Keep Johne's at bay

You may choose to milk that thin cow with diarrhea another month or two and then cull her. But can you afford to ignore the data and the long-term damage she's already done to your dairy?

That cow probably has Johne's (pronounced YO-nees) disease. She's already costing you more than $200 a year, mostly in lost milk production. And she's exposing other animals to this untreatable, chronic infection.

According to a 1996 survey conducted by USDA's Animal and Plant Health Inspection Service:Veterinary Services (APHIS:VS), 22% of the herds had two or more positive ELISA tests or one positive test with at least 5% of the herd showing clinical Johne's disease symptoms. Smaller herds—less than 100 cows—tested positive one out of five times. Forty percent of the herds with 300 cows or more had two or more positive tests or one positive test with at least 5% of the herd having clinical signs.

Because current Johne's tests don't detect every infected animal, scientists say finding one positive animal is the tip of the iceberg.

"For every clinical animal present, there may be from 10 to 25 subclinical infected animals in the herd," says Leslie Bulaga, APHIS:VS area epidemiology officer, Robbinsville, N.J. "If a herd of 100 milking cows has had two clinical cases of Johne's in the past year, there are probably 20 to 30 other cows infected."

If you truly have a closed herd where you calve and raise your own heifers and don't use off-farm bulls, Johne's probably isn't high on the priority list. The USDA survey shows that more than 70% of the U.S. herds do not have Johne's. However, be aware that Johne's is on the front burner for two reasons: international trade and public health.

As major diseases such as tuberculosis and brucellosis are eradicated, diseases such as Johne's and leukosis are more important in global trade, Bulaga says. Australia recently started a Johne's control and certification program and is using negative herds as a marketing edge in Asian markets. Sweden and the Netherlands are also working on Johne's control.

The public health concern hits closer to home. Some scientists believe the agent that causes Johne's, Mycobacterium paratuberculosis, may play a role in Crohn's disease, a chronic intestinal disease in humans. To date, some research shows a link between the two diseases.

"If Johne's is a concern, and I think it should be, you first need to determine your herd's status," says Charles Elrod, Cornell University senior Extension associate. "I would consider some kind of testing program so I would know how aggressively to manage it."

Before you begin drawing blood samples, Elrod advises that you think through the ramifications of a testing program and discuss them thoroughly with your veterinarian. Key questions to consider include: Why test for Johne's? How will a Johne's control or prevention plan impact our business? What will we do if animals test positive? How will we manage the positive animals on the dairy?

"Each farm has different restraints— physically, financially, with labor—to manage the problem," Elrod says. "You need to find out the strengths and restraints of your resources."

For example, say you've decided to be proactive with Johne's since you bought cattle last year. You decide to screen 10% of your herd with the ELISA test. If the test shows a high prevalence of Johne's, you'll take fecal cultures on the whole herd to find out the herd's infection level. Then you can pinpoint those at-risk animals and manage them accordingly.

"The ELISA will give a good screen," Elrod says. "Then use the fecal test as a confirmatory test. The results of the two will vary a bit. Each one picks up different animals."

Both tests have their limitations. They cannot detect Johne's in cattle under 2 years old. They identify some positive animals and miss others, depending on their clinical or subclinical status. But when the tests find sick cattle, they are highly accurate. Compared to the fecal culture, the ELISA is cheaper ($2 to $5 versus $10 to $20 per test) and quicker (3 to 4 days vs. 16 weeks).

So why bother testing with these shortcomings? "We eradicated brucellosis and that test sensitivity is similar," Elrod says. "These are what we've got and they allow us to get started."

Getting started is half the battle. After you begin a control program in a Johne's-positive herd, it will take one to three years to eliminate clinical cases and reduce financial losses, Bulaga says.

"Complete elimination of infected cattle will likely take many years after Johne's becomes invisible in the herd. But it can happen," she says. "Preventative management practices must remain permanently in place to prevent reintroduction of infection to the herd."

A Johne's control program in a non-infected herd is a good long-term business investment. Those animals will provide a source of breeding stock and replacement animals for other herds, and help reduce the national prevalence of Johne's, Bulaga says.

One way to organize a control program is to design a flowchart, Elrod says. He developed the flowchart for this story, which shows high-, moderate- and low-risk management practices associated with Johne's.

"Write everything down and explain it to all farm personnel so everyone will understand where the risks are and what the benefits will be," he says.

Be sure to include a protocol for purchasing cattle. Before you buy, Elrod suggests that your veterinarian and the seller's veterinarian discuss the health of the animals for sale.

"They can talk more honestly so the seller's veterinarian will understand the buyer's concerns," he says. "This might preclude troubles later. Questions will get pointedly asked and they can't plead ignorance later."

You'll also want to review the animals' health, production and mastitis treatment records with your vet before you buy. Try to see them on the seller's dairy and observe herdmates and management. Do what you can to minimize risk, Elrod says. The more information you have, the better business decision you will make.

Sidebar:
Voluntary certification program on the way

Momentum is gaining for approval of a two-track voluntary Johne's certification program.

A subcommittee of the National Johne's Working Group, under the direction of the U.S. Animal Health Association's Johne's Committee, is proposing a four-level program for herd certification. Compared to the unsuccessful herd certification program approved by USAHA in 1993, this one will be more flexible and lower in cost, say subcommittee members.

Producers may enter the proposed program by either a standard- or fast-track method. The standard track allows producers to gradually increase their investment while increasing assurance that their herd is Johne's-free. It will take at least three years and four tests to reach Level 4 (99% confidence level that herd is free of Johne's). Total cost for the average 100-cow herd: $3,100, including vet costs.

The fast-track method costs more upfront, but allows producers to enter the program at Level 2 (95% confidence) with a certification statement by the herd owner and an approved accredited veterinarian, state or federal animal health official stating that there has been no clinical evidence or laboratory diagnosis of Johne's disease on the farm during the last five years. Fast track will allow herds to reach Level 4 in two years with three tests. Total cost for the average 100-cow herd: $1,700, including vet costs.

The program will be presented for approval at the USAHA meeting in November.