Vetsupply: Hill\'s Prescription Diet c/d Urinary Stress Chicken Cat food pouches is specially made to address the complex condition of FLUTD (Feline Lower Urinary Tract Disease) in cats. The two most common types of crystals that form in the urinary tract of cats are struvite and calcium phosphate. Struvite crystals and stones usually develop from a combination of urine saturated in magnesium, ammonium and phosphorus and alkaline urine pH