Epidemiologic survey of hoof health in grazing cattle under tropical condition and etiology of bovine digital dermatitis

Hoof lesions and the resulting lameness are considered one of the three most common occurrences in dairy cattle and despite the advancement of knowledge his prevalence is increasing over the years. The objective of this study was to determine the prevalence of foot lesions and lameness in grazing herds in Minas Gerais state and identify the main risk factors. Furthermore, this work aims to investigate the core pathogens related with digital dermatitis in grazing cattle under tropical conditions. A total of 48 farms divided equally in four production groups were visited, 2267 animals were mobility scored and 392 animals had all hoofs inspected. A questionnaire and a checklist were applied to the owner or stockholder to identify risk factors. The prevalence of hoof lesions, lameness and severe lameness were calculated and a multivariable linear regression model were built to identify risk factors. Digital dermatitis lesions were sampled for further analysis by histopathology, fluorescent in situ hybridization (FISH) and gene sequencing. Among the evaluated cows, 16.0% were scored as lame and 6.8% as severely lame. Nearly all cows presented at least one type of hoof lesion, of which heel horn erosion (HHE; 90.1%), white line fissure (WLF; 50.4%), and digital dermatitis (DD; 32.7%) were the most frequent. DD was present in all but two farms. Sole ulcer was observed in only one animal. HHE and DD presented the highest proportion of severe cases, while the majority of WLF were mild. DD was correlated to an increase chance of 2.5 times in mobility score. Track features was the most significant factor increasing more than threefold the odds for HHE, WLF and sole hemorrhage (SH). Several factors related to unhygienic conditions such as frequency of corral cleaning, condition of corral exit, access to pile of manure and keep animals in paddocks during the dry period were identify as risk factors for hoof lesions. Poor human-animal relation was related with an increase odds for SH while patience of the farmer handling the cows on the track decrease in more than half the odds for interdigital hyperplasia. The microbiological analyses of DD samples revealed Treponema spp. as the most abundant bacteria and eleven different Treponema strains belonging to the six major phylotypes were identified. Furthermore, D. nodosus was also identified in a high proportion of samples in both FISH and sequencing. It was present in areas with mild epithelial damage and together with Treponema. Collectively, our results demonstrate that digital dermatitis is the main concern and the biggest cause of lameness in grazing cattle under tropical condition and it is related with unhygienic environment. The present data support the hypothesis that Treponema constitutes the main pathogens in DD and it further suggests D. nodosus as another potentially important pathogen.