(Host) The region's largest dairy cooperative wants to phase out use of a controversial growth hormone that's used to boost milk production.

The Agri-Mark dairy co-op says it's following the lead of its customers - who have rejected milk from hormone-treated cows.

VPR's John Dillon reports:

(Dillon) Agri-Mark has told its members that starting in August it will no longer accept milk in New England from cows injected with the hormone. The product is made by the Monsanto Corporation and it's called bovine somatatropin, or BST.

Spokesman Doug DiMento says the issue has been under discussion for 15 years - since the hormone was first introduced in the early 1990s.

(DiMento) "But during the last few months we've told our members that it seems like the market for milk from farms using synthetic BST is diminishing and we won't have any markets for that milk over the next several months. So we're trying to take steps to preserve markets for our farmers."

(Dillon) BST can boost milk production in cows by around 15 percent.

But it was controversial from the start. The Food and Drug Administration said it was safe. And many farmers viewed it as simply another management tool. But consumer organizations worried about the hormone's impact on cows and on humans.

In response, organic milk companies and many conventional dairies began marketing their product as hormone free.

And last year, retail giant Wal-Mart announced that it would no longer sell milk under its own label from hormone-treated cows.

DiMento says the market pressure has now gone beyond Wal-Mart.

(DiMento) "Now some of our bulk cheese customers are requesting this. Some of our milk powder customers for our milk powders are requesting this. We have been segregating milk where we can over the last several years. But we reached the point now where we had to make this decision. The board decided to make the decision and move forward."

(Dillon) The debate within the dairy co-op focused on whether the organization should ban a legal product that can help farmers boost production.

(Ainsworth) "And it was with great trepidation that the board finally did make that choice."

(Dillon) David Ainsworth is a dairy farmer and Republican representative from South Royalton. He's an Agri-Mark member, and milks a small herd of Holsteins and Brown Swiss cows. He doesn't use the hormone, but he understands why some farmers would choose the technology.

(Ainsworth) "I didn't have any problem with the science behind it. Cows naturally produce the growth hormone themselves. That's why the high producing cows do better.... This was just supplementing it on animals that were not producing it as high. It had no effect on the quality of the finished product."

(Dillon) Agri-Mark has about 1,300 members in the region, and 360 in Vermont.

The ban on BST will affect milk processed in Agri-Mark's New England plants. A plant in New York will still accept milk from cows injected with the synthetic hormone.

But Ainsworth said farmers will have to pay an extra charge to truck their milk to the New York plant.

For VPR News, I'm John Dillon in Montpelier.