Legal action won't be taken over the deaths of almost 200,000 chickens in a commercial barn in 2019, the Ministry for Primary Industries (MPI) has confirmed.
Between 180,000 and 190,000 chickens died at the west Auckland farm, which supplied Tegel, after the air supply was cut to the barns by a power outage lasting 48 minutes - causing them to overheat or suffocate.
MPI earlier this year had asked Crown lawyers for advice on the matter but on Wednesday confirmed it wouldn't be pursuing prosecution.
"The person in charge of the animals took steps to maintain that equipment and Crown Solicitor advised this provided a defence to potential charges under the Animal Welfare Act," MPI compliance director Gary Orr said.
As a result, Orr said the incident didn't meet the threshold for prosecution.
The matter required careful consideration - given the technical evidence and number of chickens involved, he said.
"The systems on the farm have subsequently been upgraded to ensure this does not occur again."
Jessica Chambers, from animal welfare group SAFE, said the investigation should have been a priority.
"Considering 180,000 birds lost their lives, MPI's decision not to prosecute is not only unacceptable, [but] it demonstrates a complete lack of regard for their obligations to those animals," said Chambers, SAFE's campaigns manager.
"It's time to walk the talk by appointing a fully resourced Commissioner for Animals with the power and will to regulate and enforce animal welfare laws."