South
Florida
Beef -
Forage
Program
"Article of the Month"
January 2000
JOHNE'S DISEASE
A CONCERN FOR FLORIDA CATTLEMEN
Patrick Hogue, Highlands County Extension Director/Livestock
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.
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Johne's Disease A Concern For Florida Cattlemen
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