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Due diligence with Johne’s disease

Have animals tested and cull infected cattle early

Johne’s disease (pronounced yo-knees) as we all know, is the paratuberculosis organism that in livestock can cause diarrhea, weight loss and eventually death from starvation or condemnation at slaughter due to emaciation.

Animals that test positive, provided they are still in good body condition, can be slaughtered for human consumption, as the disease does not affect meat quality.

The disease has a very long incubation period of at least two years. Transmission is through oral contact with fecal material and most often comes from a young calf nursing its infected mother.

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Johne’s is seen in many cloven-hoofed animals including dairy and beef cattle, bison, elk, small ruminants and camelids. It’s most commonly detected in four- to six-year-old cows, which means by the time it is found it can pass through a few generations. Clinical cases are the biggest problem, but Johne’s also affects the sale and export of purebred cattle.

New additions to a herd are a possible source, making it difficult to figure out where the disease originated.

Testing in the past was very inaccurate but the current fecal PCR test rarely misses a case as the test can identify DNA of that organism passed in the manure.

Laboratories can even do a pooled test which means manure sent in from five separate animals is pooled at the lab. If no disease is detected then all five animals are cleared. However, if there is one positive in the five samples it will show up. Then those five individual samples are tested to determine which animal is positive.

Many research teams worldwide are working on Johne’s as it is a very important production-limiting disease and one we should always be on the lookout for when buying new animals.

The only required Johne’s test is for AI bulls going into stud. The dairy industry has a multi-tiered eradication standard it tries to achieve. Johne’s is more prevalent among dairy cattle because of their proximity to each other and usually greater exposure to manure produced by herd mates. With beef cattle generally being much more spread out for a good part of the year, there is a lower risk of the disease being passed between cows.

Manure management

The organism, under the right conditions, will last about a year in the environment so proper manure management is also critical to reduce transmission. Ideally, manure should be spread on grain land, not hay land or pasture.

If the disease has been identified, culling animals at the first sign of diarrhea but before serious weight loss is recommended. Also, any female offspring from the infected cow should be culled to reduce further spread.

Fecal testing is much more accurate today, but keep in mind there may be false negatives. These tests are often identifying cows that will eventually be positive because of the long incubation period but simply aren’t positive yet. The same applies when buying livestock to be introduced to the farm. It is important to ask for a Johne’s test, but if buying bred heifers, for example, because of the long disease-incubation period, it may not show up in a test.

If producers get a positive fecal PCR test, my advice is to cull as soon as possible. If a positive test involves a very valuable animal, the cow could be superovulated to collect embryos but kept isolated from the rest of the herd. Also, be very careful with manure handling and where it is spread. With superovulation and the way embryo washes are done, there is no risk of transmission of the disease by the embryos. This is helpful, especially for purebred operations.

What we can’t do is shoot and drag really thin cows with diarrhea to be buried. They need to be culled early when they still have value. If Johne’s is suspected it is important to have cattle tested. I know one producer who bought about 25 cows from another farm and one of the cows developed diarrhea. It was tested and culled. Since it was a positive the obvious thing was to test the remaining 24 cows and he found three more positives, which were sold. I would recommend he test the smaller group again for a couple of years in case they become positive so as to really nip his problem in the bud.

One thing you don’t want to do is bury your head in the sand. Be diligent, make some wise decisions on testing and get the herd disease level down to as close to zero as possible.

As mentioned earlier, the environmental pooled samples can be tested but there is a possibility of missing disease detection. Ideally, go directly to the ones you are worried about and have them tested. If we all work together and at least keep an eye out for this disease the incidence in the Canadian beef herd can be kept as low as possible.

For more details on Johne’s Disease visit the Beef Cattle Research Council website.

About the author

Columnist

Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.

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