Featherless butts is often a sign of bullying. It is not normal for chickens to have featherless butts, it is actually a cause for concern. The only times it is normal is when they’re moulting, but even then they’re losing a lot of feathers and it doesn’t look that red and inflamed. Your chickens having feathers on they’re butts is a sign that they’re healthy.
Have had several red naked butts here over the years.
Never really found a cause or sure.
The redness came and went on some, eventually it resolved after a molt.
Never really seemed to bother the birds.
The redness on the rear end is due to urates in feces scalding the skin which causes feather loss, redness, swelling and irritation. Put Nu-Stock on it and it will heal the area and prevent any picking.