A promising new test for Johne’s disease in dairy cattle has been developed at the Institute for Global Food Security (IGFS) and School of Biological Sciences at Queen’s University Belfast.
In terms of animal health, JD (and CAE) is a significant concern and a major production-limiting disease of farmed goats world-wide.
Estimates from other industries collated from farmer surveys suggest that JD is common and widespread in NZ: 60% of deer herds, 68% of sheep flocks, 31% of beef herds and 60% of dairy cow herds harbour some Johne’s infection.
Recently we asked Dr Rory O’Brien, an expert on the control of JD and the research manager of DRL’s Dunedin testing service, to explain JD and its impact on New Zealand dairy goats.
What is Johne’s disease?
Sometimes called paratuberculosis, Johne’s disease is a bacterial infection that leads to inflammation and thickening of the intestines. This results in problems which can include reduced uptake of nutrients, progressive weight loss and death.
The bacterium which causes JD is called Mycobacterium avium paratuberculosis, also called MAP for short.
Often described as an iceberg disease (for every clinically affected animal showing symptoms of disease, many more will be lurking beneath the surface) JD is chronic, progressive, contagious and widespread.
How does JD present in dairy goats?
Goats are notably less likely to visibly scour (have diarrhoea) from JD than other species which means this is an unreliable diagnostic indicator of disease.
More often, affected goats will exhibit weight loss and poor body condition scoring yet maintain a normal appetite and faecal appearance until the disease is in the very end stages and the animal is near death. Unfortunately, these signs are common to other conditions also so the only way to know for sure is to test.
For dairy goats a drop-off in milk production should also be considered an early warning sign; infected goats can appear healthy and live for years without any obvious outward indications while continuing to shed bacteria and contaminate their surroundings.
Why are young kids highly susceptible?
MAP infection typically occurs following ingestion of MAP bacteria in milk or from contact with teats or other surfaces contaminated with dung and dirty drinking troughs which can contribute to infection risk.
Once introduced, the MAP bacteria become established in the small intestine, causing it to become thickened and reducing the uptake of nutrients across the gut lining and causing the animals to slowly waste away. All the while, huge numbers of MAP bacteria are shed in the faeces into the surrounding environment to continue the infection cycle.
How else do MAP bacteria survive?
Once shed onto pasture, the MAP bacteria are resilient and survive well in damp, shaded areas for at least a year or even longer (they can only multiply inside a host).
MAP bacteria also survive well on muddy boots and tyres so it’s important to take biosecurity seriously and pay attention to cleaning, disinfection and sanitation.
Although a direct and causal link between MAP bacteria in dairy derived foodstuffs and Crohn’s disease remains unproven, ongoing debate suggests it may be timely and prudent for a burgeoning dairy goat industry to take early steps to reduce the incidence of JD on farm and to qualify absence of MAP infection in herds contributing to the production of infant milk formula where competing industries may have missed the boat.
What can we do to protect our goats?
Identifying shedders for culling and preventing newborns when they are at their most vulnerable from coming into contact with MAP contaminated faeces/milk/colostrum/ feed/water are all good ways of managing the process.
Also pay careful attention to sanitation, keep feed up off the ground where it could become contaminated with dung and keep kidding areas as clean and dung free as possible.
We recommend removing test-positive does from colostrum pools (pooled or shared colostrum is a big risk factor as MAP bacteria are shed in milk/colostrum) and keeping water sources clean (particularly those used by kids) and using waterers designed to minimise faecal contamination.
JD prevention also requires good biosecurity; if you are lucky enough to be JD free keep it that way as prevention is far preferable to control in the long run. Keep a closed herd where possible.
Always test each and every replacement (but if considering animals under one year old, better to test mum) while ideally also considering whole herd test data from the originating herd if available.
Importantly, JD is bought and paid for so don’t invite it home by purchasing live animals from a herd of unknown Johne’s status. This is because once it has been introduced JD spreads quickly and is extremely tough -- financially and emotionally -- to be rid of again.