Persistence of Mycobacterium avium subsp. paratuberculosis (Map) in field dried hay fertilized with bovine slurry from Map infected herds.

Objective: Use of Map contaminated slurry or manure to fertilize crop fields is generally considered a risk factor for the Map transmission, although data on survival of Map in crops are sparse. Therefore, the persistence of Map on crops fertilized during the autumn-winter period with slurry or manure coming from Map infected herds was studied. Methods: Ten Map infected herds with different prevalence levels of infection were selected. Culture and PCR tests were performed on environmental samples collected from the infected farms to assess the level of Map contamination. The same tests were performed on crop samples collected at three different time-points: (1) on fresh hay before harvesting; (2) on hay after field drying; (3) on dried hay at the beginning of its use for animal feeding. Results: The environmental samples had massive presence of Map in the manure and slurry used to fertilize the fields. The tests performed on the fresh hay samples, collected before harvesting, showed a single positive result by PCR (10%) and were always negative by culture. The hay samples collected after field drying and at the beginning of their use for animal feeding were always negative in both culture and PCR. Conclusion: These results suggested that under the described conditions, the contamination risk for field dried hay, although possible, is of limited importance for the spreading of infection. On the other hand this must not be underestimated in uninfected herds purchasing forage.