Use of Environmental Sampling as a Herd Screening Diagnostic Tool for the Detection of Mycobacterium avium Subsp paratuberculosis on Minnesota Dairy Farms

Johne's disease (JD) is a chronic and progressive intestinal disease in ruminants caused by Mycobacterium avium subspecies paratuberculosis (Map). The usual route of infection is fecal-oral. The disease manifests in adult cows and results in economic losses. Although Map does not propagate in the environment, it survives for long periods in different environmental conditions expected on many dairy farms. Johne's disease control programs have been developed in different countries and in several US states with a goal to test and classify herds of cattle as infected or presumptively noninfected with maximum accuracy and least cost. Generally, these programs utilize recognized laboratory tests such as ELISA or direct microbiological individual fecal culture. However, these tests have several disadvantages, especially when applied in herds with subclinical disease or low prevalence. Since Map is shed into the environment by dairy cattle through fecal contamination and appears to survive well, a better understanding of Map distribution in the environment could lead to improved herd-screening alternatives. Objectives of the study were: 1) to describe Map distribution and prevalence in the environment on Minnesota dairy farms, and 2) to assess the relationship between culture status of Map in the farm environment and fecal-pooled culture status on dairy farms.