KEY POINTS:
For years the claims have circulated in the scientific community but gone largely un-noticed by the public. The shocking suggestion is that the milk we're drinking could be contributing to serious disease in those consuming it.
Now that the issue has exploded into public consciousness this week, the question being raised is why the people providing our milk have not acted when a solution seems so simple.
"The opportunity still exists, but what a great pity we are not so much further down the track than what we are," says Professor Keith Woodford, whose new book Devil in the Milk has sparked the fierce debate.
The book gives a blunt assessment of the attitude of Fonterra, the world's largest dairy trader, and suggests it failed to react to concerns because of politics and the message it might send to its massive foreign customer base.
The issue is simply one of two types of milk produced by cows in this country, A1 and A2.
Studies have linked a protein in A1 to diseases like diabetes and heart disease, while A2 is touted as being a safe alternative.
Most milk bought off the shelf in New Zealand is a mix of A1 and A2, but critics of A1 want a shift in the insemination of dairy cows to produce solely A2.
A natural shift is already occurring towards a greater prevalence of A2 in the industry "but it's like driving down the highway in first gear - we are going to take an awful long time to get there", Woodford says.
Fonterra refused requests by the Weekend Herald for comment on the claims in Woodford's book, and the dairy giant has taken the position that the science does not back up the claims. Woodford, a respected Lincoln University scientist, says Fonterra has not only convinced itself A1 is safe, it has convinced the industry overseas in a series of papers presented at an international dairy forum calling it a "non-issue".
But more than 100 peer-reviewed papers say otherwise, Woodford says.
"The words I tend to use are that the evidence is extremely compelling. People can debate the meaning of proof [but] science really works on the basis that very seldom do you have absolute proof. But I have no doubt the evidence is very strong.
"Wherever we have high A1 beta caseine, we have high levels of diabetes, and we also have high levels of heart disease, and that evidence passes the statistical tests.
"There are only going to be some people probably that are susceptible, but we don't necessarily know which people those are going to be. And the most important time is going to be when you are young."
Frank Brenmuhl, chairman of the Dairy Farmers of New Zealand, says the industry has not acted because it is faced with a hypothesis and not proven science.
"A lot of people have suggested serious links [to health problems] but people who don't drink milk are less healthy than those that do."
Woodford says dairy herds could be converted to A2 without a great amount of cost. The companies providing bull semen to farmers to inseminate their cows could simply make the solely A2 semen available.
But it would be seen by the industry as a backdown "having told all these other people that A2 was a non-issue".
Brenmuhl agrees there is little financial cost in a large-scale conversion to A2, but says it may have serious consequences down the track.
"We would be reducing the genetic base of the herd quite substantially. You are bringing the gene pools really close. We don't know what the strengths and weaknesses of that are.
"We would only do it if there's a very good reason, and at the moment, we don't have that."
To consumers shaken by the controversy this week, Woodford insists people should not stop drinking milk.
"All I can say to people really is 'what do I do?' And if I can get A2 milk, I drink A2 milk. If I can't get A2 milk, I still end up consuming some A1 milk in a range of products, on my Weetbix in the morning, etc. But I'm just cautious as to how much of it I consume."
The New Zealand Food Safety Authority, another target of Woodford in his book, goes much further in its advice to consumers, saying there is insufficient evidence that A1 milk is unsafe, or that A2 is any safer.
The authority said this week it was concerned that "unsubstantiated claims do nothing more than scare some people away from a safe, nutritious and beneficial food".
Woodford argues that bodies like the Food Safety Authority are being influenced by the fact that the dairy industry underpins the New Zealand economy
"Therefore we do things, and we see the food safety people doing things, which are all about protecting the New Zealand industry. And that's a slippery path. That just puts you in the same category as all the tobacco people. People are shocked when you say that, but that's what it is."
He admits members of his family have previously owned shares in A2 Corporation, which pushes A2 milk, after a colleague got him interested in the concept. However, they sold the shares before the book was published to avoid any image of him being viewed as partisan.
"For me professionally, it would [have] been easier to have walked away from this whole issue. Even if this book is a huge seller ... I'll end up losing a huge amount, [having earned] less an hour than what I can earn in just about anything else.
"You wouldn't write a book like this if your aim was to make money. You write a book like this because you believe there is something important that needs to be said."
He said public pressure was needed to get the dairy industry producing the safest type of milk for sale.
"If you ask me what's the solution to do tomorrow - that's a little bit tricky," Woodford says. "But next time you go to the shop [and buy A2 milk] and enough people start doing it, [then] we have it in a whole range of shops, then very soon we can be in the situation where people don't have to make those difficult decisions."
A Big Business
* In 2005/06, dairy companies processed 14.7 billion litres of milk and 1.27 billion kg of milk solids.
* The average dairy company total payout (per kilogram of milk solids) received by dairy farmers in 2005-2006 was $4.10 but the forecast for 2007-2008 is $6.40
* The total cow population is 3.832 million in 11,883 herds.
* The vast majority of dairy herds (81 per cent) are located in the North Island, with the greatest concentration (32 per cent) in the South Auckland region. Taranaki, with 16 per cent of dairy herds, is the next most heavily populated region. South Island dairy herds account for 19 per cent of the national total, but have 28.6 per cent of the cows.
* Three dairy breeds (Holstein-Friesian, Jersey, and to a lesser extent, Ayrshire) dominate with Holstein-Friesian being 47 per cent of the national herd
- Statistics: LIC
