Johnes disease is a chronic infectious disease of cattle (and other ruminants) characterised by diarrhoea and wasting. It is caused by the bacteria Mycobacterium avium subspecies paratuberculosis .
Johnes is a poorly understood and often largely ignored disease due to its slow onset and long incubation period but it can be costly in terms of production losses and premature culling of animals.
There is also an increasing concern to food safety authorities and the consumer public with the similarities between Johnes disease in cattle and Crohn’s disease in humans. There is ongoing debate as to whether there is an identifiable link between these two diseases.
It is generally accepted that calves are infected before or at birth or can be infected up until about 12 months of age when they become more resistant to becoming infected. They are most likely to be infected in the first few days or weeks of life by:
1) Transplacental infection from infected mothers
2) Drinking infected colostrum or milk
3) From faecal contamination of teats, grass, or water
4) By the respiratory route.
The most important and common route of infection is 3) the faecal/oral route.
After infection there is a long incubation period and it is not until around 3 years of age or older that cows will become “clinical”; losing weight, dropping production and a profuse scour (sometimes referred to as a “pipe scour”). This scour ends up shedding large numbers of bacteria especially after a period of stress, (e.g. Calving) which then contaminates the environment.
As the disease progresses the lining of the bowel becomes thickened resulting in malabsorption of nutrients with fluid and protein loss from the bowel.
With Johnes disease; cows aren’t usually “off colour”, generally have a normal appetite, and are bright until the latter stages which can be 1 to 6 months or longer.
The number of cows showing clinical disease is generally a small percentage of the total number of animals infected with the bacteria.
There are no effective treatments for Johnes disease so once a diagnosis is made the animal should be culled to limit the contamination of the environment and spread to other animals-especially calves.
Testing of individual animals can be done by blood test or herds can be screened by an individual cow milk test with a follow up blood test for those found to be positive or suspicious on milk test.
Control of Johnes is best achieved by:
1) Early identification and elimination of infected animals
2) Reducing faecal/oral spread by having clean calving areas, not allowing or limiting time that newborn calves can suckle from their mothers, feeding colostrum from low-risk cows, ensuring feed and water is not contaminated with faeces, and limiting calves’ contact with cows’ faeces (effluent paddocks).
3) Management of milk and colostrum intended for consumption by calves either by the use of calf milk replacers or by the use of colostrum and milk from low-risk cows after thorough cleaning of the teats and udder before milking.
If you feel that Johnes Disease could be a significant problem in your herd with a number of fading and scouring cows then contact us to have a chat and make a plan.
