The Ministry for Primary Industries has defended a decision to send 3000 dead calves to a landfill near Winton.
The Clutha-Southland MP, National's Hamish Walker, asked Mr O'Connor when he was made aware of the ministry sending the calves to landfill.
Mr Walker asked whether an assurance could be given that no more calves would be sent to that landfill.
Mr Gwyn said there would be calves that would have to be disposed of, but they would only go to accredited landfills.
"This is, and I must stress, the absolute last resort - so I can give you that guarantee, what I can't give you is a guarantee we won't do it again."