Sorry, I don't have photos. When I saw it, the skin was very noticably red, not just around the vent but her whole backside, and her butt feathers looked like dreadlocks. So I immediately set out fresh water w/ more acv than usual and gave them yogurt. The next day the dreadlocks were about half gone and she was pink, not red but not regular skin either. This morning the butts are all clean. Poops on the board look normal, no puddling or excessive wetness on the pdz. There is also no unusual odor. (pdz keeps my coop smelling fairly fresh and I would notice an unusual smell)
All 4 of my hens tend to have poop remains on the butt feathers at times. I have, in the past, checked for vent gleet, mice, lice and found nothing. The skin then was not pink, just normal looking. It's like the feather shaft and skin is clean but there's something white (urates?) on the very outside tip of the feathers, maybe 4-5 spots, and then it's gone when next I look for it. Someone had said the poop is not clearing the feathers on it's way out.
So, I reassessed my treats, feed, etc and it improved until this episode. When they get melon I can tell more loose poops on the board, so I dole it out in smaller measure and even then it's not often. There are only 2 of us at home and not many leftovers, occasionally some fish or vegetables, but they mainly get layer feed (when it's gone they'll all get flockraiser until the new chicks change to layer).
They are not overweight, are alert and active. The only thing about miss dreadlock is that she will head up to bed fairly early, like 6 pm. She's always done this. When I go out to button up the babies in their tractor she'll come flying out hoping for treats and then stay out until the others go in. That doesn't strike me as odd, since Rosie waits until the ador door beeps before heading that way--she'd stay out all night if it didn't beep.
I'm also dealing with scaly leg mite, dipping their legs every morning, but I don't think that would make a difference. The dreadlocks are not greasy like her belly feathers.