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Johne's Disease - A Concern for Florida Cattlemen
January 2000
Patrick Hogue - Highlands County Extension, Director/Livestock Agent
Should Florida cattlemen be concerned about Johne's disease? Well, this a disease that every cattlemen should learn more about, particularly the signs and symptoms of the disease and how to prevent it to insure it doesn't enter their herds.
Johne's (pronounced yo-nees) disease is a chronic infectious intestinal disease of cattle and other ruminant animals caused by the bacteria Mycobacterium paratuberculosis. It is in fact also known as paratuberculosis. If the disease is left to it's own devices in a herd, it can wreak havoc on individual animals.
Johne's disease has a long incubation period, and if ti gets in to a herd, can spread dramatically before any cattle ever even show clinical signs or symptoms. Although it poses the greatest danger of spreading through dairies and other cattle operations that have animals more heavily confined, it can spread through any herd through its primary mode of transmission, which is fecal-oral contact. The bacteria that are excreted in feces can contaminate soil and water, and can survive over a year outside the animal body. The incubation period is so long, that cattle may not show the clinical signs for years after the initial infection.
Even when cattle do show clinical signs and symptoms of Johne's disease, they can easily be confused with those of other diseases or problems. The most common symptoms are long-lasting diarrhea and weight loss, even though the cattle have a good appetite. Some cattle will become unthrifty because of progressive weight loss and nutrient deficiency, however, others may only have chronic diarrhea, and rarely do they have an elevated temperature. This can present a real detection problem for most cattlemen here in Florida, because we may not see every cow every day or on enough of a regular basis to even detect if one or more animals may have chronic diarrhea. Since the signs of Johne's disease usually develop in animals one by one over a prolonged period, years sometimes, you would not see an outbreak of cattle with clinical symptoms. You may notice an increasing number of cows exhibiting weight loss and/or diarrhea over time, but would not see a massive outbreak like is possible with other diseases. There is speculation that because of the slow progressive nature of movement through a herd, that if it is present in Florida herds, we may be culling out the disease without even knowing we have it. Typically, cattlemen will sell unthrifty, poor doing cows as culls, so it is feasible that herds have Johne's disease and are eliminating them from the herd through culling and selection.
So how does the disease get in to a cow herd? Since the disease has been shown to spread principally from fecal-oral contact, it is believed that it must be brought in to a herd. Besides the evidence showing spread through fecal-oral contact, there are some studies that suggest that about one third of the cows in the later stages of the disease may transmit the bacteria to calves through colostrum and milk. These studies also suggest that possibly up to 40% of the cows in the later disease stages may also infect calves in the uterus. All of this, however, still points to herd infection coming from within the herd. From the evidence that soil and water can be infected with the bacteria, and that it can persist for long periods of time outside the animal body, it is feasiblely possible that cattle drinking downstream from, or drinking from a water body shared with an infected adjoining herd could contract the disease in this manner. However, there is no evidence to support that this has happened, and typically it is believed that most herds are infected by bringing in an animal that may have the disease, but is not yet showing any clinical symptoms. Therefore, the best way to insure you don't bring Johne's disease in to your herd is to either close the herd, or purchase test-negative cattle from a low risk herd.
Why is preventing and eliminating Johne's disease so important to Florida's cattle industry as well as the industry as a whole. First, it decreases herd performance and at some point in time could cause your culling rate to increase as the number of cows that enter the later stages of the disease increase. You could mistakenly increase you supplementation costs by trying to get cows back in to condition that are infected with the disease, and because their intestinal linings are thickened from the effects of the disease, they are unable to utilize nutrients as they normally would. Second, it increases the liability of producers selling breeding stock, whether they are selling purebred animals or commercial replacements. Third, there is a similar disease of humans called Crohn's disease that is also a chronic intestinal disease. Although scientific and epidemiological studies have not established any connection between the two diseases, one thing that we should have learned from BSE is that all it takes is the insinuation of a possible link to receive media attention to effect the opinion of the consuming public.
If you suspect you may have Johne's disease, or just want to play it safe, contact your veterinarian to establish assurance that you probably do not, or protocol for assessing your situation. There is a vaccine available, but it is not recommended for routine use in most herds. Use of the vaccine requires permission of the State Veterinarian, because it can interfere with TB testing as well as with Johne's testing. Vaccination of an infected herd can reduce the number of cows shedding the disease organism, but the spread of the disease will continue. The use of the vaccine can actually impede rather than help with Johne's disease management in many herds.
There is an excellent publication produced by the National Cattlemen's Beef Association entitled "Johne's Disease, Should You Be Concerned?" This publication is available from either the NCBA or Florida Cattlemen's Association, and is an excellent source of information about Johne's disease. Johne's disease is a threat to the cattle industry and one that needs to be taken seriously, and one of the best defenses for producers is information.