Another 1000 cattle on a newly identifed infected Waimate property will be culled on top of the 4000 cattle already scheduled for destruction because of Mycoplasma bovis.
The latest farm to test positive is one of two in the Waimate district placed under restrictions last week.
Testing was ongoing on the second property, while a further farm in the area was yesterday placed under the same controls while further testing was done to determine if it was infected.
All three farms were in the same district and several neighboured Van Leeuwen Dairy Group properties, the Ministry for Primary Industries' response incident controller David Yard said.
The culling of about 4000 dairy cattle from five Van Leeuwen Dairy Group properties has been signalled following an outbreak of the bacterial disease which could cause mastitis, abortion, pneumonia and arthritis.
Mr Yard said it had been hoped to have the original 4,000 animals culled before the end of the year.
"However as the number of infected properties increases, as with this latest detection, any final completion date will be moved out."
There was still a lot of work to be done to ascertain the source of infection at the confirmed infected property and building a picture of animal movements between all three farms and possible other farms, he said.
Mycoplasma bovis was spread through close contact between animals and through the direct movement of cattle between properties.
MPI's response team was now planning for how the new infected property would be managed and continuing testing of samples from the two other properties.
It was a very stressful time for everyone involved and MPI was working hard to locate and contain the disease, he said.
Farmers with any concerns could call the Mycoplasma bovis farmer support line on 027 4449380 or their local Rural Support Trust on 0800 787 254 (0800 RURAL HELP).