Bovine digital dermatitis in Victoria, Australia

Abstract

AIMS: The objectives of this study were to estimate the prevalence of digital dermatitis (DD) in Victoria, Australia, and to investigate which pathogens are consistent with typical DD lesions. Treponema-species are thought to be the primary causative agents of DD, but, it is considered that DD is a polymicrobial disease for which the causative pathogens are not fully understood. In Australia, limited published research on DD is available. The prevalence and causative pathogens of DD are not clear yet in Australia and this paper is one of the first to explore these subjects in this country. This information is important to aid in the development of education of producers and veterinarians, treatment methods and preventive measures for the disease. METHODS: Examination and sampling of limbs was undertaken at three knackeries in Victoria, Australia. After examination, limbs were classified as normal (N), active DD-lesion (A), dried or chronic DD-lesion (D) or suspected case of DD (S). A total of 823 cows were examined and accounts were taken from the their surrounding climate previous to their dead. Additionally, six skin biopsies were taken at each knackery, with a total of 18 biopsies: two biopsies from normal skin, two biopsies from active lesions and two biopsies from dried lesions. DNA extraction from the biopsies was performed and amplification of the V3 – V4 region of bacterial 16S rRNA was undertaken for diversity profiling. In addition, silver staining was done on eight of the skin biopsies. RESULTS: DD was detected in 29.8% of all cows. The prevalence of DD was significantly higher in dairy cows (32.2%) than in beef cows (10.8%). Of all cows with DD, 19.6% had active lesions, 84.9% had dried lesions and 66.9% had more than one foot affected. Analysis of the diversity profiling showed that the differential abundance of Treponema-species were significantly increased in active lesions, but decreased in dried lesions, compared with the normal skin biopsies. Actinobacteria, Proteobacteria, Firmicutes and Tenericutes were found to be significantly different in abundance in the DD lesions compared with normal skin biopsies. Silver staining of samples showed only mild inflammation and in two samples Spirochaetes were detected. CONCLUSIONS: The calculated prevalences show that DD is endemic in Victoria, Australia. Results of the 16S rRNA diversity profiling show that presence of Treponemaspecies was significantly different between the samples of DD lesions and normal skin. Considering the significant results in differential abundance for pathogens associated with DD lesions, when compared with the results from other studies, the findings of this study might suggest that the aetiology of DD in Australia is different from the aetiology of DD in other countries.