A key role for veterinarians is to educate farmers about risk factors that make them vulnerable to M. bovis. This conversation will flow out of the risk assessment as farmers are made aware of what their on-farm risk behaviours and practices.
While the key risk factors have been well publicised by MPI and the industry, it is useful for veterinarians to reinforce them when talking with farmers.
Key Points for Discussion on Minimising Risk
Farmers should limit cattle movements onto their farms and avoid their animals coming into contact with their neighbours’ animals. Double-fencing all boundaries and ensuring they are stock-proof, is a sensible pre-caution. Accurate NAIT is required, and animal movement history should be considered before new stock is introduced. See above for more information.
Feeding raw milk
Milk from infected cows that is fed to calves is the other key risk factor in transmission of M. bovis. NZVA advocates for no between-farm milk movements. This is key to reducing transmission of M. bovis because milk movement is not currently recorded in New Zealand, and therefore presents a real challenge in the response tracing. If milk is transported between farms, NZVA strongly recommends that movement between farms is always linked to calf movement between the same farms– in other words, calf NAIT tracing will be a proxy for waste milk tracing (which is currently unregulated and untraced) and the risk profile for farms would be the same. Ideally farmers would only feed milk from their own farm to their own calves.
Introduction of milk from outside sources should be considered very carefully – cows shed M. bovis intermittently so prior bulk milk results are not a robust way to gauge a farm’s status, and even less so a cow’s individual status. Shedding is more likely at times of stress (i.e. during transition).
Transportation of infected cattle remains the greatest risk of disease spread, but the contaminated trucks are also present a small risk regarding spread of disease. Disinfection is only effective in the absence of organic matter. Therefore reducing risk is a two-step process – first thorough cleaning, then disinfection.
The most important thing to do is hose all the mud, faeces and urine out of the trucks and let all surfaces dry. Sunlight and desiccation destroy Mycoplasmas, so with good cleaning, drying and then disinfection there is little chance Mycoplasma bacteria will survive. Ideally, trucks should be thoroughly cleaned between loads from different farms, particularly those under legal notice. It is not necessary to clean between loads from the same farm. Trucks should be cleaned and disinfected at the end of the day.
What this will mean in practice is multiple consignments on one truck should to be avoided.
Farmers should be instructed to minimise the number of trucks used to cart stock, For example, using one truck all day for one property rather than 5 trucks over a couple of hours, and then going to the next farm. This limits the C&D required and minimises costs for the trucking company. Trucks should then clean and disinfect before the next property.
With the above in mind, calf days do present some challenge – on first principles, they involve movement of animals and this should be carefully considered prior to being undertaken. For transmission of disease, M. bovis requires prolonged (undefined), close contact of a susceptible host, with an animal that is shedding.
If pet days are to go ahead, and include calves, things to consider are NAIT records, and likely farm risk, ensuring animals are not mixed, preventing close contact, avoiding sharing of milk and other equipment (e.g. grooming brushes, halters). Fomites are important when considering other diseases (e.g. ringworm), so personal hygiene, including hand washing and not sharing equipment, should be encouraged.
In all likelihood, in a low-risk area, in a well-managed environment, risk of disease transfer at a pet day is probably very low. In the hot spots, careful consideration would be prudent. During the current eradication phase, NZVA advocates calves are not taken to pet days.
Muddy tracks and trucks
Disinfectants won’t work through dirt – farmers need to remove all organic matter from gear and vehicles BEFORE they disinfect. Once items are clean, using a disinfectant is only useful if mixed correctly and correct contact time is achieved. With some disinfectants, this may be up to 10 minutes.
Cleanliness and good hygiene practices are good general biosecurity tools with which all farmers should engage, and veterinarians should encourage and drive these conversations.
However, risk of transfer of M. bovis by mud, indirectly, is very low. Other risks (milk and animals) are far more important and this needs to be communicated to farmers. We shouldn’t be overly alarmed about muddy tyres, but we should be alarmed about indiscriminate movement of milk and animals.