Red Diaper Rash like found on my chickens bottoms.

[Arrowheadfarm]

Half of my 10 chickens have a strange diaper like rash on their bottoms. At first, I was thinking this was just a result of molting over winter...but half of my hens never regained feathers on their bottoms and have this horrible rash. When I touch their bottoms, the area seems hot. Has anyone ever encountered anything like this? Please share your suggestions for dealing with a bad rash on a chickens bottom. The rash area is about the size of softball. Hens are about 16 months old.

 

[Firefighter Chick]

do they have diarrhea? have you checked for external parasites?

 

[mamabigbird]

I noticed one of my hens had a rather red looking bottom around the vent.
They are in mid-molt right now but after a close look discovered that they had lice nits attached to the base of their feathers.
I'm treating them with poultry dust.
The other thought is, do they free range? Could they have dust bathed in some stinging nettle or other noxious weeds?

 

[Arrowheadfarm]

A few do have loose stools...but not sure if they are the same birds with the rash. What is diarrhea a sign of? How do you treat it if it continues?