Concern about Johne’s in beef grows
That’s the language University of Wisconsin microbiologist Mike Collins uses to describe Johne’s, a secretive, chronic disease that seems to be gaining ground in beef herds.
After 25 years of researching and studying Johne’s disease, Collins says beef producers still tend to turn a blind eye to the possibility they may be either buying, selling or raising infected animals.
“Johne’s disease is primarily seen in dairy cattle. About 68% of our country’s dairy herds are infected,” Collins says. “By contrast, a USDA survey found that about 8% of cow-calf herds are infected. The difference in beef and dairy herd infection rates is simply a function of husbandry differences; dairy confinement practices allow Johne’s to spread faster. However, not enough caution is being exercised in the beef cattle industry to prevent spread of the disease among herds.”
Calves are most susceptible to infection, but cattle are usually at least 2 years old when signs of Johne’s appear. After the bacteria is ingested, the organism quickly grows in the intestinal wall, causing thickening and inflammation. The animal becomes unable to absorb nutrients. Proteins and electrolytes from the body begin leaking into diarrhea fluid.
Duane Pankratz, a veterinarian from Freeman, S.D., and a black Angus producer, says Johne’s awareness in South Dakota has improved, yet many producers hesitate to invest in testing.
“I encourage producers testing for BVD [bovine viral diarrhea] or brucellosis during annual treatment programs to also run the Johne’s blood test,” Pankratz says. “We test annually at a cost of about $10 per head. If there’s any reason to believe an animal is infected, we have it tested by bacterial culture.”
Dale Grotelueschen, senior veterinarian with Pfizer Animal Health’s beef cattle veterinary operations group, says Johne’s long incubation period makes it difficult to diagnose without testing.
“Occasionally calves can be infected before they’re born,” Grotelueschen says. “Cattlemen would benefit from consulting with their veterinarian on how to best manage Johne’s in their herd.”
Collins and Grotelueschen say cattle are transported more often than in years past, and those situations can put an entire herd at greater risk.
“Many livestock shows require testing for certain disease agents, so infection risks are low,” Grotelueschen says. “The fetus of a pregnant cow is probably most at risk. I advise exhibitors to isolate animals for about three weeks after a show to monitor for signs of illness.”
Collins emphasizes the importance of using the right test for the right reason. Blood samples known as ELISA offer herd screening, but a bacterial culture or DNA probe, called a PCR test, are the only tests that verify Johne’s presence. Yet the answers these tests give aren’t always clear.
“[Recently] a producer who sold an expensive bull called,” Collins says. “The bull was tested by ELISA and found to be positive. He then completed a PCR test on a manure sample. The PCR was negative. But the buyer no longer wanted the bull. He was nervous about the possibility of bringing Johne’s into his herd. The seller felt strongly the PCR test proved his bull was not infected. From the seller’s perspective, if he had used the PCR test initially, he wouldn’t have had a problem. From the buyer’s perspective, it was better to play it safe and require the bull to be negative by both ELISA and PCR.”
Still, testing and culling infectious cows is an important herd control tool.
Destruction of Johne’s bacteria on contaminated surfaces can be accomplished with soap and water followed by a “tuberculocidal” disinfectant.
Pankratz and Collins note that scientists and commercial companies are conducting research to improve Johne’s testing. However, current testing methods are adequate for diagnosing and managing the disease.
“Bacterial culture can take as much as three months, which is a drawback,” Pankratz says.
“PCR offers the same accuracy and can be done in under a week,” says Collins. He stresses that where Johne’s is concerned, prevention pays. Beef herd owners should only buy herd replacements from test-negative herds. It’s well worth the investment.
Sorensen writes from Yankton, S.D.
This article published in the April, 2010 edition of BEEF PRODUCERS.