Understanding Johne's Disease in cattle
Johne's disease is a chronic wasting disease of cattle. It is caused by infection with a bacteria Mycobacterium avium subspecies paratuberculosis (MAP). Johne's Disease is a welfare and economic concern to farmers as it doesn't just cause disease and death in cattle but also results in production losses.
The challenge of Johne’s
A key challenge with Johne’s is that clinical signs take a long time to develop and "silently infected" cows can spread the infection before they begin to show obvious signs of clinical disease (diarrhoea and weight loss) at two to five years of age or more. As the disease is often not detected until years after the initial infection, some farmers call it a ‘ticking timebomb’. It is important not to wait for symptoms to appear because, in the meantime, the herd is likely to be less productive.
While cattle remain susceptible to infection throughout their life, they are at their most vulnerable in the first few months of life. There is currently no cure currently for Johne’s, but there are steps farmers can take to reduce the risk in their herd. Early detection and, if resources allow, the segregation of infected animals as early as possible, whilst taking management steps on the farm to reduce the spread of infection, for example, not breeding from animals or their offspring which have tested positive are the keys to control.
Testing for Johne’s
The aim of testing is to identify infected animals in the herd as soon as possible so that management decisions may be taken to prevent the spread of infection from infected cows to the rest of the herd. When infected animals start shedding the MAP bacteria in their faeces, they become 'infectious'. However, this shedding can be intermittent and can actually occur before antibodies can be detected by the test adding to the challenge of the disease.
The main test used to diagnose Johne's disease is a blood test to look for the antibodies that the animal has produced in response to infection with the bacterium that causes Johne's disease. Blood testing is the most suitable sample format for beef suckler herds. A blood test can detect Johne’s infected animals which look perfectly healthy earlier than faecal tests are able to. This allows identification of infected animals as early in the course of infection as possible.
Dung sampling helps to determine whether an animal is shedding bacteria and is infectious to others, helping with decision making on whether to cull positive animals. It is important to consider that a blood positive animal may have a clear dung test, which doesn’t mean the animal is not infected, they may not be currently shedding but have the potential to shed in the near future.
In addition, the tuberculin skin test for TB can interfere with the blood test for Johne's disease. Current guidelines state that blood testing for Johne's disease should not be performed within a minimum of three months after a cow has received a tuberculin skin test.
Accreditation and health schemes
The Johne’s Disease Risk Level Accreditation programme (the standards set by CHeCS) enables herds to maintain or move towards clear herd tests (for breeders) and provides assurance that an effective test and control programme is in place (for buyers). Find out more information regarding SRUC Veterinary Services Premium Cattle Health Scheme (PCHS).
It can take time, but by following the CHeCS guidance, farmers can lower the level of disease and will reduce the risk of it spreading now and to future generations in their herd.
Johne’s Disease survey
SRUC is currently working on Johne’s Disease as part of a larger biosecurity research project funded by the Scottish Government.
A survey has been designed to build a better understanding of the management practices that help prevent infection, as well as the factors that may make herds more vulnerable to the disease.
The survey is primarily aimed at beef producers, although dairy farmers are also encouraged to take part. The survey can be completed on a phone, tablet or computer, with most responses collected through simple drop-down menus. A paper copy is also available on request.
Take part: app.onlinesurveys.jisc.ac.uk/s/sruc/survey-about-johnes-disease-2026
Kate Lamont, Senior Lecturer, Kate.Lamont@sruc.ac.uk
Posted by SAC Consulting on 21/07/2026
