Epidemiologic investigations of Mycobacterium avium subspecies paratuberculosis infections in Ohio dairy herds

The development of effective control programs for Mycobacterium avium subsp. paratuberculosis (MAP), the causative agent of Johne's disease, requires a complete understanding of the epidemiology of this agent in animal populations. The research described herein addresses several aspects of the epidemiology of this infection in dairy cattle.; Fecal culture and ELISA results collected from nine Ohio dairy herds involved in Johne's disease testing programs are described, and likelihood ratios for multiple levels of ELISA S/P ratios are calculated using these test records. The likelihood ratios calculated here suggest that the quantitative use of ELISA S/P ratios to predict the infection status of an individual cow from a MAP-infected dairy herd provides the most confidence when S/P ratios are considerably higher than the manufacturer's recommended cut-off value.; A prospective study of 55 Ohio dairy herds evaluated the relationships between farm management practices, milk production parameters and fecal cortisol levels. The influence of herd MAP-infection status on fecal cortisol levels was also assessed. Herd, management groups within herds and time of sample collection appear to significantly influence fecal cortisol levels; however, few specific management practices or milk production parameters that consistently influence these values were identified.; Production data for individual dairy cows were matched with results for MAP tests in order to compare testday production parameters between cows that were testpositive relative to those that were test-negative for both the ELISA and fecal culture. On a given testday, significant losses in milk production were identified for both fecal culture and ELISA-positive cows relative to test-negative cows. These observations provide additional information for dairy producers to consider as they make culling decisions regarding MAP test-positive cows.; Finally, a mail survey comparing the adoption of management practices recommended for Johne's disease control between Ohio dairy herds involved in testing programs relative to those herds that were not testing is described. Results of this survey demonstrate that, even if a producer believed his/her herd was not infected, participation in a testing program was associated with the adoption of management practices recommended for Johne's disease control.