Sorry if these questions sound silly, but I am new to chickens! I bought 6 chicks of 3 varieties. One little chick is not thriving....she is now about 4 weeks old, but the other chicks are triple her size. Her feathers are also very slow to come in..the other chicks are getting their colors but she is still yellow and downy with the exception of new wing feathers. She eats and drinks, scratches, pushes her way into the food, and does all the things the others do. I've added an antibiotic to their water (about 3 days ago). I separated her and one other chick at night so that she could get extra food, but nothing seems to be working. Today, I put them all in the outside coop for the first time. When I brought them in tonight, I noticed that the right side of her breast was enlarged and very hard near the wing joint. Her mate protects her, but I think the others may be peaking her? An old post on this site mentions it is probably her crop, but I treated it with iodine just in case. Any suggestions? Overall symptoms: Failure to thrive Failure to develop feathers Hard swollen right breast Otherwise she seems healthy, but I still worry about her.