Cows found dead in a Waikato field after a 1080 drop earlier this month ate the poison when they broke into the drop area, it has been confirmed.
The Department of Conservation (DOC) said toxicology tests had confirmed the cows were killed by the toxin.
The Te Kuiti farmers whose eight cattle were killed told RNZ News last week it was possible the cows had escaped into the area where the toxin was dropped.
DOC said initial investigations of the site, communications documents and helicopter flight data indicated the cattle did not have access to 1080 bait on the farmers' paddocks.
In an extraordinary move, DOC is having the pest control operation independently reviewed by the Waikato Regional Council with the aim of reassuring the public.