Johne's Disease - An Introduction
What is Johne’s Disease?
Johne’s disease is an infectious bacterial disease of cattle and other ruminants. Cattle usually become infected during the early weeks of life following the consumption of milk or food contaminated with the bacteria, which are shed in the dung or milk of infected adult cattle. On occasion calves born to infected dams can also become infected in the womb, particularly where the dam has advanced disease. Infection develops slowly and the signs of disease vary depending upon the stage of infection but begin with reduced productivity followed by weight loss, scour and ultimately emaciation and death.
How is it spread?
Infection is usually introduced onto a farm through the purchase of an infected animal. The other main route of introduction is through infective material brought onto the farm e.g. colostrum or slurry, particularly when this is spread on pasture grazed by younger animals.
How can it be controlled?
Once infection is present on a farm it is important to limit the exposure of calves to the bacteria that cause the disease through removing the sources of infection and maintaining excellent calf hygiene standards. Any animals that are shedding the bacteria should be culled. Infected animals that test positive on blood or milk are more likely to be shedding the bacteria in their faeces, and these animals should therefore be prioritised for culling. A high level of hygiene within the calf environment is crucial, i.e. calf areas must be kept clean and free of adult cattle dung. Importantly, the bacteria can be transmitted in colostrum and milk; both through the direct excretion of the bacteria into the milk of infected cows and the contamination of milk with faeces e.g. dung contaminated teats. For this reason, the use of colostrum or milk from infected cows or cows of inconclusive infection status should be avoided. This includes avoiding the use of milk and colostrum pooling where any of the sources could be cows that are infected.
As part of the anticipated National Voluntary Control Programme for Johne’s Disease, Animal Health Ireland is now running training for veterinary on-farm Risk Assessment & Management Planning (RAMP). Interested practitioners can click here for further information.