Herd-level risk factors for infection with Mycobacterium paratuberculosis in US dairies and association between familiarity of the herd manager with the disease or prior diagnosis of the disease in that herd and use of preventive measures.

OBJECTIVE To evaluate associations among herd infection status, herd management practices, and familiarity of the herd manager with Mycobacterium paratuberculosis (Johne's disease) or prior disease diagnosis in that herd to support development of Johne's disease-control programs. DESIGN Population-based cross-sectional study. SAMPLE POPULATION 1,004 US dairies, each with > or = 30 cows, representing 79.4% of US dairy cows. PROCEDURE Questionnaires were administered to dairy managers, and blood samples were collected from cows during herd visits. Sera were tested for antibodies to M paratuberculosis, using a commercially available ELISA. Multivariable logistic regression analyses were used to evaluate associations between use of management practices, herd disease status, and familiarity of the manager with Johne's disease or prior diagnosis of Johne's disease in that herd. RESULTS Results from serologic testing revealed that 3.4% of cows and 21.6% of dairy herds were infected with M paratuberculosis. Factors associated with infection included number of cows in herd, region of country, percentage of cows born at other dairies, group housing for periparturient cows, and group housing for preweaned calves. Few preventive practices were positively associated with prior diagnosis of Johne's disease (time of separation of newborn calf from dam) or familiarity of the manager with the disease (teats and udder washed before colostrum collected). CONCLUSIONS AND CLINICAL RELEVANCE Risk factors associated with Johne's disease in this study confirmed those management practices generally recommended for disease control. An educational problem, however, is the finding that herd managers familiar with Johne's disease generally use management practices similar to those used by managers unfamiliar with the disease.