But after taking advice from the Crown Solicitor, MPI did not pursue prosecution – a move that shocked animal rights advocates.
After obtaining the investigation summary under the Official Information Act, the Herald can reveal the reasons behind that decision.
The mass chicken deaths were a result of the "uncontrolled ambient temperature and humidity in the sheds rising to fatal levels owing to the failure in the electrical switch preventing the backup generator to start", the summary said.
"The power failure also prevented the alarm sounding, which meant the manager was unaware of the issue until it was too late."
Email correspondence proved the manager had not been advised by the security company behind the alarm system that he needed an Uninterrupted Power Source (UPS) in order for a notification to be sent to his phone after the loss of power.
The investigation found the farm manager "took all reasonable steps to ensure animal welfare and safety by relying on experts to make sure his systems were capable of alerting him to faults".
The report recommended MPI did not charge the farm manager because he would have "a reasonable defence ... in that he took all reasonable steps to ensure animal welfare".
It also recommended MPI did not charge the owner of the chickens, and there was "insufficient evidence" to charge the contracted grower, or its directors.
What went wrong
There was a power cut at the farm sheds at around 2am on Friday, November 29, 2019.
The grower was woken up by the alarm app on his phone and a text from the monitoring company.
On this occasion, the generator started correctly, and the mains power was restored to the shed, the summary said. The manager went to the sheds and checked the operation of the shed.
But around an hour later there was another power cut at the sheds.
This time the generator did not start due to a fault with the relay switch and there was no power to the sheds – and therefore no alarm was sent.
Alarm systems were installed on the Helensville farm in 2013 and 2014 to notify of a power failure.
They were installed and maintained by a security company and monitored by an external alarm-monitoring company.
The system used a router, rather than a landline, to send out an alarm message to the monitoring company and then to send an alert to the app on the manager's phone.
But for an alarm to be sent through either pathway, the router required power such as through a UPS, the summary said.
During an interview with the farm manager following the chickens' deaths, he claimed he had never been advised by the security company regarding the requirement to have any UPS if they had alarms being sent through a router.
"A search of relevant emails cloned during the search warrant phase of the investigation regarding the setup of the alarm system found no mention or information regarding having any UPS," the summary said.
A standard animal welfare audit at the farm, conducted around two months before the deaths, found no problems with generators, alarms, systems and animal welfare.
"Turning off both the mains power and generator together was not covered in the audit, however the generator was tested regularly and these tests were documented," the summary said.
"The main factor to consider was whether the alarm system met the standards as per the Animal Welfare Meat Chickens Code of Welfare (October 1, 2018) and whether it was reasonable for the manager not to have identified the issue with the router.
"The recommendation was not to charge the manager because he would have a reasonable defence ... in that he took all reasonable steps to ensure animal welfare and safety by relying on experts to make sure his systems were capable of alerting him to faults."
In July, MPI director of compliance Gary Orr said systems on the farm were upgraded to ensure a mass death event would not occur again.
