Deer can get either sheep or cattle strains of Johnes disease. The disease can take up to five years to express itself as clinical disease but young deer can die at 8-15 months of age with up to 10-20% of a group affected and dying. Johnes disease causes wasting, generally with a scour, and death.
Johnes disease can also interfere with the skin Tb test causing false positive reactors and causes lesions to be found at the works resembling Tb. This results in carcasses being detained until Tb has been ruled out.
The key to Johnes control at this stage is detecting and culling infected animals early to limit their shedding of Johnes bacteria onto the pasture. In sheep, farmers have the option of being able to vaccinate against Johnes, and this vaccine has proven to be very effective in decreasing the level of disease, in vaccinated flocks. However, it interferes with the skin Tb test so is not an option for use in deer (or cattle) at this stage. But vaccination of sheep on a mixed deer property could be an option to dilute pasture contamination if vaccinated sheep are run at times on deer pastures.
Stress also pays a role in the progress of the disease with the disease more likely to occur in younger animals when they have been stressed. Thus attention to parasite control, trace element supplementation and good feeding levels will go a long way to limiting the disease in young animals.
What tests are available to detect Johnes infected animals?
In the past Johnes has been difficult to diagnose until late in the course of the disease, either by post-mortem and histology at the laboratory or by faecal samples or blood tests. New blood tests are being developed which are capable of detecting infected animals earlier in the disease course so they can be culled earlier. If you are concerned as to whether you have Johnes or about how best to deal with it in your herd, then please get in touch with Clutha Vets to discuss management options/tests for your situation.
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