The Northland farm that is infected with Mycoplasma bovis is east of Dargaville and the farmers bought the infected animals from Canterbury.
The revelation was made at Mycoplasma bovis information meeting organised by the Ministry for Primary Industries at Dargaville's Northern Wairoa Hall today.
The meeting was organised after the first confirmed case of M. bovis was found in Northland last week.
MPI had so far not revealed where the infected farm was, but it emerged at the meeting that the farm was at Arapohue, east of Dargaville.
The farm owners are devastated by the news and the meeting heard that they bought a small herd of friesian yearlings from Waikato that had come from Canterbury between January and March last year.
Earlier this year some of the animals suffered from theileria - a tick-borne disease caused by an intracellular blood parasite. Normally cows in Northland can recover relatively easily from the disease, but when the animals did not get better Dargaville Vets were contacted.
As the animals were not getting better M. bovis was suspected as cows with the infection cannot recover from diseases such as theileria as easily and MPI was notified.
A small number of the animals were euthanised and samples taken from the animals' throats and M. Bovis was confirmed last week.
A number of questions from the audience today concentrated on the belief that MPI was not doing enough to stop "rogue" stock agents from moving cattle around to bypass MPI M. bovis controls.
Dargaville Vets manager Brian Lowe said there were truck and trailer loads loads of cattle were being brought from Canterbury to sell in Northland, because they were cheap to buy.
''It's a major concern.''
Lowe said this should not be allowed as Canterbury, with 32 farms infected by M. bovis, had the largest number of infections in the country.
MPI has assured Northlanders that livestock not in close proximity to a farm in the region infected with M. bovis are not at risk of the disease.
The infected farm, with about 50 beef cattle, tested positive for the bacterial cattle disease last week - the first time M. bovis has been found in the region.
Today's meeting was to help the community better understand the disease, response activities, and to ask questions of Biodiversity New Zealand.
"M. bovis is not a disease that spreads on wind or water, it is a very slow moving disease that is spread through prolonged and repeated cow-to-cow contact or through drinking infected milk," an MPI spokeswoman said.
She said MPI's quarantine measures were very effective in containing the disease and mitigating its spread.
The infected property in Northland is in quarantine lockdown to reduce the likelihood of the disease spreading. All infected cattle on the farm will ultimately be culled, in agreement with the farmer.
MPI has informed all immediate neighbours so they can take the necessary precautions to stop their cattle coming into contact with animals who may be carrying the infection.