Successful implementation of a risk assessment and mitigation program to control bovine digital dermatitis at the herd-level.

This nonrandomized clinical intervention study was designed as a prospective, multicenter group comparison to evaluate the efficacy of a risk assessment and mitigation program to control bovine digital dermatitis (BDD). The program was implemented over a 1-year period on 9 intervention (INT) farms and 10 control (CTR) farms. Mainstays of the program derived from results of a previous BDD risk factor analysis. All farms were visited monthly to assess within-herd BDD prevalences to perform risk assessments and to treat BDD lesions with salicylic acid paste. Bulk milk samples were collected every 4 months. Diagnosis of BDD was based on visual inspection (clinical scoring) of the feet. Risk-associated management practices were identified on each farm, and management changes expected to prevent further introduction or spread of BDD within INT farms were suggested and agreed upon with farmers of the INT farms. Lesional biopsies were taken from a subset of cows of the INT group before and 2 months after treatment for histopathological and molecular biological examination to confirm histological and bacteriological cure in addition to clinical cure. The initial BDD prevalences for the INT and CTR farms averaged 39.8% (IQR 16.2) and 41.0% (IQR 12.4) for overall BDD lesions, 25.9% (IQR 10.8) and 26.2% (IQR 14.5) for active BDD lesions, and 22.1% (IQR 6.9) and 23.7% (IQR 22.3) for chronic BDD lesions, respectively. After 1 year of implementation, overall BDD prevalences were reduced to 14.1% (IQR 8.2) on INT farms but remained at 41.6% (IQR 10.8) on CTR farms. A significant decline in bulk milk anti-Treponema antibodies over the 1-year period was found in INT as compared to CTR farms. Considering the results of the histopathological examination, of 16S metagenomic sequencing and of the Fluorescence in situ hybridization as indicators for healing, 6/7 (85.7%) selected lesions were cured 2 months post completion of treatment. The results of this study show that the described BDD control measures can markedly reduce the within-herd prevalence of BDD. The proposed procedure might provide the basis for a nationwide BDD mitigation program that could be of importance also beyond national borders.