Johne’s disease is a bacterial disease of cattle, which can have a negative economic impact on farms. It is also known as paratuberculosis.
Infection normally occurs when young calves drink colostrum and milk or eat fodder contaminated with the bacteria. Contamination arises when infected dung or milk of infected cattle is ingested.
In addition, an infected calf can also infect other calves that are housed in the same pen. According to Animal Health Ireland (AHI), the disease progresses slowly and is incurable.
However, in August of 2017, the Johne’s Disease Implementation Group agreed the commencement of a new programme for the control of Johne’s disease in Ireland.
Indication of the disease will depend on the stage of infection; how many bacteria the calf swallowed; how soon after birth they were ingested; and how quickly the gut wall has become damaged.
The signs of infection normally become evident gradually. Tell tale signs normally include: a reduced feed conversion; weight loss; scour; and death.
Despite this, according AHI, it is not uncommon for indications that the animal has Johne’s disease to remain invisible until the cow has had three of more offspring.
Control of the disease
Infection of an existing herd can come about through the purchase of an infected calf, cow or bull. However, infection can also occur from contaminated colostrum or slurry purchased from another farm.
According to AHI, once infection is present on a farm, it is important to limit opportunities for calves to swallow the bacteria by removing the sources of infection and maintaining excellent standards of calf hygiene.
Any faecal-positive animals should be selected for culling and kept well away from calves before they leave the farm.
In addition, AHI says, by the time an infected animal tests positive in blood or milk, it is highly likely to be shedding the bacteria in dung and milk and these animals should therefore be prioritised for culling. If they remain in the herd they are a source of contamination.
Furthermore, keeping a closed herd can be very advantageous. Farmers rearing their own stock have the best chance of keeping Johne’s disease causing bacteria free from the herd.