The following information can help you to protect your property and stock from OJD, and to minimise the impact of the disease on both you and your neighbours if your sheep are already infected.
What is OJD?
OJD is a wasting disease that can cause significant mortalities in sheep. It transmits very easily between neighbouring flocks and over long distances by movement of infected animals.
Sheep become infected by eating infected pasture, drinking water that is contaminated with Johne's bacteria or in utero (before birth).
OJD has a long incubation period, usually more than 2 years, but eventually a number of infected animals will develop clinical disease. This means that they start to rapidly lose condition, and usually die within the next 3 - 6 months.
There is no cure for the disease. Infected animals, and especially clinical cases, shed large number of Johne's bacteria in their dung, which then contaminate pasture and water and pass the infection on to other stock.
The building blocks for disease risk management
The strategies to prevent the disease entering your flock, and to minimise the impact of the disease if your flock is already infected, can be divided into two categories.
1. Reduce the risk of the disease entering your flock by:
- Only purchasing low risk sheep
- Only purchase rams from assured vaccinating studs
- Only purchase replacements which were vaccinated as lambs
- Only purchase replacements from lower risk flocks. e.g.: assured flocks
- Request a completed Sheep Health Declaration from the vendor
- Vaccinate any non-vaccinated replacements on arrival
- Follow the same rules if bringing in agistment stock
- Avoiding sheep straying on and off your property
- Maintain fences to prevent sheep straying on and off your property
- Encourage neighbours to vaccinate
- Start a vaccination program in your own flock.
2. If already infected, reduce the level of infection in your sheep by:
- Vaccinate all replacement lambs at marking
- Test to monitor level of infection
- Consider vaccinating any older sheep which have not had high exposure to contaminated pastures
- Optimise natural immunity by:
- Ensuring adequate ewe and lamb nutrition
- Ensuring good weaner nutrition and growth
- An effective worm control program.
- Prepare 'low risk' lambing and weaning paddocks. Six weeks destocking has been shown to dramatically reduce contamination levels particularly over summer
- Graze young sheep separately from older sheep
- Cull any test-positive or 'high risk' mobs from your flock
- Dispose of sheep with clinical signs of OJD as soon as possible
- Fence off wet areas and avoid grazing these with young sheep
- Reticulate water from a clean source (eg bore water) to avoid sheep watering out of contaminated dams
- Avoid feeding supplements on the ground
- Only purchase in, or agist, low risk (vaccinated) replacements
- Minimise sheep straying by maintaining boundary fences
- Encourage neighbours to vaccinate
- Progressively destock and decontaminate sections of land.
The importance of vaccination
The vaccine trials currently indicate that vaccine:
- Reduces deaths by 90%
- Reduces shedding of the OJD bacteria by 90%Vaccination is the best strategy for producers with infected flocks. This means vaccinating all replacement lambs at lamb marking or weaning. This should be the backbone of any management plan.
- It is also worth vaccinating any hoggets or adult sheep which have not been heavily exposed to the Johne's bacteria.
- Overseas experience suggests that it is also very important to adopt additional strategies that reduce exposure to susceptible lambs and weaners. That way you give the vaccine the best chance of working effectively in your flock.
For further information:
Animal Health Australia - ojd.com.au