The Mycoplasma bovis culprit was unlikely to be found, investigators said in June.

Farmers are failing to report livestock trades where the Mycoplasma bovis is suspected, the Ministry for Primary Industries says.

Director of MPI Geoff Gwyn said the number of proactive reports from farmers of suspected disease and suspect trace movements has not been overwhelming.

"Since the Mycoplasma bovis response began in July 2017 MPI has received almost 200 calls to our pests and diseases hotline," he said.

ROSS GIBLIN/STUFF MPI director Geoff Gwyn said a poor response from farmers is making investigations difficult.

"But the vast majority of these phone calls have been from veterinarians and not from farmers."

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However, Federated Farmers president Katie Milne disagreed and said farmers were using a variety of ways to report issues.

JOSEPH JOHNSON/STUFF Federated Farmers president Katie Milne says the current tracking system needs to be better enforced to ensure herds are protected.

"I know multiple farmers that have contacted them, maybe not through the MPI's 0800 number, but through Federated Farmers or quality assurance."

Federated Farmers has given MPI a lot of intel over the past year which would dispute the assertion farmers weren't being proactive, she said.

There are currently 38 'active' infected properties following confirmation two new farms were added to the list on Friday - a dairy farm in Waikato and Hawke's Bay beef farm.

HEATHER CHAMBERS/STUFF In response to the outbreak of mycoplasma bovis, farms are asking visitors to pass through a disinfecting foot bath, like this one in South Canterbury.

So far over 24,000 cattle have been culled in the fight against the disease.

During an interview with RNZ on Friday, Gwyn referred to an MPI investigation into calf movements off a farm in Southland.

"We called for information about these animals and even put advertisements in the local paper. We had no response in the months after."

But Milne suggested some farmers failing to properly track livestock trades on the NAIT (National Animal Identification and Tracing) system has made it difficult for other farmers, as well as MPI investigators.

"Early on MPI thought it started on one farm, it wasn't clear who needed to put their hands up initially."

Because some farmers are not registering livestock, it means others may not know part of their herd had come from that farm, she said.

"The NAIT system needs to improve going forward, and farmers are desperate for that to happen.

"Buyer beware is the most powerful tool to protect for many concerns - not just Mycoplasma bovis, but tuberculosis and other issues."

The NAIT system was introduced to New Zealand over six years ago, and should essentially provide a tag for any animal moving from a property.

"Truck drivers should not be picking up any stock from any farm without the correct tags.

"Federated Farmers will back any truck driver who refuses to pick up animals without tags."

The regional breakdown of affected properties is available on the MPI website.