One of two Waimate district farms, which were placed under restrictions this month, has tested positive for the cattle disease mycoplasma bovis.
Testing is ongoing on the second property, while a third property has been placed under restrictions for the time being.
All three farms are in the same district and a couple of them neighbour Van Leeuwen Dairy Group properties, says Ministry for Primary Industries (MPI) incident controller David Yard.
The disease was detected at two Van Leeuwen Dairy Group farms in August.
"We still have a lot of work to do ascertaining the source of infection at the confirmed infected property and building a picture of animal movements between all three farms and possible other farms," Mr Yard said.
MPI is assuring farmers that if mycoplasma bovis is present, it will be found.
The disease was first detected in cattle on a South Canterbury farm on July 22.
The cattle disease is spread through close contact between animals and through the direct movement of cattle between properties.