Dairy farmers whose herds are culled through the Mycoplasma bovis eradication programme could be back in business within months, but for most it will take years to rebuild their herds to full strength, DairyNZ's Andrew Reid said.
The 39 infected properties have been earmarked for "depopulation", which means all their stock will be killed.
Reid, who is DairyNZ's general manager for the farmer-funded body's team of advisers, said the process of restoring herds will depend on stock availability and the price farmers are prepared to pay.
"It's no easy feat by any means, given the time of year that some of this culling is taking place," he said.
Farmers sourcing new herds will also have to understand the history the herd, including getting M. bovis records of tests from the autumn, which should be part of sale agreements.
"Herds get bought and sold each year," he said. "In the context of the greater industry it is manageable, but the laws of supply and demand, when there are not many herds for sale, will drive the market - not just stock prices but the availability as well," he said.
There is a stand-down period of 60 days for infected farms after they have been depopulated, during which time farms are cleaned and disinfected.
Getting herds back to their former size and quality will take time for some.
"In many circumstances, generations of breeding programmes have been wiped out through the culling programme. So as well as the production implications there is the emotional toll that farmers are going through," he said. "Getting a herd of the same quality could take a considerable period of time."
Reid said getting rid of existing herds will be testing for farmers.
"Seeing good quality stock loaded onto a truck will be a pretty traumatic experience," he said.
Cows can be milked at 2 years of age, and the typical lifespan of a dairy cow varies from 6 to 10 years.
Rabobank dairy analyst Emma Higgins said the cull could see "regionalised inflation" for replacement stock in hard-hit infected areas.
For most farmers, the season officially ends today. It will be two months before new season production resumes.
Prime Minister Jacinda Ardern this week announced that the Government and farming sector leaders had agreed to try to eradicate the cattle disease Mycoplasma bovis from New Zealand to protect the national herd and the long-term productivity of the farming sector. She said the country had "one shot" at getting rid of the disease, which causes painful, untreatable illness in cattle.
The decision to eradicate was taken collectively by Government and farming sector bodies after months of intense modelling and analysis.