"The eye and right side of the head were grossly swollen; there was brown discharge from the eye, extensive scar tissue on the cornea, and a bacterial infection," MAF said.
It was likely the cow would have been in considerable pain and suffering from the tumour, the vet said.
Komene admitted to a MAF animal welfare investigator that he knew the cow had a swollen eye months earlier and he had tried to treat it himself.
He did not seek veterinarian advice and knew it had got worse.
MAF regional operations manager Ross Thurston said not treating eye cancer was unacceptable, especially since treatment could easily be sought.
"Cancer eye is treatable and recovery rates are near on 90 per cent. There is no excuse for animals to be unnecessarily suffering because of it and we take reports very seriously."