…also known as MAP, the bacteria which causes Johne’s Disease.
This small bacterium was first described in the late 19th century. Initially it was believed cattle were the sole hosts but we now know MAP infects a range of other species including sheep and goats.
Many of you will be familiar with the signs encountered in the later stages of this untreatable disease. These signs are usually seen in cattle around three to five years old but are not limited to cattle of this age. At this point, profound irreversible damage has occurred. This is through a combination of the activity of MAP invading the lining of the intestine and the associated host’s immune response to this microbial invasion.
As a result, the intestine becomes leaky and the animal loses large amounts of protein and water resulting in severe diarrhoea. 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. For example, going off their feed or having high temperatures. However, due to severe diarrhoeic fluid loss they can drink excessively.
To reach the point at which severe symptoms are apparent, the disease has progressed through a number of stages over a typical period of two to four years. Based on the long lag period, the pattern of disease progression has been described as the ‘iceberg effect’. This refers to the undetected presence of an estimated twenty infected animals that are yet to display clinical signs for each clinical case observed.
Infection occurs most commonly in calves and youngstock through ingestion of faeces containing MAP. Newborns are particularly susceptible to infection. Just tiny amounts of faeces are capable of transmitting disease. This is of particular concern as newborns can easily ingest these levels of infective material during calving. This is from the environment, or probably most importantly through feeding contaminated colostrum. For this reason feeding of pooled colostrum should be avoided.
Whilst faeco-oral contamination of the newborn is the predominant method of disease transmission, it has been reported that there is a small but nonetheless significant risk of transmission to the calf during pregnancy.
We should be worried about the presence of Johne’s in our herds for a number of reasons. Johne’s infection has a negative impact on a range of factors including:
- milk production
- feed conversion
- cull value
- somatic cell count
- as well as more broad factors such as general health and longevity.
Rate of spread
The potential rate of spread of uncontrolled Johne’s infection within a herd is a huge risk to it’s future viability. More recently, however, MAP has come into the spotlight from a public health point of view. There are a number of reports associating the organism with Crohn’s disease in humans. Not surprisingly food processors are therefore showing greater interest in the potential role MAP could play in Crohn’s!
Estimations suggest two-thirds of UK herds are infected with MAP. This may well be an underestimation, however, and if your herd is lucky enough to have avoided infection to date, the message is simple – keep it out. Ensure strict biosecurity policies are in place. Additionally all bought-in animals (including bulls) should be sourced from low risk herds and keep monitoring through routine testing.
The National Johne’s Management Plan (NJMP) Strategies
You will now have had a Johne’s review as part of your health plan and we will have gone through the six NJMP strategies with you.
Optimal Johne’s control strategies will be specific for each 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.
Furthermore, these can easily be applied to samples taken at routine milk recording. These can be used to not only identify but to track disease progression in individuals infected with MAP. Thus providing a greater understanding of the herd status.
High-risk animals identified in these screens can then be closely managed to control further spread within the herd. The prevalence of this condition can be controlled and a number of resources are available with the national Action Group on Johne’s providing good general advice (www.actionjohnesuk.org).