SAN FRANCISCO (CBS SF) – Within the next two years, McDonald’s USA said they will only buy and use chickens raised without human antibiotics.

It’s part of the company’s new Global Vision for Antimicrobial Stewardship in Food Animals, which was introduced this week. Along with the new policy on sourcing chicken, McDonald’s restaurants in the United States will also offer customers milk jugs of low-fat white milk and fat-free chocolate milk from cows that are not treated with rbST, an artificial growth hormone.

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“McDonald’s believes that any animals that become ill deserve appropriate veterinary care and our suppliers will continue to treat poultry with prescribed antibiotics, and then they will no longer be included in our food supply,” said Marion Gross, senior vice president of McDonald’s North America Supply Chain.

These latest moves build on the company’s 2003 global antibiotics policy. “Our customers want food that they feel great about eating – all the way from the farm to the restaurant – and these moves take a step toward better delivering on those expectations,” said McDonald’s U.S President Mike Andres.

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McDonald’s is the world’s biggest restaurant chain, with roughly 14,000 restaurants in the U.S. and another 22,000 around the world. The phase-out of chickens raised with antibiotics will only affect restaurant in the United States.

McDonald’s has been struggling with a slump in U.S. sales. Revenue fell 2.4 percent last year and net income declined by 15 percent.

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The company said the moves will help them better meet the “changing preferences and expectations of today’s customers.’