A new front in the fight against M. bovis

MPI announced on January 11 it had extended the milk testing already underway in Canterbury, Otago and Southland into a national milk surveillance programme. The new regime effectively started the day before the official announcement, with sampling packs distributed to Mid-Canterbury farmers attending two public meetings in Methven and Ashburton.

MPI says it will test three milk samples from every dairy farm in the country. One sample will be taken from bulk milk as part of the regular sampling process at milk collection. Farmers will then provide two samples, a fortnight apart, of discarded milk from cows with mastitis or other suspicious symptoms.

MPI said M. bovis is more easily identified in milk taken from already sick animals, which makes testing of discarded milk a valuable surveillance tool.

In Mid-Canterbury, the bulk milk sampling from tankers had taken place a week earlier but results were not yet available.

For the second and third phases, each of the 412 dairy farms between the Rakaia and Rangitata Rivers was given its own individually labelled sampling pack consisting of a small chilly-bin, cooling pad, collection jug and sample vials. 

The milk companies Fonterra/MyMilk, Synlait and Westland were to distribute the packs to farmers who did not get to either of the two well-attended meetings.

Farmers were to collect milk from every quarter of every cow that appeared to be off-colour for any reason, on January 17, and place a vial of the sampled milk in the chilly-bin for collection by their tanker drivers. They would repeat it two weeks later, on January 31.

Asked if the programme was voluntary or mandatory, Fonterra’s general manager of veterinary, technical and risk management, Dr Lindsay Burton, told the Ashburton meeting “I don’t do voluntary”.

District by district, the whole exercise will roll out across the country in the next couple of months.

Burton told the meeting that it is important to know the status of every herd in the country to identify all possible clusters of the disease.

 He reminded farmers that only New Zealand and Norway, of all developed milk industry countries, do not have M. bovis established. Everyone else had “given up” testing for it, which meant NZ had to develop its own testing regimes.

Burton said antibody testing had proved “not useful” because of false positives from other, unimportant, mycoplasmas. The national testing programme will use PCR testing, a method of fingerprinting DNA from extremely tiny samples.

MPI response coordinator David Yard assured farmers that the ministry had not been sitting on its hands. 

Since the first detection of M. bovis on  a Van Leeuwen Dairy Group farm near Oamaru in July, MPI has had nearly 200 staff “working flat out”. MPI and commercial labs had done 65,000 tests and the nationwide scheme would produce another 36,000. 

It is vital to know all animals’ movements, both on and off infected farms, said Yard.

“To date we have looked at more than 400 trace properties. I describe this as a spider web because for every positive property we get, there’s probably 30 or 40 trace properties that have either been supplied with or given animals away. So one farm becomes 40 and those 40, if you multiply it, becomes a huge number.”

Yard said further positive results were expected but it was wrong to say the disease was getting away. MPI believed the disease was not long established.

“I give you my word... the aim at the moment is eradication,” he said.

Another MPI Vet, Dr Kelly Buckle, said that when the disease was found MPI could not immediately do bulk milk testing but instead did “syndromic surveillance”, asking vets throughout the country to phone in instances of unusual arthritis or mastitis. 

That resulted in hundreds of reports but all except one – a farm that was also a trace property – proved negative. They also paid special attention to large herds, where the disease spread most easily, again with negative results.

“So we really would be surprised – we would be enormously surprised, I think – if we found this thing was widespread. But we owe it to everybody to find out what the real state of play is before we continue on this,” said Buckle.