How can Johne's disease be controlled?

It’s all about keeping dirt away from the calf. 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. The more successfully this is done, the fewer calves will be infected and the healthier they will be.

Any faecal culture or PCR-positive animals should be selected for culling and kept well away from calves before they leave the farm.

By the time an infected animal tests positive on 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 since while they remain in the herd they are a source of contamination of the calving environment. It is important to keep the calving pens and calf-rearing areas of the farm separate from each other and clean. Remember, a high standard of hygiene within the calf environment is crucial, ie calf areas must be kept clean and free of adult cattle dung.

Animal Health Ireland (AHI) suggests that these measures will not only help protect them from Johne’s disease but also from other bacteria and viruses, particularly those causing diarrhoea and pneumonia. Importantly, the bacteria causing Johne’s disease can be transmitted in colostrum and milk, both through the direct excretion of the bacteria in the milk of MAP-infected cows and the contamination of milk with faeces, eg dung-contaminated teats.

For this reason, the use of colostrum or milk from infected cows, or ELISA-positive cows, which are yet to have infection confirmed with a faecal culture or PCR test, should be avoided.

Investigating test positive animals

Whole herd screening tests using the ELISA test are a valuable method for the early detection of Johne’s disease in a herd but repeated testing at regular intervals on all animals over two years of age in the herd is best.

Animals that return positive ELISA results pose a challenge, since some of the animals will be in the early stages of infection, and others may be false positives. Ancillary testing focuses on the individual test positive animal, rather than the whole herd, and uses a dung sample instead of blood or milk. There are two tests recommended as ancillary tests; the faecal culture test and the PCR test.

A positive result from either of these tests confirms infection in the animal and the herd.

The management plan your vet provides as part of the on-farm risk assessment (VRAMP) will assist you to put in place the necessary practices to minimise further disease spread within your herd and reduce the risk of further faecal shedding and environmental contamination.

Ancillary testing assists vets and farmers to identify animals which are infected.

Without this additional testing, the advice is to manage all animals that return positive test results as if they were infected, and to keep them away from young stock and calves, and areas where young stock and calves are housed or fed.

This cautious approach is warranted given the consequences of an infected animal contaminating the farm environment by shedding bacteria. An animal that returns a negative ancillary test result is described as having an inconclusive disease status until the animal is tested again as part of the next whole herd screening test.

This is because the animal could be in the early stages of the disease process where bacterial shedding is low and intermittent, with the result that bacteria may not always be present in the dung sample at this stage.

Ancillary testing is a useful next step in a herd investigation for Johne’s disease, and one in which test interpretation should be provided by your veterinary practitioner.

The new Johne’s national control programme has finally got the green light. AHI is set to follow up on a pilot phase which ran between 2014 and 2016 with two new phases of a new Johne’s management programme.

The first phase is set to start immediately for those farmers who were originally involved in the pilot programme and phase two is set for an early 2018 start. The implication for farmers is that herd testing for Johne’s will effectively be subsidised. The exact subsidy has not yet been decided.

Phase one of the new programme (September to December 2017) will include recommendations from an Australian consultancy firm on what model of Johne’s control is suitable for Ireland. Recommendations from this report will form the basis of how phase two (2018 to 2023) will operate.

The Australian consultant report will include details around what frequency of testing is best for Ireland, what other information is worthwhile such as cull cow screening and what steps farmers must take if they have Johne’s-positive animals.

A national awareness programme is scheduled for autumn 2017.

Phase one of the new programme is set to include the 1,800 mostly dairy farmers who were involved in the pilot programme.

Phase two in 2018 will be open to all farmers, including those with dairy and suckler operations.

Funding for the programme will be sourced from the dairy processors, farmers and the Department of Agriculture. The implementation group of AHI will decide exactly how the programme will operate nationally in early 2018.

Farmers need to ask themselves key questions about management of Johne’s disease on farm. The comments explain the reasoning behind the question.

1. Are calves fed colostrum from own mother or from known low-risk colostrum cows or artificial colostrum (recommended only in emergency situations)?

Feeding “own mother to only one calf” helps prevent the spread of Johne’s. ‘‘Clean colostrum’’ refers to colostrum which has not been contaminated by faeces; the cleaner cows are at calving the less likely it is to be contaminated.

2. Are at least three litres of colostrum (first milking) consumed within the first two hours?

Feeding calves at least three litres of clean colostrum within the first two hours is recommended.

3. Are calves fed on low-risk whole milk, pasteurised low-risk milk or milk replacer?

Low-risk whole milk comes from cows selected on their perceived Johne’s infection risk. In the absence of testing, some farmers may select to feed milk only from younger cows or cows known not to have Johne’s-infected relatives, which should be lower risk for milk transfer of Johne’s. Milk replacer is unlikely to contain Johne’s, but can become a risk if it is mixed with manure-contaminated water or fed in manure-contaminated buckets or bottles.

4. How often is non-saleable whole milk (high-risk) fed?

Non-saleable milk is milk that is not suitable for sale for milk processing, eg mastitis milk, high SCC, transition milk or antibiotic milk.

5. Are calves housed in individual pens or in groups for the first week?

There is evidence that in highly stocked pens other potentially clean calves can become infected if calves that have been infected are housed with them.

6. Is there exposure to cow manure in calf housing or grazing area?

Young, milk-fed calves can ingest Johne’s from cow manure if it contaminates bedding, alleyways, grazing areas, roadways, feed and water.

7. Is there exposure to cow manure by water or feeding utensils?

Calves can be directly exposed to Johne’s if feeding hygiene is not excellent. Using contaminated water for mixing milk replacer or for calf drinking can increase exposure.

8. Are calves fed forages that have received slurry from adult animals within the last year?

Slurry may be a potential source of Johne’s. The evidence for the degree of risk is not clear. It is frequently of concern to farmers or managers and calves are the most vulnerable group.

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