Evaluation of enzyme-linked immunosorbent assays performed on milk and serum samples for detection of paratuberculosis in lactating dairy cows

Objective-To determine whether results obtained for milk and serum samples with ELISAs intended for diagnosis of paratuberculosis in dairy cows were comparable to results obtained by means of mycobacterial culture of fecal samples. Design-Cross-sectional study. Animals-689 lactating dairy cows in 9 Ontario herds. Procedure-Milk, serum, and fecal samples were obtained from all cows. Fecal samples were submitted for mycobacterial culture. Serum samples were tested with a commercially available ELISA for antibodies against Mycobacterium paratuberculosis and preserved milk samples were tested with an indirect ELISA for antibodies against M paratuberculosis. Results-Results were positive for 130 of the 689 (18.9%) serum samples, 77 of the 689 (11.1 %) milk samples, and 72 of the 689 (10.4%) fecal samples. The level of agreement between results for milk and serum samples was only moderate. Proportions of positive results for serum and fecal samples were significantly different, but proportions of positive results for milk and fecal samples were not significantly different, In addition, results for milk samples had a higher level of agreement with results of mycoloacterial culture than did results for serum samples. Conclusions and Clinical Relevance-Results suggest that the indirect ELISA used on milk samples may be a convenient method of detecting paratuberculosis in dairy herds.