About OJD

General information on Ovine Johne's Disease (OJD)

Since it was first found in Australia in 1980, Ovine Johne's Disease (OJD) has proven to be a costly disease. It spreads slowly, is difficult to detect early on, causes lowered weight gain and wool production and can kill about 10% of adult sheep each year if left unmanaged.

What is the disease?

OJD is a wasting disease caused by the sheep strain of the bacterium, Mycobacterium paratuberculosis, which grows mainly in the small intestine.
The intestine wall slowly thickens and the animal has increasing trouble absorbing nutrition from its food. Infected animals slowly lose condition and usually die within 3 to 6 months of showing signs.
Scouring may occur, but is not seen routinely.
Merinos are more susceptible than crossbreds and British Breed sheep.
Goats and cattle can be infected but infection is rare. Alpacas may be infected by OJD.
There is no cure for OJD.

How does it spread on farm?

The OJD bacteria are shed in huge numbers in faeces.
Animals pick up the infection from contaminated teats, pastures and water.
The bacteria can survive many months in shaded environments.
Sheep are most commonly infected as weaners, with deaths often showing up in the two and three year olds.
Lambs can be infected before birth.

How does it spread between farms?

Bought sheep and strays are the main risk.
Sheep droppings and contaminated run-off can also spread the infection between farms.

Why bother about OJD?

In Australia, annual death rates around 10% are common if OJD is not managed.
Recent New Zealand research shows losses of 17% of weaner weight and 10% of wool cut in sub-clinical cases in crossbred sheep.
Once it gets into an area all flocks are at risk. The earlier you act, the less the impact of OJD on your business and other flocks in your district.
Assuring sheep buyers about the OJD status of your sheep is becoming the norm.

How do I know if my sheep have it?

There is often no sign for the first few years.
Some animals can be infected and spreading the disease but the flock can still look fine.
The first thing you might notice is a persistent tail in one or two mobs that won't respond to drenching.
You might notice a few poor doers that aren't around next time you check in the paddock.
By the time you see obvious OJD deaths the disease is likely to be well established and it will take some years to get the situation under control.

What can I do to keep the disease out?

This depends to some extent on whether your flock is already infected and how much OJD is in your district, but there are some basic rules:
Only buy in vaccinated sheep or sheep that are low risk according to the accompanying Sheep Health Declaration.
Vaccinate your flock if there is a risk of OJD coming in with purchases or from neighbours.
Improve your flock's resistance to disease through good nutrition and worm control.
Work with neighbours to reduce spread between farms.

What can I do if my flock is already infected?

Vaccinate all animals as lambs (before 16 weeks of age).
Cull all sheep showing signs.
Use the dung test (pooled faecal culture-PFC) to identify and cull heavily shedding mobs.
Manage your grazing patterns to reduce exposure of young sheep to OJD.
Clean up contaminated pasture by:
Avoid feeding on ground - go for troughs or automatic feeders.
Consider changing your enterprise mix so that you are running fewer susceptible animals.