Alright, I have found a solution to poop stains!
Here's what I did.
I took a small container (I cut off the top of a soda can and just used the bottom) and put some dawn BLUE dish soap ( blue might not make a difference, but that's what kept coming up in my research so I decided to stick with that) along with some hydrogen peroxide. I just poured some in, no exact measurments.
Then, I wet kadins legs, and stuck a toothbrush into my mixture. Make sure you use a soft toothbrush so it's not too rough on their skin. I simply brushed in onto the skin and brush pretty good to make it all in the fur. It took a lot of elbow grease.
I let it sit for a few minutes and then washed it off. The results were awesome!!
It obviously still isn't perfect, but I think doing this a few more times would drastically improve his butt appearance
However, hydrogen peroxide can be very drying, so definitely use some kind of moisturizer. Like a good conditioner or rub some coconut oil or vitamin e oil.
However, hopefully kadins health will improve soon, we shuffled horses around and put him with the geriatric Arabs! There's 6 now, and the are all between 23 and 30. They are all grey, and all get pelleted feed instead of hay. Kadin has been having some trouble digesting his food, and they gave him a few weeks after getting his teeth floated to see how he would improve, but unfortunately he hasn't. So, since he can't fully chew his food, his poop has pretty long hay pieces in it, and he basically has some really bad diarrhea.
So, it should stop poopy butt from getting much worse!!