Johne’s Disease: Going, Going, Gone?

12/15/2012 7:00 AM

Federal funding for the Johne’s Disease (JD) program has been in decline for a number of years, resulting in states receiving little to no federal money to support their programs. The Animal and Plant Health Inspection Service (Veterinary Services) is also moving to a commodity-based structure, meaning that any activities and support for the Johne’s program will be part of the general cattle health program. At least in the foreseeable future, it is unlikely that Johne’s will be a top priority disease issue for the agency.

So does this mean that the JD problem is solved? Has Johne’s been reduced to such a low level that there is no longer any concern for this disease? Hardly. In fact, a recent publication estimates that between 82 and 99 percent of all dairy farms in the U.S. with 30 or more cows have the bacteria that causes Johne’s Disease (Mycobacterium avium ssp. tuberculosis, a.k.a MAP) present on the farm. So the problem appears to be as widespread as ever — if not more so.

The news about diagnostic tests and vaccines to help control JD is also not (yet?) overly promising. Diagnostic tests have improved over the years, but they remain imperfect (especially for infected animals that test “negative”) and relatively expensive (especially fecal culture and PCR). And although efforts are being made to develop better, more effective vaccines, it is likely that the availability of any such vaccine is still years in the future.

Does the lack of funding, the widespread nature of the problem, the imperfect tests, and lack of an effective vaccine, mean that we should give up on Johne’s? Not at all. The goal for most infected herds should be to eliminate virtually all clinical JD, and achieve/maintain only a very low level of infection. The good news is that it appears that this is quite doable. By contrast, completely eliminating/eradicating MAP infection from a herd is a very difficult-to-accomplish goal, and this may not be a realistic, or even economically viable, option for most herds.

There have been a number of recent studies which have examined the efficacy of various management practices at reducing the transmission of Johne’s within a dairy herd. Studies from Minnesota, Wisconsin, and Canada are among those that suggest that implementing management factors to reduce calfhood exposure to the MAP bacteria is crucial to reducing Johne’s Disease. Our experience working with a number of infected herds over multiple years here in Pennsylvania is consistent with these studies.

So what are these critical management practices? One of them is reducing the exposure of calves to manure in the calving area. This can be accomplished by ensuring that the pen is kept extremely clean at all times, and, ideally, only having one cow in a maternity pen at a time. Another practice is to remove the newborn calf from the maternity area immediately to avoid contact with adult cows or their manure. Although this can usually happen more quickly (less than 30 minutes) in large herds with round-the-clock maternity area personnel, it should also be the practice in small- and medium-sized herds (less than 1 to 2 hours). If MAP testing is routinely carried out (eg. milk ELISA), calving pens can also be designated for test-positive and test-negative animals.

What the calves are fed is also very important. Colostrum should be fed from cows that have at least one negative MAP test, and/or the colostrum should be properly heat-treated prior to feeding. Excess colostrum from test-negative animals can be frozen for later feeding to calves born to test-positive dams. Pooling of fresh or frozen colostrum from multiple cows is discouraged. In extreme situations feeding of colostrum replacers might be justified. Similarly, if milk replacer is not being fed after colostrum, pasteurized whole milk should be offered. Manure contamination of colostrum or milk should be carefully avoided.

Testing of cows using milk, blood, or manure MAP tests can be a useful addition to a herd management program, but should not be considered as the first, or only, practice to be implemented. Simply removing test-positive animals without implementing other management practices is a very, very slow — and usually ineffective — way to make progress at controlling JD in a herd.

In general, animals that have a “high-positive” test result are much more likely to develop clinical disease than low-positive or negative animals, and are much more likely to have their calf (eventually) test positive. So these animals should be sold for slaughter rather than be allowed to calve again on the farm. Although it is probably most economical not to cull cows just because they are low’ or moderate’ positives, these animals need to be handled as more infectious’ than their test-negative herdmates. And remember, some infected/MAP shedding cows will test negative, so don’t let your guard down with test-negative animals.

These are just a few of the critical areas to consider when reviewing your JD management plan. You can visit www.jdrap.org to try out an online, interactive Johne’s risk assessment tool. You should also discuss your Johne’s program with a knowledgeable veterinarian who knows your farm and management practices and can offer some tailored, professional advice and suggestions.

Source: Penn State Extension


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