Dam's infection progress and within-herd prevalence as predictors of Mycobacterium avium subsp. paratuberculosis ELISA response in Danish Holstein cattle.

Understanding the primary routes of transmission of Mycobacterium avium subsp. paratuberculosis (MAP) is pivotal to manage the pathogen in cattle herds. MAP is transmitted both vertically and horizontally, and both the dam's stage of infection and the prevalence in the population are therefore potentially important for MAP transmission control. The objective of this study was therefore to assess the dam's infection progress and the within-herd test-prevalence as predictors of MAP infection in Danish dairy cattle. MAP specific antibody ELISA records from 95,025 dam-offspring pairs were combined with test-prevalence estimates from 939 Danish Holstein herds. The odds of testing ELISA-positive given the within-herd test-prevalence and the time-period a dam had had MAP specific antibodies were estimated for the offspring. Both dams and offspring were tested as adults, and parity-group was used to correct for the effect of age. The results showed that both the within-herd test-prevalence and the dam's infection progress were significant predictors, while the dams that had tested positive when giving birth and up to 0.7 years after were more likely to have offspring that would test positive. The odds of testing positive were about 1.5 to 2.5 times higher for these offspring, compared to offspring of dams that never tested positive. Furthermore, offspring born in high (>5% ELISA-positive) and medium (2.5 to 5% ELISA-positive) prevalence herds had 9 and 3, respectively, times higher odds of testing positive, compared to animals born in a low prevalence herd. The variance heterogeneity reduced 81% through the included predictors. The results of this study suggest that irrespective of the prevalence, offspring of dams with MAP specific antibodies should be considered as high-risk animals when managing the infection in cattle herds, but both the prevalence and the dam's infection status are important in MAP control.