I also meant to add in my prev post above that with advances in bunny health and nutrition and with most bunnies living indoors,
rabbits are living a much longer life span than previously..... Specialists are now saying we can expect a well-cared for rabbit, getting proper vet care and diet and living indoors to live a average life of 7-11 years. It's possible that sludge and bladder problems were not seen in bunnies who never got that old and/or that live outside.