Johne's disease: how to spot and report the disease

Detecting Johne's disease

Because it takes a long time for signs of Johne's disease to appear in infected cattle, you may not know that it is present in your dairy herd. It is very important to look out for signs of the disease and it is advisable to take steps to screen the herd for the presence of Map. This will help you and your veterinary surgeon understand the risk in your herd, and decide the best course of action, particularly in preparing a herd health and welfare plan.

Once disease is established in an animal and it is symptomatic (for example it has severe diarrhoea and is losing weight) the disease can normally be readily confirmed by a blood test or by PCR testing of dung.

However, diagnosis of the presence of the organism in animals in the silent period of the infection, before signs become apparent, is difficult. Infected cattle seldom pass detectable numbers of Map in their dung until they are beyond two years of age.

There is a blood test that detects the antibody to Map produced by infected cattle. However, cattle tend to produce the antibody to Map relatively late in the infection. In some individuals it may be difficult to confirm the presence of infection in the live animal. Where an infected animal is tested throughout its life it can be expected to test negative on one or more occasions before it tests positive. This also means that testing apparently healthy animals at the point of sale or on arrival in their new herd cannot guarantee prevention of the introduction of infected animals to the herd.

Taking these realities into account, you should consult your veterinary surgeon to develop a screening programme that best suits your business needs. For example:

• if you believe your herd is not infected and you wish to provide a high level of assurance for certification to support sales, a regular testing programme may be appropriate- this might take the form of a blood test every one or two years on all or part of the adult herd, combined with tests on any "suspect" animals or other culls
• if you believe your herd is not infected but wish to ensure its early detection if disease does occur, then tests on suspect cases, on culled cows, or periodic screening of a proportion of the older animals in the herd may be useful to support this position
• if you know Johne's disease is present in your herd and want to try to eradicate it, a more intensive programme will be needed in conjunction with other management controls - you may wish to consider getting involved with schemes such as Cattle Health Certification Standards (CHeCS) or The National Johne’s Management Plan through Action Johne’s