Deciphering the role of host-pathogen-microbiome interactions in the development of bovine digital dermatitis

Digital dermatitis (DD) is a painful, infectious, foot skin disease affecting ruminants worldwide. The disease is endemic on more than 90% of UK dairy farms and more than 50% of UK dairy cows are affected annually. In addition to pain and compromised animal welfare, DD is also associated with reduced milk yield, feed intake, and reproductive performance, and estimated to cost the UK dairy industry more than £74 million per year. Bacteria of the genus Treponema are considered the main pathogen associated with DD; however, the aetiopathogenesis and transmission patterns of the disease have not yet been elucidated. Current control strategies are generic and lack a substantial evidence base, relying on the empirical use of topical antibiotics and footbathing solutions containing heavy metals, such as copper sulphate, or formalin (carcinogen). We propose here to conduct a multidisciplinary, integrated study that will allow us to elucidate the role of host-pathogen-microbiome interactions in the development of DD, and advance our understanding of the disease's epidemiology, thereby offering tools to prevent the disease. More specifically we will:
1. Confirm existing and identify new genomic markers (SNPs) and genomic regions that are associated with resistance to DD and develop breeding values for this trait utilising a unique existing database.
2. Characterise the foot skin microbial communities (microbiome) before and during development of DD in a population of animals of known genetic propensity for resistance to DD and identify features of the microbiome associated with susceptibility to DD. We will deliver the first longitudinal, in depth characterisation of the foot skin microbiome in healthy animals and in animals with different DD infection patterns and of known genetic merit for resistance to DD. This will lead to a better understanding of the influence of the microbiome on host susceptibility to DD and has the potential to identify probiotic candidates; host genetic and management effects on the bovine foot skin microbiome will also be described.
3. Investigate the role of host-pathogen-microbiome interactions in the development of DD lesions and identify infection reservoirs. We will quantify pathogen burden and identify main infection reservoirs. We will also identify differences in pathogen burden, and skin integrity between animals of different genetic merit for resistance to DD and between animals with different DD infection patterns.
Mounting welfare and cost issues brought about by increasing prevalence of DD in bovine populations both nationally and worldwide demonstrate the timeliness of the proposed project.