Effect of freezing on the viability of Mycobacterium paratuberculosis in bovine feces.

Three bovine fecal specimens were cultured for Mycobacterium paratuberculosis before freezing and after frozen storage at -70 degrees C for 3 and 15 weeks. The losses in viability from 0 to 3 weeks of storage were significant (P = 0.01) for all three samples. The losses in viability between 3 and 15 weeks of storage were not significant (P greater than 0.05) for two specimens in which the M. paratuberculosis occurred naturally, but the loss was significant (P = 0.01) in a simulated specimen (M. paratuberculosis culture added to feces from a healthy cow).