Bovine tuberculosis has been found in Golden Bay for the first time in a decade.
Animal health agency Ospri, which manages the TB-free programme, said the infection was detected during routine testing in two percent of a medium-sized herd in Collingwood.
Ospri national disease manager Kevin Crews said the agency had restricted animals from moving on or off the property.
The agency suspected the infection was brought in by an animal from outside the area, he said.
Tasman district's TB-free committee said nine times out of 10, a TB infection was not the farmer's fault.
TB is spread mainly by possums, and can cause serious production losses and animal welfare issues.
Farmers and agricultural authorities have been battling it since the 1950s.
Last year, a case was confirmed in a Waikato dairy herd.