Many cats suffer from flutd feline lower urinary tract disease a complex and painful disease of the lower urinary tract frequently associated with the formation of crystals which can lead to bladder stones the two most frequent types of crystal which form in the urinary tract are struvite and calcium phosphate hills prescription diet feline sd cat food helps to reduce both of these types of urinary stones the two most frequent types of crystal which form in the urinary tract are struvit