Bovine tuberculosis screening. Vet injecting a cow with tuberculin during an intradermal comparitive tuberculin test. This is the standard test used to screen cattle for bovine tuberculosis (TB). During the test tuberculin from Mycobacterium bovis is injected into the skin at one site in the neck. In most cattle infected with M. bovis the tuberculin causes localised sweeling. To ensure that any reaction is not caused by other mycobacteria, tuberculin from M. avium is injected at another site. The size and nature of the allergic reactions at each site are compared to determine a negative, positive, or inconclusive result.