Which Johne''s Test? Four options to choose from

February 2, 2009 06:00 PM

If you are hauling skinny cows to the livestock auction with any frequency, think Johne's disease, a contagious, slow-progressing disease caused by Mycobacterium paratuberculosis.

This silent killer usually infects an animal when it is extremely young but does not show itself until the animal is an adult. In the meantime, the infected animal is shedding the bacterium and infecting herdmates as well as newborn and young calves.

A national study has found that approximately 22% of U.S. dairy farms have at least 10% of the herd infected with Johne's. The study determined that herds with a high Johne's disease clinical cull rate experience an average loss of $227 per cow. Herds with a low cull rate have an average loss of $40 per cow. This loss is due to reduced milk production, early culling and poor conditioning at culling.

"Research has brought many, many good Johne's tests to the table,” says Mike Collins, a veterinarian specializing in Johne's at the University of Wisconsin–Madison. "Which test to use is best answered by research conducted by the ‘Best Test Team.'” This team consisted of researchers from Colorado State University, Texas A&M University, University of California–Davis, University of Minnesota and University of Wisconsin.

Test options include bacterial culture, gene detection assays, antibody assays and histopathologic evaluation of tissue. The team of researchers found that bacterial culture of six fecal samples obtained from the environment is the most cost-effective method for determining whether a dairy herd is infected.

"However, finding that all six samples yield negative results does not guarantee the herd is not infected,” Collins states. "The second-best testing option is PCR assay of fecal samples collected from the environment.

"Owners of herds with negative culture or PCR test results on all six samples should enroll their herds in the U.S. Test-Negative Program.”

A test gaining popularity is the milk ELISA. This test is less costly than a standard serum ELISA and sample collection can be incorporated into routine DHIA sampling.

"Testing recommendations should come from your veterinarian,” Collins states. "But manage Johne's first and test second. Your veterinarian can help you determine which management practices work best for your situation.”

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