A second South Canterbury dairy farm belonging to the Van Leeuwen Dairy Group has tested positive for Mycoplasma bovis.
The Ministry for Primary Industries says the detection isn't unexpected, because of the close proximity to the first infected farm.
The Ministry says it's confident of containing the disease to the group's 16-farm block.
All of the group's farms remain in lock down, to stop the disease spreading to neighbouring animals.
Mycoplasma bovis does not infect humans and presents no food safety risk and there is no concern about consuming milk and milk products, the ministry said.