"If MPI plays secret squirrel, how on earth are they going to manage or mitigate the risks.
There may be other cattle grazing in that area and people need to be advised of the potential risks," Walker said.
He said the discovery of Mycoplasma bovis in Northland was inevitable as farmers bought animals from down the line wherever they could get them cheaper.
Some years ago, he said tuberculosis in cattle was discovered in the Far North because farmers bought animals from outside Northland and now there was further frustration for those trying to resolve another biosecurity issue.
Walker said if more properties in Northland were infected with Mycoplasma bovis or if the disease became endemic, animal management practices would need to be changed.
Replying to Walker's call for the affected farm to be identified, an MPI spokeswoman said
the infected farm owners did not want to be named.
She said since Northland being a small place, people would likely be able to identify the farm in question if MPI disclosed the area.
"To date there hasn't been a single instance of over the fence spread. It's important to note that the detection of new infected properties doesn't mean that the disease is spreading.
"Most of the movements we're tracing are historic and happened before we even knew Mycoplasma bovis was in New Zealand."
According to Dairy NZ, there were 308,587 dairy cows and 1030 herds in Northland - including Rodney District - last year.
Most of the infected beef cattle on the Northland farm will be culled at freezing works.
The farm, as with all other infected properties, was identified through the tracing of animals movements from known infected farms and is under a Restricted Place legal notice under the Biosecurity Act 1993.
MPI has placed the property in quarantine lockdown, restricting the movement of animals and other risk goods on and off the farm.
Northland Rural Support Trust co-ordinator Julie Jonker said her office was working with the affected farm owners to provide a range of assistance they may require at this difficult time.
"We can help them put together their compensation plan but the main thing are issues that cause them additional stress and if they feel people are not hearing what they are saying, we can help them in that regard."
Yonker said she was not surprised that Mycoplasma bovis has been identified in Northland with the testing and tracing regime put in place by MPI around the country which, she said, was working well.
"Eighty per cent of farms under surveillance test negative but it's one of those things that if you want to eradicate, you can't take any chances. People don't realise how big an issue Mycoplasma bovis is," she said.
