The ability of a test to accurately distinguish an animal's Johne's status will depend on the test, the lab conducting the test and the stage of infection. Which tests are best to use and in which combination will be unique to your herd's situation. You should thoroughly discuss your options and the ramifications with your herd veterinarian. The Tests Nine tests are currently used to detect Johne's Disease. Four detect the bacterium that causes Johne's Disease, three detect serum antibodies, and two detect cell-mediated immunity.
Most experts agree fecal culture has been the most accurate diagnostic test to use on live animals.
It holds an advantage over serological tests for seedstock producers wanting to limit the chance of false positives. They do, however, require experienced technologists to conduct the tests and are moderately expensive. It takes up to 16 weeks to get results. That means an animal that's shedding M. paratuberculosis could continue to contaminate its environment and infect other animals during the four months it takes to get results back. Also realize some animals may be intermittent shedders - they may shed the organism for a period, then stop, only to start shedding again.