I've been known to throw a bit of anything vaguely appropriate into piles of composting manure: charred pieces of wood, bits of mineral block, bones. The basic idea being, given enough time the bacteria and fungus will break it down and make it available for use by some future plant.
I also create more compost than I use as soil. Consequently, I have time to let those solid pieces sit and break down. If I start a new pile it is with the knowledge that I may never see the bottom of it again. It is a good problem to have.
Every spring I send about four to eight feed sacks worth of aged compost home with my Mom for Mother's Day. With the early spring, I sent it home with her this past weekend. This year I was a little surprised by what I found.
Is it goat, sheep or deer? Odds are sheep, though thinking about the age of this particular pile of rabbit manure, it could have been any of them.
I put a shovel of dirt back on top of it. Young rabbits will be in the cage above it and adding strata of excrement to the topsoil soon enough. Maybe it'll surprise me again in another few years or maybe it will have returned to dust before shovel goes that deep again?