CHICAGO (Reuters) - McDonald’s Corp will require suppliers to follow new standards for raising and slaughtering chickens served in its restaurants, the company said on Friday, the latest changes affecting popular menu items like McNuggets.

FILE PHOTO: The logo of a McDonald's Corp restaurant is seen in Los Angeles, California, U.S. October 24, 2017. REUTERS/Lucy Nicholson

Animal activists said the mandates fall short of commitments made by other restaurants, such as Burger King and sandwich chain Subway, and failed to address their primary concern about chicken production: birds bred to grow quickly to large sizes.

Under McDonald’s updated guidelines, suppliers such as Tyson Foods Inc and Cargill Inc [CARG.UL] must comply by 2024 with rules dictating the amount and brightness of light in chicken houses, provide birds with access to perches that promote natural behavior, and take other steps to improve animal welfare.

The world’s largest restaurant chain by revenue also pledged to conduct trials with suppliers to measure the wellbeing of different chicken breeds.

“I think it’s one of the most comprehensive programs that I’ve seen for chickens,” said livestock researcher Temple Grandin, who pioneered humane slaughterhouse practices and works with McDonald’s.

The treatment of animals in the food chain has become increasingly important to some consumers in recent years as animal welfare groups have released undercover videos showing abuse at U.S. facilities, including those associated with Tyson.

McDonald’s requirements are the latest changes to affect its menu that address concerns about animal and human health. It previously stopped buying chicken meat for U.S. restaurants from birds raised with antibiotics deemed important to human health and said it would shift to using cage-free eggs in the U.S and Canada.

Such moves generally raise costs for producers.

McDonald’s, which has been working to boost flagging traffic at its U.S. restaurants, said it will not raise menu prices as a result of its new standards.

“While this might not be a direct impact on sales at McDonald’s, it might help certain segments of our customer base make purchasing decisions that they might not have otherwise made,” Bruce Feinberg, a senior director for McDonald’s, said about the requirements.

Tyson and Cargill supported McDonald’s moves.

However, animal welfare groups said the chain failed by not committing to buying meat from breeds that grow slowly enough to protect chickens’ health. Birds bred to grow more quickly can suffer organ failure and struggle to walk because they become too heavy, they said.

“McDonald’s at this point is allowing the industry to continue in this inhumane direction,” said Josh Balk, a vice president for The Humane Society of the United States.