Bovine Johne's Disease

Causes:

BJD is caused by the bacterium Mycobacterium avium subsp. paratuberculosis.

The bacteria live in the animal's intestines and cause thickening of the bowel wall which prevents normal absorption of nutrients. Calves can become infected when drinking from an udder contaminated with manure, or eat or drink feed or water contaminated by manure. Calves can also be infected by cross-suckling, or by picking up infection from contaminated ground.

Because of the risk of infection — before as well as after birth — all calves born to infected cows are highly likely to be infected.

Milk from infected cows is also considered a risk.

Conditions when likely to occur:

The prevalence of Johne's disease varies in different regions of Australia. It is most commonly found in the south, and particularly in dairy cattle herds in high rainfall areas. It can also occur in beef cattle.

More information on prevalence zones and the BJD national strategic plan can be found on the Animal Health Australia website.

Clinical signs: Diarrhoea, progressive weight loss despite a good appetite, emaciation in older animals, bottle jaw, chronic ill thrift, fall in milk yield, and eventually death

Treatment:

There is no treatment for JD and animals showing clinical signs inevitably die.

The laboratory tests for JD are unreliable or take a long time to complete; therefore, eradication of the disease is difficult. Leaving properties or paddocks empty of stock for a period of time can eliminate the bacteria from the environment. The period of time will depend on environmental conditions.

A National Johne's Disease Control Program (NJDCP) has been in place in Australia since 1996.

Management strategy to prevent disease:

-        Developing and implementing a farm biosecurity plan.

-        Only purchasing animals with an animal health statement and only introducing low-risk stock onto the property.

-        Implementing grazing management strategies to prevent the spread of the bacteria on-farm.

-        Weaning early to limit infection of young calves, lambs and kids.

-        Vaccinating sheep.

Strategies for managing bovine Johne’s disease (BJD):

Eradication versus living with BJD

• Cost benefit of eradication (and feasibility). This should only be considered in consultation with your veterinary consultant and financial advisor.
• If living with the disease, structure stock sales to minimise ongoing impact of disease. For example, try to target stock for slaughter rather than store sales. Run a young herd and if mortalities are an issue consider a test and cull program. Plan a property management program in conjunction with your veterinarian. Financial assistance may be available for eradication.

Risk assessment protocol:

• Purchase cattle from low-risk zones: Free and Protected (maps for these available on websites from state departments of agriculture and Animal Health Australia)
• In Control and Residual Zones, BJD is common in dairy herds but very uncommon in beef herds that have had little or no contact with dairy cattle. Assess risk more carefully when introducing cattle.
• Observe regulations with regards to the movement of cattle between BJD zones and states.
• Market Assurance Program (CattleMAP) – highest level QA program for BJD assurance. MN3 is highest assurance>MN2>MN1. Details of MAP herds on Animal Health Australia website
• Check Test – In non-MAP herds with no suspicion of infection, it is possible to undertake a low level assurance test on selected adult animals in the herd aimed at increasing the probability of detecting infection. The Check Test requires 50 adults to be tested or all adults over two years if less than 50 in herd. The Check Test is valid for 12 months valid in and only used to support a Vendor Declaration of animals bred in that herd or to animals introduced with a vendor declaration as originating from Check Tested or higher status herd. Additional testing procedures including Testing to MAP Standard (TMS) and Tested 4 year olds (T4YO) are sometimes use for cattle to gain entry to MN1 herds.
• Beef Only - Beef Only is a herd category to help assure cattle buyers about the very low risk of BJD in beef herds that have had no contact with dairy cattle. The beef cattle industry and state animal health authorities agreed in September 2004 that cattle from herds that qualify as Beef Only represent a low risk of BJD. They also agreed that herds that qualify as Beef Only can trade into BJD Protected Zones of New South Wales, Queensland and South Australia without herds having to be tested. Audits of written declarations at saleyards have found high levels of compliance with the scheme. Herds classified as infected, suspect or restricted for BJD are not eligible. Eligible herds must have not grazed with dairy and dairy cross cattle for five years unless those herds were enrolled in the CattleMAP or grazed on land that has grazed dairy or dairy cross cattle over two years of age within the previous 12 months unless they are from herds that are enrolled in the CattleMAP. Only introduce cattle from a herd with the same or higher BJD status and introduce cattle with an approved animal health statement issued by the owner/person in charge of the animals. Click here for more information.
• On-farm quarantine: Not practical given long time delay for development of disease and low sensitivity of tests in individual cattle. Only introduce cattle to property if they are at a similar or higher status.