Managing the risk of ovine Johne's disease

Page last updated: Monday, 20 November 2017 - 11:23am

Please note: This content may be out of date and is currently under review.

Ovine Johne's disease (OJD) is a chronic, incurable, intestinal disease that affects sheep and sometimes goats and deer. It causes weight loss and death in older sheep. OJD is mainly spread by the movement of sheep which appear normal but are infected with the causative bacteria. Infected sheep will shed the bacteria in their faeces long before they appear unwell. Water movement and stray sheep also present a risk.

Reducing the risk of OJD entering your flock

A closed flock with good boundary fencing are the best defences against OJD. If you do buy sheep, maintain good biosecurity practices. Biosecurity measures taken to keep out OJD will also reduce the risk of other diseases such as footrot and lice.

The biggest risk of introducing infection to your flock is through the introduction of sheep: purchased, agisted or straying. Infected sheep can shed the bacteria in their faeces for years before the disease becomes apparent.

The disease can also spread through infected faeces in surface water, including paddock run-off after rain and through contaminated faeces on equipment and sheep trucks.

What is my risk?

These factors increase the risk of OJD entering and establishing in your flock:

  • buying in or agisting sheep
  • trading sheep which remain on the property beyond two years of age
  • running a mainly sheep enterprise with permanent pastures and a high stocking density
  • being in a higher rainfall zone (400 millimetres or more per year)
  • having an infected neighbour
  • being on a common water catchment
  • high numbers of stray sheep on your property.

Low-risk sheep and genetics

If you do introduce sheep, aim to introduce them only from flocks with the same or better health status than your own.

  • Use the national sheep health statement (SHS) to help you achieve this.
  • Buy from SheepMAP accredited flocks — the higher the monitored negative (MN) status, the greater the level of assurance that the sheep are OJD-free.
  • Buy from flocks with a recent testing history — either pooled faecal culture testing or abattoir surveillance.
  • Buy from closed flocks. In the absence of testing, the fewer sources a flock has introduced sheep from, the lower the risk that they have brought in OJD.
  • Buy sheep that have approved vaccinate status. Vaccination does not provide a guarantee that an animal is not infected but it does greatly reduce the risk. Approved vaccinates will carry an ear tag with a 'V' in a circle on them.
  • Check the status of properties before you send sheep away on agistment.
  • Introducing genetics as semen or embryos reduces the risk of introducing disease.

These factors are all covered in the national sheep health statement (SHS). Always ask for an SHS when buying or agisting sheep.

Boundary fences and stray sheep

  • Check for strays regularly, remove and isolate any that you find.
  • Maintain fences to prevent straying.
  • Work together with neighbours to reduce the risk of sheep straying.

Vaccination

Vaccination alone does not stop a flock from getting OJD but it does significantly reduce the chances of infection and reduces the shedding of bacteria in the faeces if sheep do become infected.

Vaccination against OJD is a valuable tool in reducing rates of both infection and clinical disease in infected flocks. It can also be a valuable tool in uninfected flocks to give better protection against infection and to provide market benefits (for example, if you sell breeder sheep).

Other biosecurity measures

  • Restrict visitor and vehicle movements onto your property to designated driveways and access roads.
  • Only transport sheep in clean vehicles. Discuss vehicle cleaning protocols with your transporter.
  • Check the health protocols for shows and breeding centres and isolate sheep as much as possible.
  • Maintain good animal movement records to ensure whole-of-life traceability.
  • Inspect your sheep regularly, especially recent introductions, and report any unusual signs to your veterinarian.
  • Seek advice from a veterinarian or farm consultant to develop and implement an OJD risk minimisation strategy for your farm.

Factors that reduce the risk of OJD entering your flock:

  • running a closed flock
  • maintaining good biosecurity practices
  • buying only vaccinated animals or those from flocks with a testing history
  • using the SHS when buying any sheep
  • fencing off common waterways and dams with run off from neighbouring properties
  • promptly removing any strays and managing high-risk paddocks.

If OJD enters your property, these factors reduce the risk of it establishing and causing severe disease in your flock:

  • low rainfall zone (below 400mm per annum)
  • sheep/cropping enterprise with the emphasis on cropping
  • maintaining a young flock
  • introduced sheep leave the property before they are 12 months old.

Contact information

Anna Erickson
+61 (0)8 9881 0211