Johne’s lurks under the radar in beef sector

Cows that lose weight but still have good appetite might have Johne’s and should be tested.  |  Heather Smith Thomas photo

Johne’s is a sneaky disease that most cattle producers don’t notice until it is well established in a herd.

It doesn’t show up until an animal has been infected a long time and then starts to lose weight and eventually has diarrhea.

Tests for the disease won’t show anything until the animal is in those later stages.

For years, beef producers were unaware of this disease or thought it only occurred in dairy cows.

Dr. Steve Hendrick of the Coaldale Veterinary Clinic in Coaldale, Alta., did his vet school graduate project on this disease and continues to research it.

“We don’t know how high the incidence of Johne’s might be in beef herds — possibly less than one percent, in terms of animals testing positive — but when it appears in a herd, it can be a huge disaster,” he says.

The main signs are diarrhea and thin cows but these animals have good appetite and do not appear sick.

“If it’s an older cow, a person might think she has bad teeth. If a cow has loose manure you might think it’s from lush green grass. With dry conditions, however, it would be easier to tell if a cow had diarrhea.”

Liquid feces from a cow with Johne’s can contaminate a lot of feed. Some cows are super shedders and if producers have one in their calving pen, most of the calves will be exposed to the disease.

Dr. Karin Orsel, veterinarian at the University of Calgary, says this disease has been on the radar of the dairy industry a long time, but is also a problem in beef cattle.

“Yet when we submitted a grant proposal to look at it, the beef industry told us, ‘that disease is not a problem for us.’ If a person doesn’t look, they won’t find it. Dairy farmers can enrol in the Alberta Johne’s Disease Initiative but we get a lot of phone calls from beef producers wondering if they can enrol or send us samples for testing. It is definitely present in the beef industry, but except for Dr. Hendrick’s early research, and that of a graduate student, Dale Douma, nobody has looked at it in Canada. We need research dollars to do this,” she says.

Ten years ago, the United States National Johne’s Disease Demonstration Herd Project evaluated losses associated with Johne’s disease in cow-calf herds. Findings were based on blood tests and fecal cultures for the cause — Mycobacterium avium paratuberculosis.

“There was considerable loss in weaning weight in calves from dams that were positive for Johne’s. Infected cows lose body condition, affecting milk production,” says Hendrick.

“It upsets me when purebred producers ignore Johne’s, selling animals that other people are taking into their herds,” he says.

“I have worked with a couple breeders with Johne’s, however, who spent time and money to clear it from their herds by testing and getting rid of all positive animals and trying to minimize contamination on pastures. They stopped selling seedstock for five years, and worked through it — to the point that we found no positives, no sign of any disease there anymore — and now those producers are selling seedstock again,” he says.

“People realize there is very low risk in buying an animal from these herds.”

Some breeders don’t want to admit they have a problem, however, because they think this would turn away customers. But if they’ve gone through testing and culling, their herds are safer to buy from than an untested herd.

If an infected animal is introduced to a herd, all animals are at risk if they come into contact with manure containing the bacteria. Contaminated feed and water are typical routes of transmission. Baby calves are highly susceptible because they may nurse a dirty udder.

Johne’s is most common in dairy cattle because they are generally more confined than beef cattle. “Most dairy cows, on average, are not still in the herd past about five or six years of age, however, and may not show signs yet,” says Hendrick. “Beef cows may stay in the herd until they are 12 to 18 years old. Animals infected as calves typically break with clinical signs in three to five years, but they’ve been shedding bacteria well before that, and infecting other animals.

“If you give cattle enough exposure, at any age, which they would get in a confined, wet environment such as a calving lot, older cows probably become infected along with the calves, but it’s mainly the young calves that get infected and later cause grief,” he says.

In a beef herd, cows may break with clinical signs before they are old enough to cull.

“We know it’s there because we test a lot of beef herds,” says Orsel. “I think the reason it is not on the radar of the beef industry is because it mainly shows up in older cows. You’ll never see it in the feedlot industry; it is not an issue for animals that young. They are slaughtered before it can become established, and there is no health risk to humans who consume the meat. Thus it is mainly a ranch disease — in cow-calf herds,” she explains.

When people gather cows in the fall and see one that has lost weight and looks rough, they usually sell it. They never check to see if it has Johne’s, so they don’t know if it has been spreading the pathogen in its feces, infecting other animals.

Biosecurity is the best prevention.

“In our observation of herds with Johne’s, intensive grazing is a risk factor. They tend to have more positive animals,” Hendrick says.

If a large number of cattle are confined in small areas of pasture, there’s more risk of ingesting fecal material. Intensive grazing is an efficient way to use grass and increase stocking rates and pasture health, but producers want to make sure they don’t bring in an animal that could infect their cattle.

Since young animals, even if they’ve been exposed, won’t be shedding bacteria yet, producers might get away with bringing in yearlings for grazing; they would be less risk than bringing older animals that might spread the disease.

“It’s rare to see an animal less than two years of age with clinical signs, so if cattle are coming in as yearling stockers and only grazing a few months in summer, there is less risk than with older cattle,” Hendrick says.

He has seen herds where producers set themselves up for trouble. In one herd, the rancher had a pen next to his calving ground where he wintered a cow that wasn’t doing well. She became thin and he wanted to feed her more. Then during calving he put all his cows through that pen. A few years later he had a problem with Johne’s.

If a producer can get his cows to calve on grass and keep animals dispersed, there is less risk for contamination and infection.

“Whatever a person can do to reduce scours (clean calving areas, moving the calving herd to clean pastures, etc.) will also reduce risk for Johne’s, just by reducing exposure to a lot of fecal material,” he says.

Ranchers need a quarantine area for suspicious cows. Also be cautious about bringing home a dairy calf to raise on a beef cow that lost hers.

Many problems are purchased. Dairy calves don’t present a risk as calves, but if you keep any of them longer, this could be an issue later,” says Hendrick.

“There are many diseases in which a good vaccination program can help with prevention, but there is no vaccine for Johne’s allowed here,” says Orsel. “There is a vaccine in Australia but it interferes with tuberculosis testing.”

Samples from blood or manure can be tested in a lab. In the past, the only way to test was to try to grow a culture of bacteria from a manure sample, but today a PCR test gives faster results.

“It takes at least eight weeks to grow the culture and may take 16 weeks before you know the results from a culture,” says Hendrick.

With a PCR test the results usually come back within a week. Both tests have similar accuracy, but the PCR test is more expensive.

It is important to check it out, rather than just culling thin animals. Producers wouldn’t want to sell a cull cow that might spread the disease to someone else’s herd.

“If you buy a young bull, he will test negative, but a negative test at that age doesn’t mean anything,” says Orsel.

“He may be incubating the disease and test positive when he is older. A negative test doesn’t mean much, but a positive test is clear. You should respond to that, and do something about it,” she says.

“Some producers do herd-level testing. If you know that the entire herd tests negative, you can be much more comfortable about buying a bull or females from that herd. If the herd of origin has been testing, and never had an animal test positive, I would feel comfortable buying a young animal with a negative test; it is very likely a negative animal. But if you buy without knowing the herd status or without any test or disease history, there is a chance that you’ll buy Johne’s and bring it to your herd.”

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