My chicken has a lump or tumor on her chest--what should I do?
You are probably seeing your chicken's crop. A chicken's crop is a part of her digestive system, and is located on her front, usually on her right-ish breast. It will be smaller in the morning before she has eaten, and larger after she is full. It holds food before it goes to the proventriculum, and before entering the gizzard to be ground up with the grit she eats. Chickens need grit because they don't have teeth, although chick starter is finely milled enough so that a chicken does not need to grind it up further with grit. Chickens will need grit once they begin eating treats and food other than chick starter. If your chickens free range, they will probably pick up grit, gravel or small stones on their own, but we usually provide extra just in case.
If the lump doesn't change in size or is hard all the time (don't press too much, because you can force the food back up into your chicken's mouth and cause her to aspirate her food--very dangerous!), your chicken might have an impacted crop, and you will need to get her to a vet. An impacted crop can happen if she doesn't get enough gravel to digest her food, or if you feed her long strands of grass or hay thatare too fibrous for her system to handle. Grass is a nice treat when chickens eat it on their own, but keep in mind that a browsing chicken will eat only small pieces, not long strands that can get wound up into a ball in her crop! If that happens, other food won't pass, and she will need veterinary attention, or she could starve.