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HUNTIN' DAYLIGHT - SLOW BURN

Wes Ishmael

If Al Gore ever decides to go to one of his infamous D.C. Halloween parties decked out as a bacterium, he ought to go dressed as Johne's disease. After all, both can filch jingle out of your pocket before you know they're in the same county, and both can get you in a heap of trouble, fast.

For the record, don't feel like the Lone Ranger if you're more familiar with Gore than Johne's (pronounced Yo-nees). Even though the disease has been around since dirt was a baby, most beef producers have never heard of it. In fact, according to a study conducted by the National Animal Health Monitoring Service (NAHMS), 92.2 percent of beef producers are either unfamiliar with the disease or only recognize the name of it.

One reason is that lots of folks pigeonhole it as a dairy disease. And, the dairy industry is eaten up with it. When NAHMS conducted a dairy study in 1996 it found at least 20 percent of the nation's dairy herds are infected with the disease; 40 percent of the herds with 300 head of cattle or more are infected with it. NAHMS estimates the disease costs the dairy producers with infected cattle more than $200 for every cow in their herds, due primarily to decreased milk production and premature culling.

But, the disease is alive and well in beef herds, too, albeit at a much lower documented level. In 1997, NAHMS took the first national snapshot of the disease in beef herds, testing 10,372 cows from 380 herds in 21 states. Of those, only 0.4 percent tested positive. Infected animals came from 30 different herds; 7.9 percent of those studied.

Before you start doing cartwheels, though, keep in mind the sampling protocol of the study was designed to identify herds with a minimum 10 percent infection rate. And, only four percent of the herds tested were seedstock operations. That's significant, because according to veterinarian experts, more intensely managed and confined operations like dairies and some seedstock operations are at more Johne's risk than those where cattle have more breathing room. And that has everything to do with how the disease works and is transmitted.

How it Works

In a nutshell, Johne's (also called paratuberculosis) is an infectious bacterial disease caused by a distant relative to the bacterium that causes tuberculosis. It primarily affects the intestinal tract where nutrients from feed are absorbed. As the infected animal fights the bacteria, immune response causes the intestinal lining to thicken, which ultimately leads to reduced nutrient absorption and diarrhea.

Although the primary mode of disease transmission is fecal-oral, the bacteria can spread in-utero and through the milk of infected cows, according to John Maas, DVM, extension veterinarian for the School of Veterinary Medicine at the University of California-Davis. In fact, he says, “Infected cows showing clinical signs of Johne's transmit the agent to the unborn calf 20-40 percent of the time. For infected cows not showing clinical signs in-utero transmission occurs about eight percent of the time.”

As well, the jury is still out on whether the Johne's microbe can be transmitted via semen. And, Maas explains the bacteria can be passed between all ruminant animals. So, at least in theory, that means infected deer, sheep and goats can also pass the infection on to cattle.

And, Johne's bacteria are tougher than boot leather baking in the Death Valley sun. They can live in the ground, even in water, for up to a year. Plus, Don Hansen, DVM, an extension veterinarian in the School of Veterinary Medicine at Oregon State University explains Johne's has a long incubation period. Cattle can be infected for years before they exhibit any clinical signs. In fact, many cattle won't exhibit any clinical signs until they're at least two years old. Instead of a disease where a bunch of infected cattle break with symptoms at the same time, the clinical signs of Johne's show up in a few animals from time to time over the long haul. All the while, infected animals are shedding the bacteria in their feces.

With this in mind, Hansen and other animal professionals believe Johne's must be addressed as a whole-herd health challenge, rather than fighting it one animal at a time. Besides, if you're normal, you'll probably mistake Johne's for some other disease the first time you see it.

“Diagnosing the clinical signs of Johne's is relatively easy. Primarily, infected animals will exhibit weight loss and diarrhea,” says Maas. “But, many diseases cause the same symptoms, including parasites, BVD, copper deficiency, liver failure, founder, selenium deficiency, and Salmonellosis, to name just a few.” In advanced cases, he explains cattle will develop bottle jaw. So the only way to know for sure Johne's is behind the symptoms is to test the cattle, with the realization current Johne's tests are a long ways from foolproof.

Should You Test?

“It's a tough call,” says Maas. “Personally, I believe seedstock producers should be testing at some level.” At the very least he suggests producers utilize testing guidelines approved by the National Johne's Working Group (NJWG) and national U.S. Animal Health Association (AHA). In part, those guidelines recommend initially testing 30 females—second lactation and older—utilizing an ELISA (enzyme-linked immunosorbant) assay. Think of it as a blood test for the disease. Statistically, if all of those cows test negative you should be 85 percent sure that your herd is clean.

Although seedstock operations may be at more disease risk and stand more liability if they would happen to unwittingly trade infected breeding stock to someone else, the cost and effort of trying to clean up an infected herd should give commercial producers pause as well.

First of all, testing is neither cheap nor exact. For instance, the ELISA test is the cheapest at $4-$6 per head, and the quickest—results can be known immediately—but it will only identify about half of the infected cattle, and it can produce false positives.

Fecal cultures¾which detect the Johne's organism itself, rather than the antibodies produced through immune response detected with the ELISA test—costs approximately $15 per head. It won't yield any false positives, but it takes four months to get results, and it too will only identify about half of the infected animals.

Then there is the stigma of testing that producers are fighting in some states. Whether or not the disease is reportable—it is in some states and not in others—producers fear that if customers know they are testing it could be as devastating to their reputations as finding infected animals. In theory, the hope is that economics will drive the current voluntary testing programs ahead; if buyers start asking for test results, then producers of breeding stock wind up in the same boat of having to test without as much worry of discrimination because they are testing.      

On the other hand, before diving into a testing program, Hansen encourages producers to consider the ramifications of testing and to explore bio-security measures aimed at preventing the introduction and spread of the disease.

     

Prevention and Control

Up front, the bad news is that Johne's isn't something you can spray for or even effectively vaccinate against. A Johne's vaccine is available, but in states that allow it, the vaccine must be administered by a licensed veterinarian (and only with the state veterinarian's approval) to calves no older than 35 days. But it's no silver bullet. For one thing, it makes cattle test positive for tuberculosis and eliminates all Johne's testing options, except the more costly fecal culture. Besides, vaccinations can't eliminate the disease, only reduce the number of cattle shedding the Johne's organism. Given the challenges, some states don't allow Johne's vaccinations.

The good news is that the same bio-security practices that producers can use to prevent other infectious bacterial diseases, like anaplasmosis, also help prevent Johne's from entering clean herds and help control the disease in infected herds.

As an example, Maas explains, “The two factors that determine susceptibility to Johne's are age and the how much bacteria cattle are infected with.” By age, that means calves are most susceptible. So, the sooner they are moved out of calving areas, the less exposure they have to fecal contamination. As well, the oral-fecal mode of transmission means producers can reduce risk by feeding cattle off the ground away from feces. Likewise, if possible, producers should consider letting cattle drink only where they can't also wade and defecate. And in the case of twins and orphans, cleaning the teats of cows used for colostrum can reduce risk.

Of course the easiest way to prevent the introduction of Johne's to a clean herd is by not bringing in any animals that are infected with the disease.

Maas says, “There are enough good seedstock programs out there that buyers can not only be concerned about the genetics coming into their herds, but also the diseases that may be coming with them.” That's why he encourages both seedstock and commercial producers to ask about the Johne's status of the herd, whether they're buying bulls, females or even semen.

“The bottom line for commercial producers is to do the bio-security things at home, and buy cattle with an eye on preventing the introduction of Johne's and other infectious diseases,” says Maas. “For the seedstock producer, the bottom line is that you don't have to be part of a Johne's certification or eradication program, but you're competing with those who already are.”

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