Extremely Swollen Underside
Sorry about your chicken. Have you just started noticing the enlarged area recently? Could you post a picture of her vent for us to see what you see? There can be several conditions with swelling below the vent described by many chicken owners in past threads, ranging from a possible hernia, to a teratoma, to possible cancer. Many of these enlarged areas are there for a long time, and the hen seems to get along without a problem. I would like to make sure that she doesn't have a prolapsed vent which is where the insides poke through the vent.