Johne’s disease is a bacterial disease caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP).
MAP can be found in the milk of infected cows, so knowing which cows are positive, or potentially positive, is important in preventing the disease from spreading in a herd.
Johne’s disease
Johne’s disease causes loss of body condition, diarrhoea, and death. There is currently no cure for the disease.
Signs of Johne’s disease:
- Reduced production, lower milk yields and lower feed conversion efficiency;
- Weight loss, despite a good appetite;
- Scour (not bloody) and ultimately emaciation;
- Soft swelling of the jaw or brisket;
- Death.
Very commonly, signs of Johne’s disease won’t actually be visible until the animal has had three or more calves.
Because of this, regular herd screening or testing is important to identify cows that are positive.
Calf removal
Calves are the most susceptible animals on a farm to the disease; even a very small amount of dung on a dirty udder can contain enough bacteria to infect a suckling calf.
The spreading of Johne’s disease from dairy cows typically occurs after the second calving or later, and very rarely before the first calving – but it can still happen.
In a herd where there is, or may be Johne’s-positive cows, the calves should be removed shortly after birth, before the calf has the opportunity to suckle the cow.
The colostrum or milk from cows that are positive or are suspected to be positive should not be fed to calves.
When collecting colostrum from any cow you should ensure that the teats have been thoroughly cleaned, as the disease is mainly spread via the faecal-oral route.
Calves will gradually acquire some age-related resistance against infection. So risk mitigation of young calves is more important during the first months, and becomes less critical as the animal ages and exceeds 12 months.