The Veterinary Association has publicly attacked a vet for suggesting the Fonterra botulism contamination may have come from cow's milk.
Frank Rowson is a qualified vet who has worked in New Zealand and around the world.
He believes the feeding of genetically engineered soy bean meal to cows may have been a factor in botulism spores getting into Fonterra's product.
Fonterra maintains the botulism spores came from a dirty pipe at one of its plants.
After repeatedly declining to discuss anything about botulism in New Zealand agriculture and saying it didn't have any information on it, the Veterinary Association broke its silence on Thursday to attack Mr Rowson.
It issued a statement saying his comments were speculation and unhelpful.
It says Mr Rowson is not currently registered as a vet and he doesn't represent the profession.
Mr Rowson had never claimed that he did.
The Veterinary Association says it is working with the Ministry for Primary Industries on the ministry's investigations and any farmers concerned about botulism should contact their vet.