One new property has tested positive for the cattle disease mycoplasma bovis.
The property is owned by the Van Leeuwen Dairy Group, which has 16 farms in the South Canterbury and North Otago region.
The latest case brings the total to seven infected properties in the outbreak to date.
Five of the infected farms are owned by the Van Leeuwen Dairy Group, one is in North Otago, and the seventh is a lifestyle block in North Canterbury.
The Ministry for Primary Industries said the latest infected farm was already under a restricted notice.
"We've said all along that we fully expected the possibility for further farms within this enterprise testing positive," response incident controller Stephen Bell said.
"The nature of this disease is that it spreads between animals that are in close, repeated and prolonged contact."
The latest detection showed the ministry's protocol of testing herds up to three times was working, he said.
"It has meant there has been a long period of disruption and uncertainty for farms that are being tested but we have to be absolutely thorough in diagnosing positive and negative farms."
Over 26,000 of a planned 39,000 tests have now been completed by the ministry's laboratory in Upper Hutt.
"As our picture grows and as more and more test results come back, the greater our confidence that the disease is being well contained on the known infected properties," Mr Bell said.
If samples beyond the infected properties continued to test negative for the disease, the ministry would consider assessing whether the disease could be eradicated.