A third South Island farm is suspected to have the cattle disease mycoplasma bovis and it may have sent animals to other properties.
The farm, in the Oamaru area, has a direct connection with one of the infected Van Leeuwen Dairy Group farms, the Ministry for Primary Industries says.
It received some animals from the Van Leeuwen farms before officials realised the disease, which spreads between cows in close contact, was in the country.
Blood test results show some animals were infected.
The ministry's Geoff Gwyn says the property is now under restrictions, which include controlling the movement of animals and other risk materials off the farm.
