Juno's kits have yet to have a poopy butt with the reduced pellets and handfuls of grass (fescue and timothy).
I had a horse with chronic diarrhea that the vet said to get on grass as much as possible and believe it or not, the fresh grass tightened her right up.
I'm still having trouble getting my bunnies to eat hay, but I have reduced their feed which is good. Wilburs bum still gets poopy, but it seems to be better.