By Dr Charlie Blackwood

What is Johnes Disease?

Bovine Johnes Disease (BJD) is a disease caused by the bacteria Mycoplasma paratuberculosis. BJD is contracted by animals less than 1 year of age. Calves are most susceptible soon after birth, and gradually develop resistance to the disease as they become older. Calves infected with BJD rarely show any signs of disease until they are 4-8 years old, although they may shed bacteria in their poo (which can infect other animals) before this time. Once the bacteria enter the body, they target the cells of the gut to decrease food absorption. As BJD stops your cows from absorbing food, cows with clinical disease will lose weight and have diarrhoea. Some may also have a swelling below their jaw known as ‘bottle jaw’.

Why control it?

  • BJD causes decreased production in your herd. An infected dairy cow will produce 8.25% less milk than if they were uninfected and studies indicate that presence of BJD in the average Victorian dairy herd will cost $2370 each year in decreased production. Milk quality is also reduced, and infected cows tend to have milk with lower fat and protein than milk of unaffected cows.
  • Cows with BJD are more likely to get other diseases (e.g. mastitis). These cows will often need veterinary attention, and may be prematurely culled either due to signs of BJD or another disease process.
  • As animals with BJD present with clinical signs similar to a number of other disease processes, money is often spent treating these animals for more common diseases (e.g. drenching for parasites) prior to correct diagnosis.
  • Property values can also be decreased by the presence of BJD on a property.
  • There is some evidence that Johnes disease in cattle is linked to Crohn’s disease in humans. If this is the case it is important that infected animals and animal products are not allowed to enter the human food chain.

How do I know if my cows have it?

We can test for BJD by faecal culture or by taking a blood test. Generally a blood test is the easier and cheaper way of testing for disease. The blood test used is very specific therefore it is very unlikely that uninfected cows will test positive. However as the test looks for antibodies to the disease, young infected animals which have not yet begun to fight the disease will not be detected. For this reason when doing routine testing for BJD we usually only test animals that are greater than 4 years old who are more likely to have antibodies to the disease. Occasionally we see animals less than 4 years old with clinical signs of the disease and these will be tested.
Note: legally farmers and vets have to report suspected cases of Johnes Disease.

How can I control it?

To control BJD management plans need to focus on preventing infection of animals in the first year of life. Although we can’t prevent the bacteria from infecting a calf across the uterus before birth, we can stop calves from drinking BJD infected milk or having access to manure from adult cattle. The Johnes Disease Calf Accreditation Program (JDCAP) is a program which aims to reduce the incidence of disease and allows farms to receive accreditation as being low risk BJD properties.

Some guidelines in raising calves to decrease risk of BJD are as follows:

  • Calve animals in a clean dry area with minimal faecal contamination
  • Remove calves from their mother within 12 hours of birth
  • Ensure that calves receive colostrum within the first 24 hours
  • Make sure that calf areas (and equipment used for calves) are free of manure from adult cattle.
  • Make sure that calf paddocks have not been grazed by adult cattle in the previous year
  • Only purchase animals from farms which follow similar or more comprehensive BJD management.

If any cattle are showing signs of BJD notify a vet. If the disease is present, spread and impact of the disease can be reduced through early action. Because infected animals can take years to show symptoms of BJD and infected animals can be purchased onto a property infecting your herd, we recommend that all dairy farms manage their calves according to the above guidelines therefore reducing chance of spreading BJD.

Conclusions

BJD is a disease with significant herd health, environmental and economic impacts for the dairy or beef producer. Although the consequences of the disease can be severe, good farm management means that this disease can be diagnosed and controlled to decrease the impact of disease on your farm. There are a variety of programs available which in conjunction with veterinary advice can give a framework through which BJD can be controlled and eliminated from your herd.

Summary of changes on the management of JD in Victoria

There has been a marked change in the approach to the management of Johnes Disease in cattle which came into effect from the 1st July 2016. The general thought behind the changes in Johnes Disease are:

  • From 1st July 2016, Johne’s disease in cattle will be industry managed and market-driven in Victoria.
  • Management of Johne’s disease in cattle will be on a risk-based approach at the farm level, the same as for many other endemic livestock diseases.
  • With a strong emphasis on good biosecurity practices, this approach will put the management of Johne’s disease in the hands of the cattle owner.

Following are the main changes that will occur from 1 July 2016:

  • The department will no longer apply or record a Johne’s disease herd ‘status’ (e.g. Infected or Suspect) for cattle herds in Victoria.
  • Johne’s disease herd statuses previously applied by the department will no longer be recognised (excluding CattleMAP).
  • Johne’s disease will continue to be notifiable in Victoria. Although a suspicion or diagnosis of Johne’s disease in cattle will to need to be notified to the department, no further regulation will be applied to herds for which a notification is received.
  • The voluntary TCP for infected cattle herds will conclude on 30 June 2016 and be replaced by an industry funded subsidy for Johne’s disease vaccine from 1 July 2016 to 31 December 2019.
  • Industry subsidisation of participation in the Johne’s Disease Calf Accreditation Program (JDCAP) will also continue to 31 December 2019.
  • Cattle from interstate properties infected with Johne’s disease will be permitted entry into Victoria without the need to obtain a permit from the department.
  • Although national zones for Johne’s disease in cattle will no longer exist, states/territories may impose entry requirements in relation to Johne’s disease.
  • The change in approach follows a national review in 2015 of bovine Johne’s disease management that industry and governments contributed to through an extensive consultative process. The review identified there was support for Johne’s disease in cattle to be addressed under a common biosecurity approach for endemic diseases,with a focus on management at the farm-level.

Further details on the future management of JD in Victoria, can be found on the Agriculture Victoria BJD webpage. Since vaccination will be subsidised in some situations, farmers may consider vaccination with the Johnes vaccine. Farmers should discuss the pros and cons of vaccination with their veterinarian.

For more information on Johnes Disease in cattle, the JDCAP calf rearing program and Johnes Disease vaccination, talk to one of our cattle vets.