Effect of glucocorticoids on cows suspected of subclinical infection withM. paratuberculosis

Glucocorticoids were administered to 10 heifers suspected of subclinical infection with Mycobacterium paratuberculosis. Three animals remained untreated. M. paratuberculosis was isolated from the internal organs of 2 animals after this treatment but not from any of the control group. Delayed type hypersensitivity and lymphocyte reactivity towards Johnin and purified protein derivates of M. avium and M. bovis were depressed. A sharp increase in total leucocyte count, due to an increase in neutrophil numbers, occurred. In the three untreated animals these parameters did not change during the experiment. A decrease of specific immunological reactivity towards M. paratuberculosis occurred, but not to such an extent that clinical disease developed.