The Ministry for Primary Industries (MPI) has confirmed a cattle disease never before seen in New Zealand has been detected in a herd on a South Canterbury farm.
Mycoplasma bovis does not infect humans or pose a food safety risk, but can seriously affect cattle, with side-effects including udder infection, pneumonia and arthritis.
Out of a herd of 150 cows, 14 have tested positive for the disease, which requires close contact between cattle in order to spread, but can also infect milking equipment.
MPI response director Geoff Gwyn said the ministry was not sure how the disease entered the country.
"It is serious from a production and animal welfare perspective.
"We're carrying out tracing activities and movements of any risk goods into the farm concerned, but at this stage I can't speculate.
He said it may never be known how the disease arrived in New Zealand, and the focus was now on containing the spread of the disease and testing the remainder of the herd.