Tonight when I let my girls out for their arvo free range time in the yard I noticed one was dirty around the bum so I got a tub of warm soapy water to wash her and when I picked her up and had a closer look I realized there was a much worse problem. Her bum hole is fine and she has been pooping but it almost looks like she has been straining to push out an egg and has ripped her bum open somehow? It is quite leathery and around the edge on one side there was a maggot infestation. I cut back the feathers, soaked her in warm salty water then used tweezers to pick out all the maggots. The area was hot and appeared to be full of liquid so I put a pin in and clear fluid started coming out. I made a small incision and we let out about 1 1/2 cups of liquid. I could not find an egg that may have caused the initial obstruction and the fluid was mostly clear except for a small pea sized thing that looked and felt the consistency of a cooked egg yolk. We emptied almost all the fluid out and rewashed her, then used swabs to put hydrogen peroxide on the infected area. We have looked online at a lot of sites about what it could possibly be but have no clear definition on what it could be. She is separate from the other hens in her own small cage with food and water and a warm bed for tonight and we will keep her separated until she is better enough in our eyes to return. I am really just writing, wondering if you anyone has come across anything like this before? She has not been lethargic and as soon as I put food down after draining the sac she began eating. I just want to repeat that the large round mass you see is very leathery and not sensitive to her at all. The fluid has a strong odour but not of infection, it smelt like my chicken coop usually does when it needs a clean out, I suppose urine. We did this ourselves and are looking for the answer online because we cannot afford a vet right now. *Update - She has made it through the night and seems a little lethargic this morning.