McDonald's (MCD) says sales of its Quarter Pounder burger are up 30% since replacing frozen beef patties with fresh ones.

"We sold 40 million more Quarter Pounder burgers nationally in the first quarter of the year compared to the quarter in 2018," Marion Gross, McDonald's senior vice president of supply chain management, told USA Today.

The change comes as the fast-food giant's competition has been offering fresher, healthier hamburgers.

Ethical concerns have also prompted McDonald's to reduce the antibiotics it uses in its beef. The National Resources Defense Council in 2018 gave McDonald's an F grade on its antibiotic policies.

McDonald's rival, Wendy's, claims that it has always used fresh beef. Wendy's criticized McDonald's last year on Twitter, by noting that not all of McDonald's burgers use fresh beef. The Big Mac, Hamburger and Cheeseburger on McDonald's menu still use frozen beef patties.

Burgeoning burger chain Shake Shack also uses all-fresh, antibiotic-free beef for its burgers.

The burger industry is currently undergoing a period of innovation, as climate-conscious consumers are interested in meatless burgers.

Fast food giant Burger King, for example, has introduced the Impossible Whopper burger, which is completely plant-based. In Europe, McDonald's also offers a meatless burger.

McDonald's is the world's largest hamburger chain selling more than 75 burgers per second.