Oregon dairy farmers reaffirmed their intention to keep a bovine growth hormone off their cheese plate, much to the chagrin of the drug’s manufacturer, bioengineering giant Monsanto.

On Feb. 28, farmers in the Tillamook County Creamery Association, the second-largest producer of natural chunk cheese in the United States, voted 83 to 43 to uphold a ban on the use of Posilac, an artificial growth hormone also known as rBST and rBGH. The drug, approved by the U.S. Food and Drug Administration in 1993, boosts milk production by 5 to 15 percent.

Last May, the association’s board decided to ban the use of Posilac, prompted by growing consumer concerns over its effects on the health of cows, the increase of antibiotic-resistant bacteria in milk, and the possibility that the hormone may cause cancer in humans.

Monsanto reacted quickly, sending officials to Oregon to ask the association to drop the ban. According to Christie Lincoln, an association spokesperson, in January, 16 farmers petitioned to amend the association’s bylaws to prohibit it from banning FDA-approved drugs like Posilac.

Some farmers suggest that the biotech giant helped draft the proposed amendment. "Their lawyer walked in with the bylaw change," says Richard Heathershaw, who stopped using the hormone on his 200 cows more than two years ago. But the February vote rejected the amendment, upholding the board’s original Posilac ban, which takes effect April 1.

"We hope that in time Tillamook producers will reconsider this policy," Monsanto Co. wrote in a response. According to Jennifer Garrett, public affairs director for Monsanto’s dairy business, one-third of the nation’s nine million dairy cows receive Posilac.

In recent years, Monsanto has sued dairies, such as the Oakhurst Dairy in Maine, for labeling their products "rBGH-free." The company claims there is no discernible difference in the milk. Tillamook, however, is not planning to change its labels.