A third South Island farm is in lockdown after some of its animals tested positive for the Mycoplasma bovis cattle disease.
The Ministry for Primary Industries said blood test results from the property showed some animals had been infected.
This is the first case to be found outside of the Van Leeuwen Dairy Group, where the disease had been contained up to this point.
The highly contagious disease causes mastitis, pneumonia, abortions, lameness and death in cattle.
The ministry said the new property was in the Oamaru area and had direct contact with one of the infected Van Leeuwen farms before the outbreak happened.
MPI response director Geoff Gwyn said the property had been on the ministry's radar for some time.
"I don't find it surprising ... this is a trace that we've been speaking to for the last three weeks, it's just taken a little while for the testing to be completed."
The ministry said no animals have left the farm since 20 July, but before then some animals were shifted to other farms and the ministry was now contacting those properties urgently.
Mr Gwyn said no other tests have come back positive from its surveillance testing scheme.
The farm has not been named and neighbouring farmers have told RNZ that the ministry should tell people which property was infected, so they could check their own stock movements.
However, Mr Gwyn said they would not be disclosing which farm was infected.
"No, we won't be for privacy reasons, but what I can assure them is we're in contact with the 14 farms that have had stock moved from this particular farm onward."
Farmers in the region also wanted to be told which properties have had test results back and what they were.
But Mr Gwyn said privacy was more important than the outbreak.
"From our perspective we deal with the farmer concerned, we're not prepared to go out and identify, for obvious privacy reasons, all the farms we are talking to."
He said the fact it was an outbreak did not override privacy issues.
"I think we are taking sensible risk mitigation measures.
"I have a high level of comfort that the farms we need to restrict movements on we have, which at this stage is only the three."
The outbreak was first detected in late July, when the disease was found on two of the 16 Van Leeuwen Dairy Group farms in South Canterbury.