New Zealand's effort to eradicate the cattle disease Mycoplasma bovis has made significant progress, Biosecurity and Agriculture Minister Damien O'Connor says.

The number of infected properties has dropped to new lows, three years to the day since it was first detected in New Zealand, he said in a statement.

"To date, 250 properties have been infected by the disease – with all but four now clear of it," O'Connor said.

The Government's "hard and early approach" to Covid-19 was the same response it took early on to eradicate M. bovis, "to protect our national herd, the economic base of our primary sector, and the social good of the country," O'Connor said.

It was estimated that allowing M. bovis to spread could cause $1.3 billion in economic losses in the first 10 years alone, along with substantial animal welfare issues, and serious ongoing challenges for farmers having to manage the disease within their herds, O'Connor said.

"One key measure of success of our 10-year eradication plan, the Estimated Dissemination Rate (EDR), shows strongly that we have M. bovis firmly in our sights. If the EDR is greater than one, then the disease is growing. If it's below one, we're shrinking the disease. The EDR is now at 0.4, which is down from over 2 at the start of the outbreak, so we are looking harder to find fewer infected animals.

"We've shown, again, that we're able to do what others countries have not in terms of disease eradication efforts. That's something our farming community should be really proud of."

Allowing the disease to spread would have caused lost productivity in New Zealand's cattle sectors and affected the economy, O'Connor said.

"Had we left M. bovis to run rampant, I'm not sure our dairy and beef sectors would have been able to weather the economic storm of Covid-19 and the challenges of drought conditions as well as they have."

The eradication effort had not been "without substantial challenges", O'Connor said, and the impact on affected farmers could not be under-estimated.

"Farmers deserve a lot of credit for their efforts. We are continuing to improve processes and work hard to support their wellbeing and recovery, including getting their compensation claims paid as quickly as possible."

"We are also changing tax law to further help farmers whose herds were culled. A significant tax bill can arise in the year they receive a compensation payment so we'll be making a change that means they may be eligible to spread their income over several years."

While there was still work to be done, and more infected farms to find, O'Connor said New Zealand was "well and truly on track to do what no other country in the world has done and eradicate this disease".

"The next 12 months is about ensuring that we have found all infected herds. This will involve ongoing Bulk Tank Milk Surveillance, nation-wide beef surveillance, and on-farm testing of herds that could possibly have been exposed, to ensure that they are not infected.

"We will not let up on our efforts, and will ensure that this disease is gone so that we can farm free from it in the future."