A new strain of cattle disease mycoplasma bovis (M-bovis) has been discovered on a mid-Canterbury farm.
The farm is one of four that currently has the disease.
M. bovis eradication programme director Simon Andrew said testing would be stepped up because of the discovery.
"This strain doesn't behave any differently than the strain we have been dealing with, and our existing testing will pick it up, as it has done in this case. It doesn't affect our efforts to eradicate M. bovis from New Zealand."
Andrew said a thorough investigation was under way into historic pathways, which included recorded and unrecorded animal movements dating back to 2018, imported feed and farm machinery, and frozen semen imported prior to the tightening of import health standards for bovine germplasm.
"While considered a very low risk, frozen semen used on the affected property, which had been imported prior to the introduction of the new import health standard, is being looked at.
"Our team is carrying out an investigation on the affected property. At this stage, there is no evidence to suggest that there has been any forward spread on any farms that received cattle from this farm."
The new strain had not been found anywhere else, Andrew said.
"But disease control is all about being cautious, so we will be increasing the summer frequency of our national bulk milk surveillance testing from once a month to every fortnight, as we do over spring."
He said if MPI's investigation into pathways revealed that further action was required, including targeted testing and surveillance on-farm, farmers would be told.
"But at this stage the increased frequency of summer bulk tank milk testing, beef surveillance and tracing animals will serve us well."