Burger King Corp. pledged Wednesday to begin buying eggs only from farms that don't cage their hens, a step beyond its fast-food competitors' efforts to push for better treatment of food-producing animals.

The chain also said it will begin buying pork only from producers that don't use gestation stalls to confine sows. A company spokeswoman said Burger King buys "tens of millions of pounds of pork" every year.

It...