It’s really difficult, you’ve tried so many things. Arthritic pain prevents him from reaching down to eat his cecotropes, but it’s not really the reason why he always has lots of mushy poop. My Bam has a sensitive tummy and is prone to poopy butt. Some times I have to give him butt baths often, and then there are periods when he doesn’t need butt baths. You could try changing pellets, that’s about the only thing you don’t mention having tried. If you could find a pellet that doesn’t have soy you could try that. In The USA, Sherwood has pellets without soy. In Europe there’s some pellets from JR Farm and Bunny Dream that don’t have soy.

I had a bunny with chronic poppy butt too, and he hated his butt baths. He was my first rabbit and in the beginning, before I knew what was going on with him, he would get so sore from the poopy butt that he would freeze up and twist around in pain when he peed, and even hold his urine to avoid the pain. That resulted in bladder sludge- poor bunny.

Has your bunny been tested for parasites or infection/bacteria in his poop? My rabbit went on metronidazole for an ear infection, and it actually helped with the poopy butt, which made me wonder if there was an underlying infection or parasites from living outdoors. You can bring in their poop for testing, if you haven’t done that already.

Switching pellets is a great idea- they can cause lots of issues. I ended up stopping pellets, and that helped. I would feed unlimited hay, of course, a variety of greens, and make “cookies” from Critical Care and pumpkin, to give in place of pellets. That would be something you might run by your vet though.

I’m sorry you and your rabbit are going through this- I know how difficult and saddening it is to see them uncomfortable, and have to subject them to butt baths, even though we have to. Good for you for rescuing him and giving him so much love- he is a lucky rabbit to have found you!