Relationship between negative skin test with Johnin after vaccination and post mortem findings.

One hundred and seventy-six cattle, vaccinated against paratuberculosis in the first month of life with a whole-cell inactivated vaccine, containing Mycobacterium paratuberculosis suspended in a water/oil emulsion, were tested with intradermal Johnin between the ages of five and 14 months. Negative results in the skin test occurred more frequently in animals found positive in post mortem examinations (P = 0.008) using histological, microscopical and cultural techniques.