"The term FUS (Feline Urological Syndrome or FLUTD...Feline Lower Urinary Tract Disease) is a broad expression that covers cystitis or bladder infections in the female and cystitis and urinary blockage in the male. The most common feature of FUS is the presence of struvite crystals, which consist of magnesium-ammonium-phosphate. Bacteria are often present...the result and not the cause of FUS.
The ash content, and especially the magnesium content, of cat food was formerly thought to be significant in the production of struvite crystals, but recent experiments where excess magnesium was added to the food showed that this did not increase the incidence of FUS. FUS occurs almost exclusively in cats fed a diet, either partially or completely, of dry food. As many of you know, cystitis can be very annoying with the cats constantly trying to pass a few drops of urine, wherever they happen to be. However, urinary blockages can be fatal in males as the toxic wastes build up in the blood due to backpressure from the bladder into the kidneys, which can no longer filter out urine."

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