red rump

I have a 7-8 year old red sex link battery hen named dodo. She has had no vent feathers for about six months where she originally did. Now she has stopped laying, she has bad diarrhea, she is not eating and drinking, she is lethargic, her rump is soft, red and dry. If someone could please help...

I have three hens. One is a RIR named brownie, one is I think a white rock named snowball. Then there is my little ex-battery hen named dodo. She is about 7-8 years old. She has a clipped beak but she still eats and drinks normal. Over the last couple of months I have noticed she has feather...