Longitudinal study of the distribution of Mycobacterium avium subsp. paratuberculosis in the environment of dairy herds in the Michigan Johne's disease control demonstration herd project.

The objective of this study was to describe the distribution of Mycobacterium avium subsp. paratuberculosis (MAP) in the environment of infected dairy farms over time. Johne's disease (JD) prevalence was monitored annually in 7 Michigan dairy herds. Environmental samples were collected bi-annually and cultured for MAP. Of 731 environmental samples that were cultured, 81 (11%) were positive. The lactating cow floor and manure storage areas were the areas most commonly contaminated, representing 30% and 33% of positive samples, respectively. When herd prevalence was > 2%, MAP was cultured from the lactating cow floor and/or manure storage area 75% of the time. When herd prevalence was < or = 2%, MAP was never cultured from samples collected. For every 1 unit increase in number of positive environmental samples, within herd JD prevalence increased 1.62%. Environmental contamination with MAP is consistent over time on infected dairy farms, and management practices to reduce environmental contamination are warranted.