Johne's Disease is a chronic infectious disease of cattle and is widespread within the cattle population of New Zealand.
It is caused by a Mycobacterium and the majority of infections occur in the first few days or weeks after birth. Infection most commonly occurs secondary to faecal contamination of teats, skin surfaces and feed stuffs. Other routes of infection are the ingestion of colostrum/milk from an infected cow and via the placenta to the unborn calf. The bacterium can survive in the environment for extended periods and so effluent paddocks and areas with contaminated standing water are high risk areas.
The disease has a long incubation period, so affected cows may be 'subclinical carriers' and shed the bacteria for months or years prior to showing signs of disease. Clinical signs generally appear between 4 and 6 years of age, after which the course of the disease is around 1 to 6 months.
Clinical signs include
- Weight loss &/or poor milk yield, but bright with normal appetite
- Profuse watery, bubbly diarrhoea
- Fluid collection under the jaw & brisket
Diagnosis is possible by blood test, but the tests have low-moderate sensitivity; they won't identify all infected individuals and false negative results are common. A new Milk Test is also available, which tests each individual cow at the time of herd testing. The test is best performed at a summer herd test and as an annual monitoring tool, but it can only be ordered by your Vet.
Herd management recommendations to minimise the risk of Johne's Disease
- Clean calving areas
- Pick up calves immediately (or within 12 hours) after birth; tube feed colostrum from low risk cows and rear calves on milk from these cows or alternatively, milk replacer. Thorough cleaning of the udder and teats prior to colostrum/milk collection is essential and faecal contamination of the milk must be prevented
- Prevent calves having contact with manure/dairy effluent from adult cattle
- Keep feed & water supplies free from faecal contamination
- Whole-herd testing for Johne's Disease will identify some infected individuals prior to them showing clinical signs. Removal of these animals will help to reduce shedding of the organism and spread of the disease. Whole herd testing should be repeated on an annual basis in order to pick up subclinical cases that were not identified at previous testing
- Test any suspicious cows as soon as they become apparent
- Prompt isolation and removal of any positive animals is recommended; High Positive individuals should be culled immediately as they generally start showing clinical signs within a few months
- Any High Positive/Positive individuals that are not culled should be calved separately, should not have their calves reared as replacements and should not have their milk/colostrum fed to calves
- Maintain a closed herd
Our vets are available to assess the Johne’s risk to your stock and tailor a testing and control plan specific to your farm. Please enquire at the clinic if you would like to discuss this further with a Vet.