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 Statement.
  • 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:
      • grazing with adult cattle,
      • rotating with crops,
      • re-sowing pasture,
      • grazing with 'clean' sheep, then selling them straight to slaughter
  • Avoid feeding on ground - go for troughs or automatic feeders.
  • Consider changing your enterprise mix so that you are running fewer susceptible animals.

What happens if I do nothing?

  • If your flock is already infected and you do nothing:
      • The disease will slowly spread throughout your flock.
      • Each new drop of lambs will be exposed, and eventually a significant proportion of your animals will be infected.
      • You may see mortalities early on, or they may not start until your animals are older or under stress, eg when feed gets tight or worms get going.
      • There is a strong chance that your sheep will spread the infection to neighbours.
  • If your flock is not infected and you do nothing:
      • You run the risk of eventually ending up with infection.

For further information, contact:

  • Local vet
  • Tasmanian Sheep Market Assurance Program vets
  • DPIPWE Animal Health staff: call 1300 368 550
  • The Tasmanian Farmers and Graziers Association
  • Your stock agent

Further information

Animal Health Australia


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