Answer: Dry cat foods are usually well accepted by cats, content adequate amounts is essential nutrients, give ‘exercise’ to the teeth thereby reducing the deposition of tartar and are convenient to feed in that they can be left down all day for ad lib feeding.
However, the feeding of dry cat foods has been associated with the formation of plugs of crystalline material in the urinary tract. Plugs of this paste block the urethra of male cats as it goes through the pains. This condition is known as the feline urological syndrome; FUS for short. An effected male licks his pains and strains to pass urine. In the early stage he may pass a little, stained with blood, but when obstruction is complete no urine is pass and the cat shows signs of worsening renal failure, including depression, loss of appetite and vomiting.
In fairness it must be said that other cause of FUS have been suspected, the major one being viral infection and it seems probable that both diet and infection are important in producing it. Castration early in life was suspected, but is now known not to be cause.
There seem to be two main ways in which dry cat foods can assist the development of FUS. One is by causing a reduction in the cat’s water intake. The natural prey of cats contain about 70% of water the same as most canned foods whereas dry foods contain only 8 to 10% water. Careful measurements have shown that, even when ample fresh drinking water is available, the total amount of water is taken in by cats food is much less then that taken by cats fed canned food. With less water is being taken in, the urine becomes more concentrated, and this favors the precipitation of salt in the urine to from the crystalline plug.
Secondly, some dry cat foods used to contain a high level of magnesium salts. Eventually these salts appeared in the urine and contributed to the formation of the crystals, which are composed are magnesium ammonium phosphate. Fallowing an appreciation of the problems, the magnesium content of these foods has been reduced. However, high magnesium levels are naturally present in certain foods, notably fish and beef. The level of in these foodstuffs can be three times those in fish roes, eggs, tripe and conned cats foods.
Cats that have suffered from FUS in the past are the best not fed on a dry cat food, but on a canned product, or food boiled at home, with some additional water mashed into it. If dry food is fed is should be thoroughly soaked in water, milk or gravy to from a sloppy porridge before being presented to the cat. Extra salt should be added to all food given to these animals to stimulate the drinking of more water. Many manufactures now routinely add more salt to their dry diets (up to 3 ½%) to increase water consumption. Clean water should be available at all times. In some case your vet will provide tablet for the cat to take to make its urine more acid, which helps prevent these crystals forming.
Regular exercise with plenty of opportunities to urinate also helps to reduce the chance of FUS recurring. Regular urination avoids large volumes of urine remaining in the bladder for long periods during which the salts are able to precipitate out. Obese, lethargic and elderly cats are less likely then other to exercise and urinate frequently, and it is recommended that these animals should also not be fed regularly on dry foods.
