Bulk tank milk ELISA for detection of antibodies to Mycobacterium avium subsp. paratuberculosis: Correlation between repeated tests and within-herd antibody-prevalence

The repeated BTM-recordings were highly correlated with a correlation of 0.80 between samples collected 1.5 months apart. The within-herd antibody prevalence significantly influenced this estimate (p < 0.0001), which dropped to 0.60 when corrected for the within-herd antibody prevalence. Although the test-results were relatively consistent and correlated with the within-herd prevalence, the magnitude of the test-values makes it difficult to use the BTM-ELISA for surveillance of MAP infections in practice.