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.
An online tool for assessment of M. bovis risk (the Dairy Risk Assessment tool, developed by XLVets) has been distributed by the NZVA. This tool is designed for use by veterinarians in consultation with their dairy farming clients, and generates a risk 'score' based on farm management practices known to be a risk for spread of M. bovis. Veterinarians are then able to give specific advice to help farmers reduce their risk. Find out more on our website at https://www.nzva.org.nz/page/dra.
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 M. bovis risk
Farmers should limit cattle movements onto their farms and avoid contact with neighbouring 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.
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. Multiple consignments on one truck should to be avoided. It is not necessary to clean between loads from the same farm.
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. Trucks should then clean and disinfect before the next property.
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.
Ideally farmers would only feed milk from their own farm to their own calves.
However, if milk is transported between farms the NZVA strongly recommends milk movements are 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.
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).
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.
In a low-risk area, risk of disease transfer at a pet day is probably very low with appropriate management. In the hot spots, careful consideration would be prudent. During the current eradication phase, NZVA advocates calves are not taken to pet days.
Further information on pet day biosecurity can be found on the MPI website.
Muddy tracks and trucks
Disinfectants won't work through dirt - it is necessary to remove all organic matter from gear and vehicles BEFORE attempting disinfection. 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.
Further information on farm biosecurity can be found on the MPI website, the DairyNZ website and the Beef+Lamb New Zealand website.