Starbucks Coffee Co. (SBUX) is ending its use of milk products that contain an artificial growth hormone, starting in much of the West and New England.

Less than a month after announcing that the chain would stop selling items with trans fats in half its U.S. stores, Starbucks said Tuesday it had begun buying only milk products without bovine growth hormone in those areas.

Starbucks has not raised prices and is working with suppliers on the cost of milk, half and half, whipping cream and eggnog, spokeswoman Sanja Gould told the Seattle Post-Intelligencer.

Starbucks has 5,668 stores in the United States, but the number affected by the change was not immediately available. It covers company-owned Starbucks outlets in Washington, Oregon, Idaho, Alaska, Montana, Northern California and New England.

Earlier this month Starbucks announced plans to stop selling food containing trans fats at half the company's U.S. outlets.

For more than a decade, some advocacy groups have asserted that there has not been enough research on the effects in humans of milk products from cows that were given the hormone, which is administered to dairy cattle during the middle phase of lactation to boost milk production.

"We think it's good news, and we are happy to hear it," said Patty Lovera, assistant director of Food and Water Watch in Washington, D.C., after learning of the Starbucks move.

Large-scale dairy operators there is no scientific evidence to suggest any effect on humans from the recombinant bovine growth hormone, (rBGH), which is marketed as Posilac by Monsanto Co. of St. Louis, which obtained approval from the Food and Drug Administration for commercial sales beginning in early 1994.

"Growth hormones only work on their own kind. A lot of people don't understand that," said Blair Thompson, a spokesman for the Washington Dairy Products Commission.

Starbucks likely will wind up boosting prices because the hormone is now so widely used, Thompson said.

"Unless they are willing to absorb a higher cost and take a smaller profit, they will have to pass it on to the consumer," Thompson said. "They will have to pay more to get the product."

Gould said Starbucks had planned to announce the switch after it was complete nationwide but began answering questions about it Tuesday following a report by the Reuters news agency.

As of this month, 37 percent of dairy products Starbucks buys for U.S. outlets are bovine hormone-free, compared with 27 percent last month. Gould did not give a timetable for reaching 100 percent.

"We have strict standards to ensure our products have high quality, and we want to meet our customers' needs and preferences," Gould said. "We are working with suppliers and working with ways to have rBGH-free milk."