The $60 million cull of 22,000 cattle infected with disease Mycoplasma bovis is underway, the Minister of Agriculture has confirmed.

Damien O'Connor told reporters on Tuesday that support was being offered to farmers from 22 properties in Hawke's Bay, Canterbury, Otago and Southland who have cattle that must be killed to prevent the disease spreading further.

"We need to reduce the risk of any spread of this infection throughout the country," he said. Under the Biosecurity Act, farmers from infected properties will be entitled to compensation, which could cost $60m, O'Connor said.

Operating costs for investigating and stopping the disease spreading for the Ministry for Primary Industries have been more than $35m to date, but ongoing costs of eradicating Mycoplasma bovis fully from New Zealand had yet to be fully calculated, he said.

"There will be fair compensation for farmers - every animal is priced differently, with different production potential, so there is a process to go through," O'Connor said. There was no issue with New Zealand's cattle numbers, O'Connor said.

Better compliance to the National Animal Identification and Tracing programme - it is as low as 30 per cent in some parts of the country - along with changes to farming practices and biosecurity measures was needed in order to protect the country's farming future, he said.

O'Connor hoped the origin of Mycoplasma bovis would be found eventually. It was spread mainly through cattle movement and he reiterated there was no threat to humans from the disease. Federated Farmers president Katie Milne says news of the cull was a relief for all farmers.

"Their [MPI] determination to do the best we can to get rid of it should be acknowledged by all farmers," she said. Ms Milne said it was important families affected by the cull be offered as much support as possible.