Johne’s disease causes chronic diarrhea with severe weight loss in cattle, bison, small ruminants, such as sheep and goats, and camelids.
It may last for months, is invariably fatal, and is caused by a paratuberculosis organism similar to tuberculosis. As a result it has a long incubation period of at least two years.
Calves younger than three months are the most susceptible to contracting the disease. Heifer offspring from affected cows should be culled because they will most likely show signs later in life.
With this disease, cattle maintain a voracious appetite but a thickening of the small intestine prevents nutrients from being absorbed so weight loss is dramatic.
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In winter, a large manure ball can be frozen to the tail.
If you suspect this disease, it is imperative to have the animal examined.
Johne’s disease is seen around the world. The concerns are two-fold: the economic losses associated with cows having decreased production or having to be culled; and the human health concern.
There have always been concerns about Johne’s close resemblance to human Crohn’s disease. Recently, scientists isolated the same paratuberculosis organism from a Crohn’s patient as that causing Johne’s.
Johne’s spreads primarily by way of the fecal-oral route. Transmission through milk or transplacentally has also been demonstrated. The organism has also been isolated from bull semen.
Control strategies focus on good manure management, culling appropriate animals and herd testing where necessary.
The organism can survive in moist manure packs for up to a year and is resistant to freezing. Survival in soil or water is greater than one year.
Desiccation kills the organism so harrowing pastures iseffective.
Manure should be spread on grain land, not on pasture or hay land. Don’t use the same front-end loader for feed and manure without proper disinfection in between. All calving areas should be disinfected with a phenolicÐbased disinfectant whenever cleaned. Keep feed bunks and watering bowls clean of manure.
Always buy bulls and replacement cattle from sources where herd health status is known. Screenembryo transplant recipients for Johne’s.
Renting bulls and in some cases pasturing in community pastures has the possibility of increasingcattle exposure.
We are fortunate in Western Canada that our cattle are spread out on pasture for most of the year, minimizing the exposure that confinement brings.
Culling known cases immediately reduces their shedding and if done early, before severe weight lossoccurs, they will pass slaughter.
Cattle with severe weight loss would still qualify under the BSE testing program and should be disposed of that way.
Review records and cull recent heifer calves because they are highly likely to contract Johne’s.
Experts talk about the iceberg theory with Johne’s because for every clinical case in your herd there are probably at least 10 more incubating the disease.
The worst scenario I have encountered was a 20-30 head herd that was experiencing one to two clinical cases a year. Depopulation, thorough cleaning and disinfection was the only way to eliminate it.
In the future, trading partners may require Canada to prove it has a low incidence in most herds.
Alberta government veterinarians have a volunteer program, involving blood testing and fecal pooling, that certifies herds with disease freestatus.
In 1998 the Alberta government, in co-operation with private practitioners, conducted a sampling program that found 4.4 percent of herds had at least one positiveanimal, based on fecal culture.
In herds we deal with, I have found that we can keep the disease suppressed by isolating and then eliminating clinical cases as quickly as possible, removing heifer offspring and following proper manure management.
From a human health aspect, we must insure a safe product to consumers at home and abroad. These fairly simple management changes will help.
Roy Lewis is a veterinarian practising in Westlock, Alta.
