All cattle infected with mycoplasma bovis are to be culled at a total cost to the government of about $60 million, MPI has announced.

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The Ministry for Primary Industries said the cull of just over 22,000 cattle on 28 infected properties in the South Island would begin shortly.

MPI's response director Geoff Gwyn said it was a big job and would not happen overnight.

"But we'll be meeting with the affected farmers in the coming days to discuss the operation, develop the plans and talk through compensation."

"The de-population of entire herds on all 28 Infected Properties (IPs) in New Zealand is a critical measure to control the spread of the disease and we will be working closely with those farmers to plan how this will happen,"

MPI said affected farmers would be compensated for their verifiable losses.

"We understand this has been an incredibly difficult time for farmers while they wait for critical decisions to be made about managing and controlling this disease," said Mr Gwyn.

"This cull will give those farmers back some certainty and control over the future of their farms, their animals and their livelihoods.

"We are able to take this decision now because we are confident Mycoplasma bovis is not well established in New Zealand.

Minister of Agriculture and Biosecurity Damien O'Connor said it was estimated the cull and associated management, testing and tracing and full compensation would cost about $60m.

"It is a lot of money, this is a very serious disease. If we can't get control of it, it has huge impacts on not just the dairy but the drystock industry.

"So we've been focusing on eradication, on the necessary steps, and the decision today is one of those necessary steps."

He said the cull was a critical measure to control the spread of the disease and would hopefully be completed by the end of May.

"It has taken some time to get to this point," he said.

"The previous National Government ignored the known deficiencies of the NAIT system and was slow to react to the initial discovery of Mycoplasma bovis."

"Everyone across New Zealand can understand how incredibly difficult it is for these farmers to lose their herds - many of these animals will be known individually. While we still have challenges ahead in managing this outbreak, these families can move forward with their farms and lives."

"By making this cull, we believe we significantly reduce the infection load.

"To this point we didn't know whether the disease was endemic through New Zealand and therefore would have been virtually impossible to eliminate.

"We're now making this call, we hope we can eradicate, and this is the first major step."

Federated Farmers president Katie Milne said the decision was to be applauded, and showed the government was committed to eradicating the disease.

She called on family, friends and communities to rally around affected farmers to support them at this difficult time.

What we know about the disease