For the Nutritional Management of Cats with Struvite Related Feline Lower Urinary Tract Disease (FLUTD). FLUTD is a condition often associated with the formation of crystals in the urinary tract that can cause numerous painful symptoms for your cat. The two most common types of crystals that form in the cat's urinary tract: struvite and oxalate. Prescription Diet c/d Feline cat food is formulated to provide nutritional management of cats with struvite-related FLUTD. Prescription Diet c/d contains reduced building blocks of struvite and produces an acid urine pH, lowering the chance that struvite crystals will form. The nutritional formulation of Prescription Diet c/d may also be useful for pets with a variety of conditions.