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 realise 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.

"No animals have left the property since 20 July. However it is understood that before this, some animals were moved to a number of other farms," Gwyn said.

"MPI is contacting those properties and is testing animals with urgency."

Mycloplasma bovis was first confirmed in New Zealand on July 22.

It is found in cattle globally, including in Australia, and can cause udder infection, abortion, pneumonia and arthritis. It poses no risk to humans or food safety and there is no concern about consuming milk products.