Kirsten - does Luna get Cosequin mixed in her food? It's usually used as a joint supplement to prevent arthritis, but it also strengthens the lining of the bladder and urethra so that germs and crystals don't do as much damage. And it's just a chicken/fish flavored version of something I myself take, glucosamine/ chondroitin, so it's been pretty extensively studied.

Love, Columbine