Hi! I just bought a chick and once I got home I noticed that he/she has a protruding butt as well. So your chick grew up to be fine and normal? No issues? Mine is acting normal. Eats, sleeps, poops okay. I did noticed that the chick would try to get at it's butt. Not sure if it's trying to peck at its own butt or tries to scratch it with it's beak, but it's not able to reach it. So I'm just hoping that he/she makes it.
I am not sure, but I think many of these vent problems can be due to dehydration as in the earlier case of shipping chicks that are a few weeks old. I don't know how chicks can go through the mail at that age and survive. It is hrd enough on day old chicks who can survive 3 days without water, only because they are absorbing their yolk. Feed store chicks are shipped, and shipped chicks need to be given plenty of fluids early on, checked for the pasty putt that can result for up to a week or more, and make sure hat they have a cool spot in a brooder to escape too high temperatures. I would give a little molasses as a laxative, dip it's beak into water every hour a few times to get it to drink, and put a little oil around the vent.