There is no one solution when it comes to managing JD. Each property manager should develop a flock disease control program which takes into account the current disease status of the flock and the risks to which the flock is likely to be exposed.
An effective disease control program for JD uses a range of tools and strategies both to keep JD off a property and to manage the infection once it has occurred. Fortunately, there are a number of tools available to sheep producers to assist in managing the risk of JD. However, the first step in the management and control of JD is to assess the animal health risk of sheep and to avoid buying in high-risk animals. Additional farm biosecurity activity, such as maintenance of fence lines and isolation of straying stock supported by the use of vaccine and grazing management, will help protect the flock and create pastures with low levels of bacterial contamination.
Why Manage JD?
JD infection can result in significant economic losses on infected farms due to sheep deaths, lost production and trading restrictions. Owners of flocks that are infected with JD who undertake no appropriate management measures will, over time, experience heavy production losses and deaths as the level of infection within the flock increases. Annual death rates in infected Australian sheep flocks of up to 25% annually have been seen in the past and in a self-replacing flock lambing percentages can fall to an unsustainable level.
What to do if you have JD?
Assessing your risk
Understanding your flock’s risk of exposure to JD is the basis for developing the management and control programs you put in place. The first step is to recognise that JD is most likely to be introduced with infected sheep, either at time of purchase or through agistment. In regions where the disease is well established ‘lateral spread’ can also occur along waterways and through fencelines.
How much risk of infection you flock has and will be exposed to will depend on a range of factors including:
- Sheep movement and purchase decisions you have made in the past
- What testing has occurred in flocks from which you have purchased
- The trading history of the flocks you have purchased from
- The geographic area where your farm is situated
- Whether your neighbours have JD
- What testing you have undertaken and your attention to farm biosecurity practices
- Your flock’s vaccination status
- The location from which the sheep are sourced and whether the sheep are homebred or from a trader’s flock
- Grazing management strategies you have in place to minimise pasture contamination
Using a Sheep Health Declaration is a practical way of obtaining much of the information outlined above for sheep that you bring onto your property.
Watch your flock closely and investigate any sheep that are losing condition.
Vaccination
A vaccine against JD called Gudair® is registered for use in sheep in Australia. This vaccine is a valuable management tool to help control the spread of the disease but is not a “silver bullet” . The vaccine does not prevent infection entirely, however it does significantly reduce the number of sheep that die from JD and in most flocks, decreases the amount of bacteria passed in the dung. This reduces environmental contamination and provides less opportunity for disease transmission.
It is important to remember that vaccination is not 100 per cent effective. Some vaccinated sheep may develop ‘subclinical’ JD infection and shed bacteria in their dung without showing obvious signs of illness. Some vaccinated sheep will eventually develop severe ‘clinical’ JD and may shed very large quantities of bacteria on the pasture before they die. Any sheep showing signs of wasting should be immediately culled to reduce pasture contamination.
Effective prevention and control of JD requires a multi-pronged approach of vaccination, abattoir monitoring/testing, purchasing and selling sheep with high assurance declared on the national Sheep Health Declaration.
Using the Vaccine
The Gudair® vaccine can be administered to sheep from four weeks of age. It is an inactivated (killed) vaccine so there is no risk that vaccination will introduce JD into uninfected flocks. A single 1mL dose is given, most commonly at lamb marking. It is recommended that lambs are vaccinated before 16 weeks of age. Booster doses are not required.
Injection site reactions are common with Gudair® and it is important to administer the dose under the skin high on the neck behind the ear. Animals should be adequately restrained during vaccination. Young lambs should be vaccinated in a lamb marking cradle. Weaners, hoggets and adult sheep should be packed tight in a race and have their heads held high to ensure the vaccine is delivered at the correct site. Vaccinated sheep must be identified with a NLIS (sheep) tag that contains the property identification code or number and the letter ‘V’.
More information is available on the Zoetis website. This includes advice on safe use of the vaccine.
Note – Producers and veterinarians should be aware that accidental self-injection with the JD vaccine, Gudair® can cause a severe and persistent reaction. Vaccinators should be trained in correct vaccination technique and safe handling of vaccinating equipment. For further information contact your animal health advisor or Zoetis on 1800 ZOETIS – 1800 963 847.
Grazing management
Prolonged exposure to JD-contaminated pastures appears to be a major factor leading to high infection rates within flocks. The primary aim of using grazing management as a strategy to manage JD is to reduce the exposure of lambs to Mycobacterium paratuberculosis both before and after weaning. Ideally grazing management should be combined with an JD vaccination program.
It is difficult to avoid exposure of lambs to some level of JD contamination before weaning if they are born into an infected flock. The main source of contamination will be infected ewes and the pastures they graze. Exposure can be reduced by lambing onto specially prepared ‘low contamination’ pastures and by early weaning to separate lambs from infected ewes. It is also important to immediately cull any ewe showing signs of wasting, as these sheep may shed large numbers of JD bacteria.
Low-contamination pastures can be prepared for lambing ewes and/or weaners in 6–12 weeks during summer and six months in other seasons by:
- grazing with steers
- rotating with crops
- re-sowing pasture
- grazing with terminal lambs and selling them straight to slaughter
If low-contamination pastures are scarce, then preference should be given to the weaners rather than lambing ewes. Hoggets and ewes are susceptible to infection, but sheep exposed as adults are less likely to develop clinical disease than those exposed as young sheep and lambs.
More information is available on the Meat & Livestock Australia fact sheet titled ‘The role of grazing management in the control of Johne’s disease’
Farm biosecurity
Implementing a simple biosecurity plan will help to prevent JD and other major production limiting diseases (as well as pests and weeds) from entering your farm. Introduced and straying sheep present the greatest risk of JD introduction to your farm therefore purchasing sheep that have the lowest risk must be a primary aim when buying sheep. Ideally, introduced sheep should come from flocks at low risk of JD or for extra assurance from Market Assurance Program (MAP) accredited flocks. Producers should always ask questions about the sheep they intend to purchase and should request a signed Sheep Health Declaration.
Remember biosecurity is not hard;
- Know your own flock’s disease status
- Identify the likely sources of disease
- Develop an animal health plan to minimise these risks
- Continue to monitor for the absence of disease
- Ensuring that your boundary fences are secure and in good order will help prevent neighbour sheep straying onto your property is an easy first step.
Further information on farm biosecurity is available on the Farm Biosecurity website.
Abattoir monitoring
Abattoir monitoring is a practical and cost effective means of checking for JD. Trained inspectors at abattoirs inspect lines of adult sheep (2 years or more) for visible signs of JD in the intestines and lymph nodes.
Abattoir monitoring aims to identify infected flocks – this is particularly important for areas with little or no known prevalence. Abattoir monitoring also provides feedback to producers on the effectiveness of their JD management programs and producers with negative monitoring results, may be eligible to trade their sheep as having a lower risk of being infected with JD.
There are two abattoir monitoring negative status results that producers may use:
- Abattoir 500 status – where at least 500 sheep, over 2 years of age, have been submitted to an abattoir in the past 24 months, in 1 or more lots, and have been examined and all found negative for JD. The sheep must have been on the property for at least 2 years.
- Abattoir 150 status – where at least 150 sheep, over 2 years of age, have been submitted to an abattoir in the past 12 months, in 1 or more lots, and have been examined and all found negative for JD. The sheep must have been on the property for at least 2 years.
To obtain information about your abattoir monitoring results or to request inspection to be arranged at your abattoir, please contact your State JD coordinator or the abattoir directly.
Inspecting for JD in the abattoirs
Sheep that are infected with JD may show the following changes in their intestines:
- a thickened gut wall, particularly the ileum and ileocaecal valve,
- prominent mesenteric lymphatic vessels, and
- enlarged, pale lymph nodes.
If the sheep have lesions suggestive of JD, the inspector collects samples from up to three sheep in a line. These samples are submitted to a laboratory for microscopic examination.
The pathologist at the laboratory looks for the presence of cellular changes and bacteria that are consistent with infection by Mycobacterium paratuberculosis. If no typical cellular changes are present and bacteria are not found the result will be negative. The presence of both lesions and bacteria will result in a positive result. The presence of typical cellular change where no bacteria are found will result in an inconclusive result.
Image of M paratuberculosis in cells of the intestinal wall Courtesy University of Wisconsin