With over two thirds of the UK’s dairy herds harbouring Johne’s Disease, many of you will be all too familiar with this frustrating disease. We’ve seen the set up and implementation of Action Johne’s Management Plans over the past two years and with the plans implemented we should be getting a better handle on Johne’s in our herds. However, with further Johne’s targets recently being announced from Tesco, we must continue to tackle this complicated disease and work with the management plans we have put in place.
Clinically, many of us will be familiar with the signs encountered in the later stages of this untreatable disease. These signs typically show in cattle of three to five years of age, although they are not limited to this age group. At the point that we see these signs, severe irreversible damage has occurred to the lining of the gut. As a result the intestine becomes leaky and the animal loses large amounts of protein and water resulting in severe diarrhoea. Initially, this scour can wax and wane but, as the diarrhoea becomes chronic, it is followed by dehydration, weakness and weight loss, to the degree that euthanasia is the only option.
Despite these severe clinical signs, infected animals do not tend to show the typical signs we associate with bacterial infection such as them going off their feed or having high temperatures however due to fluid loss, they can drink excessively.
Johne’s is a frustrating disease. To reach the point at which severe symptoms are apparent, the disease has progressed through a number of stages over a typical period of 2-4 years. So, by the time a cow has shown symptoms, she could have bred three youngstock into the herd. This is what we call the ‘iceberg effect’ referring to the undetected presence of an estimated twenty infected animals that are yet to display clinical signs for each clinical case observed.
With a vaccine that has severe limitations in relation to implementation and TB testing, consistent management is key to getting on top of Johne’s. We will have run through each of the management strategies with you and started you on a plan which is most appropriate for your status and herd. However, in general
terms both surveillance testing and improved farm management must be adopted together. A range of relatively cheap but effective diagnostic tools are available that can be used to monitor the infection in both individuals and across the herd as a whole. These can be carried out using a number of sample types including blood, faeces and milk.
It’s unusual but not impossible that a clinical case will come back as negative from milk sampling and we have had recent examples of this. What we must remember is that all testing has its limitations. For example, using a faecal sample to identify a Johne’s positive cow should really only be used for suspicious cows. This is due to the fact that MAP sheds intermittently.
Working closely with your vet in these circumstances will help manage the positive cows in the herd – this is especially relevant to Tesco producers who now have a “less than 2% red” target to hit by July 2021. If you’re at all concerned, please speak to your vet as soon as possible.
In addition to testing, typical management controls include only feeding colostrum and milk from cows that have consistently tested negative for Johne’s, serving infected cows to a terminal sire, housing and calving infected cows separately and ultimately culling infected animals at the most appropriate time.
Estimations suggest that two thirds of UK herds are infected with MAP. This may well be an underestimation however if your herd is lucky enough to have avoided infection to date, the message is simple – keep it out! Ensure that strict biosecurity policies are in place and that all bought in animals (including bulls) are sourced from low risk herds and keep monitoring through routine testing.