Oh interesting, I have a gut feeling that indoor buns with no outdoor access may get a higher % :?
I think part of this is that if a rabbit is indoors you notice things quicker, and intervene where as an outdoor bun may have a bit of gas that passes without the owner noticing, also I think there are often lots of man made fibres buns can chew indoors which can cause problems, and I would think if a bun has access to grass a lot they would have a better digestive system..
I am not saying outdoors buns are healthier, it is swings and roundabouts I think?
All mine are indoors, Gus and Sweetpea have had stasis but nothing too serious