Johne’s disease, caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP), can lead to severe economic losses for dairy farmers due to decreased milk production, weight loss, and eventual culling of infected animals. Here, Rob Hall, Veterinary Surgeon at LLM Farm Vets delves into what Johne’s disease is, how it affects cattle, and what dairy farmers can do to protect their herds.
Johne’s disease primarily affects the small intestine of ruminants, causing inflammation which thickens the gut wall and therefore prevents absorption of protein. This disfunction of the intestines leads to weight loss and diarrhoea in the final stages of the disease. However, earlier stages of the disease are linked to milk production losses and increased risk of mastitis, lameness and sub-fertility. Ultimately, the disease increases culling rates and mortality of severely affected cows.
The bacteria responsible for the disease can survive for long periods in the environment, making it highly contagious and difficult to eradicate once it’s established within a herd. Infected animals typically shed the bacteria in their faeces, contaminating the environment and serving as a source of infection for other cattle.
Over two thirds of dairy herds are affected by the disease, which has been identified as the fourth most costly disease for the dairy industry (behind lameness, mastitis and TB)1.
Johne’s is considered an ‘iceberg disease’ – for every cow which becomes clinically affected with weight loss and scour, there are at least 4 more lurking under the surface who are already infected and shedding MAP in their faeces.
The cost of the disease is estimated at £2600 per 100 dairy cows, based on clinical cases. Without accounting for the additional associated disease, this is likely to vastly under-estimate the true cost of the disease to a farmer.
The National Johne’s Management Plan sets out six control strategies which farms can adopt. Herds which have no evidence of Johne’s disease after repeated screening should focus on strict biosecurity to keep the disease out.
For herds with the disease, there are two main components to disease control:
The most commonly test used is the milk antibody ELISA, performed on individual samples by milk recording organisation. Repeat testing is required due to the low sensitivity of the test, meaning it has a poor ability to identify infected animals, especially earlier in the progression of the disease.
Younger animals are at greatest risk of acquiring the infection, with 80% of cases originating in the first month of life. Milk and colostrum can contain MAP bacteria, however calves consuming infective faeces is by far the most common route of infection. This is mainly through “one to many” transmission – one heavily infected cow can shed huge amounts of the bacteria in her faeces, contaminating the entire calving yard. Don’t forget that this is a place which all calves pass through! There are many ways to reduce calving yard contamination: more frequent cleaning; individual calving boxes; having a separate sick-cow yard; calving positive cows separate, or (even better) culling them before they get chance to spread the disease.
The Johne’s Progress Tracker reports, available through your vet or milk recording organisation, provide a useful benchmarking tool for assessing the success of your Johne’s control strategy. Colour coding shows how your performance stacks up – red, orange, light green, dark green – show your position compared to the worst to best quartiles.
The tracker looks at metrics for Progression (whether cows succumb to the disease at a young age); Persistence (how many repeat positive cows are in the herd); Removal (quickly you cull repeat positive cows); Service (how likely confirmed positive cows are to be re-bred); and Disease Level. The report provides a good starting point to reassess your Johne’s control plan.
Working with your local vets practice and industry experts is essential to develop and implement effective disease prevention and control strategies tailored to the unique needs of each farm. Through diligent management and vigilant monitoring, dairy farmers can work towards maintaining healthy and productive herds in the face of an old foe, Johne’s disease.
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