Test results across five farms linked to the laying farm came back negative for bird flu. Photo: AFP
The Ministry for Primary Industries expects it could take months to repopulate an Otago poultry farm that tested positive for bird flu.
About 200,000 birds were culled at Mainland Poultry's Hillgrove site late last year after the N6 strain was found there.
The property remained under biosecurity control while cleaning and disinfecting was underway.
The ministry's chief veterinary officer Dr Mary van Andel said they had been working closely with Mainland Poultry to carefully plan the next steps as they had been "really fortunate" that it was contained to one property and now the aim was to remove all traces from the farm.
Cleaning was expected to carry on for weeks as every trace of dirt and chicken litter needed to be removed and disposed of in a biosecure way, she said.
"Those sheds need to be cleaned and disinfected and then there would be a waiting period for the sheds.
"But as you can imagine, the waiting period for a range or a field is quite a lot longer than it is for something that you can disinfect and so we are talking more about in the order of months for that than weeks."
They were learning from international experience about the the best ways to kill the virus and prevent it from persisting in areas like free range fields.
"This involves fallowing those fields and there are measures that can be taken to change the PH of those ranges by spreading things like lime or those kinds of things.
"So quite an involved process, quite intensive ... but not impossible."
Last month, test results across five farms linked to the laying farm came back negative for bird flu.
"We've continued to monitor, keep a really close eye on these farms and there are no signs of disease anywhere else," van Andel said.
"So that significant number of tests as well as no clinical signs, that really gives us confidence that the virus was contained to that single site."
The spread had been contained after fast reporting from the farmer and how they had been able to work together, but she said public reporting remained "absolutely key" to early detection.
She encouraged anyone who saw three or more sick or dead birds in a group to report it immediately to the exotic pest and disease hotline on 0800 809 966.
The ministry received 27 notifications about dead or sick birds between Christmas Eve and 8 January, but no bird flu was detected.
They investigated all reports of multiple bird fatailites - receiving many of them each year. The main diseases they wanted to exclude were are HPAI and Newcastle Disease, van Andel said.
"Large numbers of bird deaths are not uncommon and, in many cases, botulism or toxic algal bloom are found to be the cause. Other causes of seabird deaths we have investigated indicate that starvation and storm-associated events are possible causes of deaths in these species."
They were also continuing to work with different trade markets about what they needed to provide to show that bird flu was contained.
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