OAK BROOK, Ill. - McDonald's Corp has removed chickens raised with antibiotics that are important to human medicine from its U.S. supply chain months ahead of schedule, part of its drive to target increasingly health-conscious consumers.

The fast food company also said it is removing artificial preservatives from Chicken McNuggets and several breakfast items and rolling out new hamburger buns that do not contain high fructose corn syrup.

The changes come as McDonald's competes with other restaurant chains that are overhauling their menus to make them more appealing to consumers seeking healthier options.

McDonald's is "more customer-obsessed than ever before," McDonald's USA President Mike Andres told reporters.

Some health experts have raised concerns that the overuse of antibiotics for poultry may diminish their effectiveness in fighting disease in humans.

The company had previously planned to phase out chickens raised with antibiotics important to human medicine by March 2017. It completed the move earlier due to quicker than expected work by the U.S. Department of Agriculture, which helped to verify that the birds were not given the drugs, said Marion Gross, senior vice president of McDonald's North American supply chain.

Artificial preservatives will be removed from McDonald's pork sausage patties, eggs served on McGriddles sandwiches and scrambled eggs served on breakfast platters, according to the company.