News that New Zealand cows are being fed genetically modified soy and cottonseed meal has come as a shock to many consumers who imagined our dairy cows were happily chomping away on an exclusive diet of lush green grass.
It will be even more of a shock, I suspect, to overseas consumers who have seen advertisements claiming our cows are fed "lush green grass, year round", and who assume that dairy cows reared in clean, green New Zealand would not be fed genetically modified feed.
But it turns out our so-called "grass-fed" cows are being fed more supplementary feed from a variety of sources.
As dairying has become ever more intensive, with more cows per hectare, the industry claims that cows need to be fed more than just grass to produce the large quantities of milk the industry demands.
And so the industry has been quietly importing palm kernel - a byproduct of palm oil.
Last year we imported 1.5 million tonnes of palm kernel from Malaysia, Indonesia, Papua New Guinea and Singapore to feed to dairy cows.
These imports are helping to destroy the tropical rain forests in Southeast Asia, and the habitat of endangered species such as the orang-utan.
They are also helping to destroy the grain industry in New Zealand. Many grain farmers who could supply alternative feed for dairy cattle have been unable to compete with cheap palm kernel imports and have gone out of business.
This is bad enough, but now it turns out that the dairy industry has also been quietly importing substantial quantities of soy and cottonseed meal, which is almost certainly genetically engineered, to feed to our dairy cows. In the last few years, several hundred thousand tonnes of soybean and cottonseed meal have been imported, mostly from Argentina (where almost all soybean crops are genetically engineered), Indonesia and Australia (where most cotton seed is genetically engineered).
According to the farming newspaper Straight Furrow, an entire shipment of genetically engineered cottonseed landed in Timaru recently, destined for dairy herds in the South Island.
There is nothing illegal about this, as genetically engineered feed can be freely imported into New Zealand. It doesn't even have to be segregated from other non-GM feed or declared on a label because it is not for human consumption, and our food safety agency claims there is no difference between GM-fed animals and animals that are not given GM feed.
It makes the further claim that when animals are fed GM feed, the genetically modified protein or DNA from the feed cannot be detected in milk.
This claim is contested, however, and is the subject of scientific dispute.
That's why many European supermarkets such as Sainsbury's, Marks and Spencer's and Carrefour, stipulate that any milk or meat they sell must come from animals that have not been fed genetically modified feed or ingredients.
In New Zealand, our Commerce Commission has accepted evidence from Professor Jack Heinemann that animals fed on GM feed are different from animals that are fed on non-GM feed. Surely, therefore, consumers have a right to know whether milk on sale in the supermarket comes from cows that have been fed GM stock feed, so they can choose whether or not they want to buy this milk.
I am sure many consumers would want to avoid drinking milk from cows that have been fed GM feed.
But since there is nothing on a label to alert consumers, the only way they can be sure they are not drinking milk from GM fed cows is by buying organic milk.
I am certain, too, that many overseas consumers - and supermarkets - would not want to buy milk from GM fed cows, and I wonder whether Fonterra realises how damaging it would to its brand if overseas consumers find out that our cows are routinely fed GM feed.
This raises the question, why is Fonterra allowing imported GM stock feed to be fed to our dairy cows?
Or has it not carried out consumer research on GM food, and does it under-estimate the strength of consumer concern about genetically modified food?
Now the news is out, Fonterra would be strongly advised to require dairy farmers to switch to non-GM animal feed. Otherwise it risks a consumer backlash, here and overseas, against its brand.
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Sue Kedgley is a safe food campaigner and former Green MP.