Farmers are raising concerns and questions about new Fonterra guidelines which suggest farmers should limit the amount of palm kernel expeller (PKE) they feed to stock.
This week Fonterra released guidelines suggesting cows should be limited to three kilograms of PKE per day.
Palm kernel expeller is used widely by dairy farmers as a supplementary feed, especially in times of drought or excessive rain which hinders the growth of other crops.
The dairy co-operative maintains they are guidelines, however, it has told farmers it is looking to develop a method to test milk for indications of high PKE use - ready to be used next year.
South Waikato veterinarian and dairy farmer Ian Scott said it had come as a surprise and farmers were wondering where the guidelines had come from.
He said there had been little explanation or even science reasoning behind the 3kg amount.
"There has been no discussion, consultation, attempts to come out and contact the people who are most concerned and who this is most going to affect, which are the farmers themselves.
"It is my understanding that the Shareholders Council, which are our representatives on Fonterra, had not even had the issue raised or brought in front of those members.
"So to simply send us a letter saying 'this is what we're going to tell you are the guidelines' and they may well soon be a condition of your supply, I think is fairly blunt, and wouldn't be the way I'd go about doing business with my clients or shareholders."
He said farmers were pretty aggrieved.
"At the moment we're suffering extreme weather conditions. People in Southland are in bad trouble with just extreme wet. They're having to feed large amounts of supplementary feed to their cows, not only to try to keep them milking, but also from an animal welfare point of view."
Mr Scott said farmers were concerned PKE limits would be part of conditions of supply.