The relative frequency of struvite and calcium oxalate uroliths in cats has markedly changed over the last 15 years. In the 1970’s and 1980’s, struvite urolithiasis predominated, but in the 1990’s, calcium oxalate superceded struvite as the most common urolith type. At the University of Minnesota, the frequency of feline uroliths composed of calcium oxalate rose from 2% in 1984, 5.6% in 1989, 27% in 1993, 37% in 1995, 46% in 1998 to 48% in 1999, and a similar trend is apparent at the stone laboratory at University of California, Davis. This change in urolith composition at least partially reflects dietary modification, such as urinary acidification, of proprietary cat food to reduce the prevalence of struvite urolithiasis. The pathogenesis of feline calcium oxalate urolithiasis is poorly understood. A proportion of cats have associated hypercalcemia, but most cats with calcium oxalate uroliths are normocalcemic. Calcium oxalate uroliths tend to develop in middle-to-older age cats of typical weight. There is no gender predilection. Factors associated with an increased risk of calcium oxalate urolithiasis include feeding urine-acidifying diet, feeding a single brand of cat food, maintaining cats in an indoor only environment and being of the Persian breed.
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