RIR has bare red back half

[AuntChickie]

1yr old RIR has no feathers on back half? Tail and wings are fine. *No roosters* Started 5 months ago. Thought it was moulting but hasn’t improved. Not worse either. Other 3 hens are fine. Housing/nest box is loft with pine shavings. Haven’t noticed pecking from other hens. Affected hen eats-drinks-lays... does not seem bothered by affliction?

 

[rebrascora]

The feather damage on the top of her back looks like it might be rooster damage (do you have a rooster?) but that swollen abdomen is another matter altogether and I'm afraid to say it is most likely terminal. Swelling in that location is usually Salpingitis which is an infection in the oviduct where it becomes impacted with a mixture of egg and cheesy pus often referred to as "lash egg". It builds up into a huge mass, sometimes the size of a grapefruit with more eggs backed up behind it, that the chicken has no means of passing and eventually the mass grows so big it presses on the lower intestines and prevents the bird eliminating waste and they die from toxic poisoning or heart failure.
If you hundreds of dollars to spare and can find a good vet, they may be able to surgically remove the oviduct (sometimes called a hysterectomy) and it's infected contents and give the chicken antibiotics and a hormonal implant to prevent further ovulation but the implants need to be replaced every 3-6 months at a cost of $120+ a shot. The risks from the initial surgery are very high so I would not recommend going that route unless you are financially very well off.... even then, I'm not sure it is fair to put the hen through it.
I know you will not want to hear this, but the kindest thing you can do for her is to end her suffering. Sadly these reproductive ailments are all too common in hens. If you do nothing, she may even rupture. That skin looks like it is pretty much stretched to the limit and the redness might just attract a peck or two from her flock mates which could cause her to just split open.... a pretty horrible death.

 

[AuntChickie]

No roosters. Condition has persisted 5 months with no change. She lays a normal egg every day. No discharge.

 

[rosemarysugar]

Maybe mites or allergy?

 

[AuntChickie]

If mites, I would expect others to have evidence of mites as well? But other hens are fine. What would she be allergic to? Chickweed? Henbit?