a widespread polybacterial skin disorder affecting dairy and beef cattle, leading to significant animal welfare and economic problems worldwide. The disease primarily affects the hind feet skin, causing painful inflammation between the heel bulbs and resulting in lameness. This study investigated the bacterial compositions in different DD lesion stages and in healthy skin biopsy samples from 151 dairy cows on 36 Finnish farms. The lesions were first classified into six categories, including healthy skin (M0) and samples from different DD lesion stages (M1-M4.1). Additionally, 13 healthy skin samples (M0HH) from cows in low DD (<5 %) prevalence herds served as controls. Bacterial profiling using 16S rRNA gene sequencing revealed the presence of three dominant phyla in active DD lesions: Firmicutes (39 %), Bacteroidota (31 %), and Spirochaetota (24 %), and altogether 11 Treponema species were detected. Real-time PCR was used to verify the presence of four common pathogenic considered species (T. phagedenis, T. denticola, T. medium and T. pedis), but only T. phagedenis, T. denticola were detected. This study indicated that DD is a polybacterial disease, with Treponema species abundant in active DD lesions. A higher Treponema count in Western Finland was associated with larger and more severe DD lesions, emphasizing the need for targeted and effective control measures in this region.