Cow-level prevalence of paratuberculosis in culled dairy cows in Atlantic Canada and Maine.

The prevalence of Mycobacterium avium ssp. paratuberculosis (Mptb) in culled dairy cattle in Eastern Canada and Maine was determined to be 16.1% (95% confidence interval 13.8 to 18.3%) based on a systematic random sample of abattoir cattle. Mesenteric lymph nodes and ileum from 984 cows were examined by histologic and bacteriologic methods. Histological testing was far less sensitive than bacteriologic methods for detecting infected cattle. A seasonal pattern of positive cows was also detected, with the highest proportion of cows being Mptb-positive in June (42.5%). Overall, body condition score was not associated with prevalence of Mptb isolation.