They can, it depends if you want them to or not. Some who feed organically do not like soybean in their birds diet so may feed soy free organic feed. Soybean that is GMO has been suspected of being responsible for food allergies and there are those that feel there are better proteins for their hens than soy. Soy has been linked to allergies in humans and dogs as well. Some dog foods are now no corn, wheat, or soy as believed to be common dog allergens. Soybean is often in chicken feed even organic feed unless you choose not to. It is estimated that approximately 80% of soybean market is GMO and nonGMO may be better but some just do not take a chance and will remove soy from the diet. There are organic feeds that offer no corn or soy but of course more expensive. Scratch and Peck is one. Corn is suspected to be more of a filler by some and there are better proteins out there for feed. It depends on what you believe
or subscribe to.