Avoiding OJD – Fact Sheet

All sheep and goat producers need to be aware of the risk management measures available to avoid infection of flocks and help control the spread of OJD.

Different farm enterprises will require different techniques and it is ultimately up to individuals how to manage their flocks.

Following is some basic information about the disease and ways in which you can minimise the risk of introducing it into your flock. Also see the links to other sites.

OJD is a chronic gut infection in sheep caused by the bacteria Mycobacterium paratuberculosis. Infected sheep, especially ones in which the disease is well advanced, shed very high numbers of bacteria in their manure. Other sheep become infected by grazing on pasture contaminated by infected sheep manure. Young sheep are particularly susceptible.

It is predominantly a disease of sheep although other species may occasionally become infected. There is no evidence of OJD being transmitted to sheep by cattle or wildlife. OJD has a very long incubation period and, during much of this time of subclinical infection, sheep can be steadily shedding more and more bacteria. Obvious signs of disease are usually only seen in adults. A proportion of infected sheep will develop wasting, and possibly scours, which generally results in death 1-3 months later. As the infection becomes more established in a flock and bacterial contamination increases on the ground, the number of obviously affected sheep generally increases slowly. But these are still only the tip of the iceberg.

In some infected flocks, mortalities can increase to unsustainable levels over time, despite good flock management.

The highest risk of OJD infections however comes from introduced infected sheep, including agisted sheep. Most infected sheep are in the subclinical stage of infection and show no obvious signs of having the disease; but they can still spread the disease. However OJD may also enter a property from infected neighbouring properties through straying sheep or washing of dung across boundaries so maintaining stock proof fences and other barriers is important.

The Assurance Based Credit Scheme (ABC Scheme) was launched in 2004 as a national standard for assessing and assuring flocks for OJD. A consignment of sheep can have a score between 0 and 10. The higher the score, the better the assurance.

To reduce the risk of introducing infected sheep, a producer should firstly know his or her own flock’s ABC score and only buy sheep where the vendor has provided a completed National Sheep Health statement (which can be found in the toolkit on www.farmbiosecurity.com.au) that declares a score that is at least equal to but preferably higher than their own flock.

See the SheepMAP section for a list of assessed flocks.

Page Updated: 9 September 2010