The farmers whose cows might have been killed by 1080 says it's possible the animals escaped into the area where the poison was dropped.
The Department of Conservation (DOC) is investigating how eight cattle died following a pest control operation over Waikato conservation and private land two weeks ago.
Owners of a dry stock property near Te Kuiti, Paula and Mark Stone, said they were approached by MPI to agree to the 1080 drop on their property - although MPI said it was DOC who approached the farmers - which they did after an official visited them for a meeting.
The couple confirmed that DOC had contacted them two weeks prior to the drop to tell them to move cattle which they did.
They said the bush that was next to the area they moved the cattle from, on the advice of DOC, did not end up receiving an aerial drop, but the area next to the paddock where they moved the cattle to did.
Mr Stone said he would never have moved his cattle to the paddock where they eventually died had he known the area he moved them from would not end up receiving 1080.
He said the communication from DOC and MPI had been poor and there had been "a complete breakdown".
Mrs Stone said the cattle had been let into the bush area in the past where the drop occurred.
"By the bush area there's a track and there's open paddocks in that area and so we do allow them in there, but all winter that gate was secured."
While she said it was not certain the animals had escaped into the operation area, it was a possibility and when DOC visited their property to inspect the dead cattle, they walked the boundary of the paddock and found the fence that had been secured had been damaged.
"But it is likely that they've gone into that area, yes it is very likely."
Mrs Stone said they had seen spillage from the 1080 operation in paddocks on the boundary of the operation, but she confirmed nothing had been found in the actual paddock where the cattle died, although she said it had been 12 days since the drop.
She said she felt very disappointed, misled and hurt about the situation.
Incident fuels 'abusive' anti-1080 approach
DOC Operations Director David Speirs said staff had been to the site and all the evidence pointed to the animals escaping on to pasture in the drop zone.
"The gate in question was secured to a post by a piece of wire around its middle, and it's rotated around that piece of wire. The gate wasn't well secured at all."
No bait was found in the paddock where the cows were found dead, he said.
A 500kg animal would have to eat 22 or 23 baits to get a toxic dose, but it wasn't impossible a cow would eat that much. The drop rate is 300 baits per hectare.
GPS-based data showing where the helicopter flew and the follow-up on the ground confirmed the baits were dropped where they were supposed to go.
Third parties make use of these kind of incidents to fuel opposition to 1080, he said.
"The tragedy of this is ... it distracts from the real message, which is that we're trying to save New Zealand's biodiversity.
"We will lose the battle if we don't use tools like 1080.
"The other thing it does is it fuels this awful, very abusive approach that 1080 protesters and anti-1080 people are taking towards my staff, towards the department and that's just incredibly inappropriate."
Mr Speirs said DOC staff visit private properties before a 1080 drop to check landowner agrees to it, but it is the farmers' responsibility to secure boundaries.
"It's a partnership and if both parties do what they say they will do the operation goes flawlessly."
"We certainly don't force landowners to participate. If they choose not to have their land involved then we work around that.
"In this case, the Stones agreed that that parcel of land would be involved in the 1080 operation."