Digital dermatitis (DD), a polybacterial skin infection of the bovine foot, is among the most common causes of lameness on Canadian dairy farms. The current prevention and treatment methods require constant attention and resources, with regular footbathing and topical treatment necessary to keep outbreaks under control. While a vaccine is desired by many in the dairy industry, the complete etiology of DD is not fully understood, making vaccine development currently unattainable. With the more recent recognition of painless preclinical lesions that develop before the painful clinical stages, an opportunity has presented itself to further study the bacteria present in preclinical lesions among dairy cows in different herds. The microbiota of preclinical lesion tissue is previously unstudied in a commercial dairy housing cows without any sign of clinical DD. In addition, while DD risk factors and herd prevalence have been studied in Ontario, Alberta, and internationally, no published research has indicated whether Saskatchewan dairy farmers perceive and manage DD in a similar manner.
The first objective of this research was to describe the known DD risk factors identified on six selected Saskatchewan dairies that are endemic for clinical DD and one dairy non-endemic for clinical DD. The surveys used to obtain these results also served to ensure that study herds were representative of other Canadian herds, and to recruit and further describe the participant dairies for part two of this project. The second objective was to describe the presence, abundance, and identity of DD-associated bacteria in heel skin tissue, fecal, and slurry samples from cows on these seven dairies.
A survey was used to recruit participant dairies in Saskatchewan who then completed an on-farm questionnaire at the time of sample collection. Samples were collected from cows with varying stages of DD and were subjected to 16S rRNA gene amplicon sequencing.
The survey data indicated that respondents were representative of other Saskatchewan dairies in terms of production and housing, and representative of Canadian dairies regarding record keeping, trimming practices, and perceived importance of hoof lesions causing lameness. The dairy non-endemic for clinical DD practiced more stringent biosecurity than the other participant dairies. The most critical findings of this study are that preclinical lesions were present on the dairy that was free of clinical DD, that these did not progress to clinical disease, and the near complete lack of the bacteria associated with the transition of preclinical lesions to the clinical stages on the dairy non-endemic for clinical DD. Continued stringent biosecurity appears necessary to keep clinical DD-associated treponemes from proliferating in these tissues that are otherwise susceptible to clinical DD
