Some young male cats suffer from a syndrome in which their bladder and urethra become chronically inflamed (irritated). Cats with mild cases suffer pain and discomfort, and may urinate with increased frequency. They also may urinate outside the litter box. Cats with severe cases may develop a life-threatening condition in which they are completely unable to urinate.
This syndrome, known as FUS or FLUTD, is hereditary in nature. In other words, it is caused by an irregularity in some cats’ body chemistry. It is not caused by diet. However, feeding a high quality diet helps to prevent the syndrome in cats who are predisposed to it.
In my practice, cats fed Science Diet and cats fed Purina both have low rates of FUS, so if your cat prefers Purina it probably won’t be a problem. However, cats who are predisposed to FUS can develop troubles no matter what they’re fed. If you’re worried, you can ask your vet to run tests on your cat’s urine to determine if he is predisposed to the problem.