Bovine Johne’s Disease
About the disease
Bovine Johne’s disease commonly referred to as BJD (or Ovine Johne’s Disease in Sheep and Goats) is a bacterial infection currently uncurable that effects the intestine causing serious wasting and chronic diarrhoea in Australian cattle. It has also affected goats, camelids and deer in Australia.
What Causes BJD?
The cattle strain of the bacterium, Mycobacterium paratuberculosis, is known to cause BJD. This strain will live mainly in animal intestines, but can also survive outside the beast for several months. (The sheep strain of M. paratuberculosis has led to causing ovine Johne’s disease (OJD) in both sheep and goats, and has even crossed over into some cattle herds.)
The infection of the M. paratuberculosis bacterium causes a reduction of absorption of nutrients due to the thickening of the intestinal wall. The infected animal will loose nutrients from grazing and feeding and can eventually starve to death.
BJD is the more common infection in cattle but cross-infection between animal species can occur. Scientific literature reported cattle infected with OJD, probably as a result of co-grazing with OJD-infected sheep.
BJD bacteria are can live for a long time in the environment outside of animals. There has been research in Australia’s southern states showing that increased temperatures, heat and sunlight do destroy BJD. Around 90% of the bacteria die in 6 weeks under normal summer conditions. However, in more moist and shaded conditions, BJD bacteria can survive for over 12 months.
BJD infected Cattle will excrete the bacteria in their manure. This can then contaminate pastures as well as watercourses, allowing the infection to spread across the herd and into other animals sharing the same paddocks, yards and environments.
Once a herd is endemically infected, the eradication of Bovine Johne’s Disease is extremely difficult.
What are the Clinical signs and symptoms of BJD?
Cattle with BJD have commonly been infected as calves. They will not however, show any symptoms for a number of years and can begin to excrete the BJD bacteria before developing any clinical signs.
Infection rate among a herd may start low, however if BJD remains uncontrolled, the rate of infection can increase rapidly. Not only does the risk of infection rate increase, but also visibly sick and unwell animals can lead to animal welfare issues with an onflow effect of the reduction in enterprise production.
The most common signs of BJD are:
- chronic diarrhoea (scouring)
- wasting
- death from malnutrition.
Some cattle may not be inflicted with all of these conditions but simply will not reach their full production potential.
First signs of BJD in dairy cattle are:
- a drop in milk production
- then weight loss, and
- scouring
This will occur despite adequate feeding of the cattle. A condition called ‘bottle jaw’ (a soft swelling of fluid under the lower jaw) can also be seen in the early stages.
The most likely first sign of BJD in beef cattle can be weight loss, with or without concurrent scouring.
Why are BJD prevention and controls important?
If BJD is introduced into a cattle herd, the disease can severely impact on a business, especially when the herd is used primarily for breeding enterprise. A seed stock producer’s reputation can be damaged if animals sold are subsequently found with BJD infection.
Bio securities practices are the best prevention and considered the most sound investment due to the high level of difficulty in eradicating BJD from an infected herd.
BJD can enter the herd when infected animals are introduced through either purchasing or agisting infected stock.
Australia has a low prevalence of BJD in beef herds – which has been noted and continued to be recognised on the international market. Most parts of Australia along with the majority of Australian beef cattle herds are known to be free of BJD. It is therefore important that you invest in a program that continues to protect this desirable animal health status and reduces the risk of disease spread.
If no controls or action is taken to maintain low levels of infection in beef herds in Australia, the reputation of Australia as being Taking no action to control and maintain the very low levels of infection in Australian beef herds could undermine Australia’s reputation as an exporter of premium beef products.
While scientific literature has explored a possible link between Johne’s disease in cattle and Crohn’s disease in humans, the evidence does not support the relationship, but it is prudent to manage Johne’s disease as a precautionary measure.
Several of Australia’s major markets and competitor countries require certification for BJD status and are implementing BJD control programs, so infected herds could be excluded from particular markets that require certification of absence of disease.
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