Johne’s disease (JD) in sheep (sometimes called ovine Johne’s disease (OJD)) is often not diagnosed in a flock until a significant proportion of the flock is already infected and deaths are occurring. There is often no sign for the first few years, which is why OJD may be referred to as a ‘silent but costly disease’.
Infected sheep can be shedding the bacteria in their manure for a considerable period (sometimes years) even though the flock still looks healthy, but they are contaminating the pasture and infecting other sheep.
The first sign of the disease in a mob is usually a distinct ‘tail’, with sheep ranging in condition from good to very poor, then the sheep in the ‘tail’ start dying. The number of sheep in this classic ‘tail’ may be constant, but it’s comprised of different animals over time, eroding flock numbers and profits.
JD-infected sheep continue to eat and drink normally until they are too weak to graze, and eventually die. Scouring may occur, but is not a common feature of JD in sheep. In some large flocks, the number of deaths may only be appreciated when big discrepancies occur in counts of adult sheep.
When obvious JD deaths are noticed, the disease is likely to be well established. It will take the producer some years to get the situation under control, during which time deaths will continue. The best place to look for the disease is in 2 and 3-year olds, but sheep from weaners through to older adults can also die from the disease.
2018 Review of the National JD Management Plan
Management of Johne’s disease in sheep in Australia beyond 2018 will continue as part of the Sheep Health Project at Animal Health Australia, enabling producers to still be able to use all the on-farm practices and tools currently recommended as part of a best practice approach to control.
The previous five-year National OJDMP (which ended in June 2018) is not being extended. The decision has been made by the sheep industry’s peak industry councils – Sheep Producers Australia and WoolProducers Australia – based on expert technical advice that producers can continue to effectively manage the endemic disease as part of their overall approach to animal health and biosecurity.
National Standard Definitions, Rules and Guidelines (SDR&Gs)
The standard definitions and rules for ovine Johne’s disease are the agreed national standards for the disease management program.
First endorsed in 1998, an interim version for OJD in sheep and goats was released in 2013; the final version will be available when PCR implementation guidelines have been developed.