Bald Bum! Please help.

Hi.

Can anyone suggest a reason why my Goldline has a bald bum?

She is in a run with 3 other hens and 4 10-week-old chicks.  She is the only one with a bald bum - on close inspection it doesn't look as if the feathers have been plucked as many of the feather follicles are still there.  The patch runs from under her tail, past her bottom, down to her underside.  The area looks quite sore.

In regards to 'pecking order' she is at least second, if not top hen so I don't think it's the others pecking her.

As far as I'm aware she roosts in the hen house rather than sleeping in one of the nest boxes (she's certainly roosting when I close the hen house up for the night).

She seems to be eating well, she's bright and alert, and one of the more friendly and inquisitive of my birds. 

I feel really guilty that I hadn't noticed this until today, so not sure how long this problem has been building.

I have scrubbed the hen house out today with Poultry Shield and sprinkled it with Diatom. 

I haven't used any louse or mite powder directly on her yet, as I wasn't sure if this might be very uncomfortable/painful if this is more of a skin complaint.

Can anyone please help??

Thanks

hi
i,ve got one with a bald bum it's been that way since i got it. I have not seen it been pecked. I tried eveything from foul smelling spray that turned it's white featrhers brown to gentin violet but nothing seems to work. I just gave up it's a great layer and seems very happy. It's bum is quite red but i think thats just it's natural colour.
cheers

Hi. One of my girls has a bolt botty.
When i got my girls they was all bold but Beryl is the only one who hasn't got her french knickers yet 
Her botty is pink but sometimes turns red then pink again like a cemeleon
She is top of the pecking order,eats the most and very active .....and always talking lol 

All in all she is very healthy and active but just has no feathers on her botty