Johne’s disease affects beef cattle, as well
Paratuberculosis in cattle is a slowly progressive disease that doesn’t show up with clinical signs until an animal has been infected for a long time – and at that point it is termed Johne’s disease, with diarrhea and weight loss.
Dr. Steve Hendrick, Western College of Veterinary Medicine, University of Saskatchewan, did his graduate work on Johne’s. “This disease is most common in dairy cattle, primarily because they are more confined. Most dairy cows may not be in the herd past 5 or 6 years of age, however, and may not show clinical signs yet by that time. Beef cows, by contrast, may stay in the herd until they are 12 to 18 years of age. I have seen a 12-year-old cow with Johne’s disease, and I doubt she got infected as a baby calf; she would not have lived that long. Animals infected as young calves typically break with clinical signs in 3 to 5 years. They’ve been shedding bacteria well before that, and infecting other animals,” Hendrick said.
“If cattle get enough exposure, at any age, such as in a confined wet environment like a calving lot, some of the cows will probably become infected along with the calves. In the dairy industry they don’t last long enough for that to be a problem. It’s mainly the young calves that get infected and later cause grief,” he said. In a beef herd cows infected later in life may break with clinical signs before they are old enough to cull.
Cows with Johne’s don’t produce as much milk as uninfected cows. Dr. Allen Roussel (Texas A&M University) and a team of researchers are involved in a study looking at the effect of this disease on weaning weights in beef herds – comparing calves from dams testing positive for Johne’s with calves from uninfected cows. “Bikash Bhattari is the PhD student doing this study, funded by USDA. We used data from the US National Johne’s Disease Demonstration Herd Project, which compiled a great deal of data over a 6-year period, with demonstration herds in 18 states,” Roussel said.
Bhattari looked at differences in 205-day adjusted weaning weights of calves from cows that tested positive in fecal cultures, and cows with a strong positive serum ELISA blood test, compared with calves from test-negative cows in those herds. “It turned out to be somewhere around 60 pounds and 50 pounds less, respectively. This is a substantial loss, in calves from cows that are either shedding bacteria (in feces) or high positive on the blood test. These are cows in late stages of infection and dropping off in milk production even though they may not yet be clinically apparent. They may not have diarrhea yet, nor substantial weight loss and may not look sick,” Roussel explained.
“The important thing, to put this into perspective, is that we find a lot of beef herds that have a low prevalence of Johne’s, and some with high prevalence. I have spoken with beef producers and veterinarians in the upper mid-West who concentrate their herds at calving time because they calve early, and some of these herds have high prevalence. Here in Texas where most cattle are out on pasture year round they tend to have low prevalence,” he said.
In western states many herds are closely confined at calving time, calving early so they can be calved and bred before they go to summer range. “I talked to a cattle veterinarian in Montana who had a client with a substantial problem, and I have seen this in the Dakotas and Nebraska as well. There may be more herds with higher prevalence in northern states where cattle are confined for early calving than in places like New Mexico, southern Colorado or most of the Southeast. Most of the southern cattle are more spread out the entire year,” he said.
“If a herd has a high prevalence, there are more calves weaning light. If you have low prevalence, there are only a few calves weaning light. The economic significance is much less and you have to think about how much you can afford to pay for testing and control within the herd,” said Roussel.
“From a national herd basis, there are probably fewer than 20 percent of beef herds infected. Thus the most important thing in a control program is to not get infected, taking biosecurity precautions to not introduce animals that might pose a potential risk. Since many of the cattle coming into various herds are purebred bulls, it is important that the purebred industry control it within their herds. Internal control and testing is probably more important for them, partly because the animals may be more intensively managed and confined, and also because they are more valuable. They are not worried about losing 60 pounds at weaning; they are worried about losing a very valuable animal prematurely or selling one to somebody and dealing with those consequences.” A seedstock producer doesn’t want to send this problem to customers’ herds.
Some traditional things stockmen have done without thinking about possible consequences – such as getting colostrum from a dairy, bringing home a dairy calf to graft onto a beef cow that lost her calf, or buying an older cow from a dairy to use as a nurse cow to raise orphan calves – can put their herds at risk. The biosecurity risks include not only Johne’s disease but also things like Salmonella, cryptosporidiosis, leukosis and other diseases that they may not have in their beef herd.
“For a long time people in the beef industry used Holsteins as embryo transfer recipients but now use more beef cows instead, because of the risks. Johne’s can be passed from an infected dam to the fetus before birth, and through milk and colostrum to the calf,” Roussel explained.
“Many control measures have multiple benefits. Most of the things you do to minimize spread of Johne’s disease also minimize spread of calf-hood diarrhea and other diseases. Johne’s is fecal-orally transmitted (cattle ingesting bacteria from feed and water contaminated with manure, or calves nursing a dirty udder). When you spread out the cattle and their manure, and reduce contamination, you not only minimize spread of Johne’s disease but are also helping prevent other problems,” Roussel said.
“I don’t think anyone intentionally sells infected cattle to someone else. They simply don’t know they have Johne’s disease,” said Roussel. Without testing, they may not know. This disease may have slipped into their herd without their knowing.
Hendrick said, “It upsets me when I’m working with purebred producers who ignore Johne’s, when they are selling bulls or replacement females that other people will be taking into their herds.” A seedstock producer has a responsibility to his customers, especially if he wants to have repeat customers.
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