The U.S. Agriculture Department has approved a slaughter technique considered more humane and pain-free called controlled-atmosphere killing that replaces oxygen with argon or nitrogen gas to kill the animals.

Currently most chickens are slaughtered when their throats are slit while hanging upside down from a moving conveyor line pulled through a vat of electrically charged scalding water.

People for the Ethical Treatment of Animals, an animal rights group, had planned to introduce a proposal calling for the study at McDonald's stockholders meeting. McDonald's is the world's No. 2 buyer of chicken.

"We have been studying animal welfare issues since the middle 1990s," Bob Langert, McDonald's senior director of social responsibility told the Chicago Tribune. He said the company's animal welfare council recommended the alternative slaughter method be studied.