The cat was re-evaluated five weeks after initiation of therapy. During the three-week interval between evaluations, the cat
remained asymptomatic. Its micturition pattern was normal. Evaluation of a urine sample collected by cystocentesis revealed
no abnormalities (SG=1.049, pH=6.0). Uroliths were not detected by survey radiography (Figure 4, ). At that time, no evidence
of hematuria, inflammation or crystalluria was detected by urinalysis; the urine pH was 6.0. After the insurance month of
dietary management, therapy with Prescription Diet s/d was discontinued.
Figure 4: Survey lateral abdominal radiograph of the cat described in Figure 1 obtained five weeks after initiation of management
with a struvitolytic diet. There are no radiodense uroliths.
Prevention of recurrence
Although there have been no reports of controlled studies designed to evaluate the frequency of recurrence of struvite uroliths,
the general consensus of opinion based on clinical experience is that recurrence is a common but unpredictable event. Therefore,
the owners were advised of the availability of diets designed to minimize several risk factors associated with formation of
Table 2. Mineral composition of 8,711 feline uroliths and 524 urethral plugs submitted to the Minnesota Urolith Center during
In our clinical experience, diets formulated to reduce urinary concentration of magnesium and to acidify urine to a pH of
approximately 6.0 to 6.3 are effective in minimizing recurrence of naturally occurring sterile struvite urocystoliths in male
and female cats. No attempt was made to determine whether acidification and/or low magnesium diets were the major factors(s)
responsible for beneficial results. Therefore, we recommended that the cat be fed a high-moisture (canned) struvite prevention
diet. We emphasized to the owner that reduction of some risk factors for formation of struvite crystals, including promoting
formation of less alkaline or more acidic urine, is one of several risk factors for calcium oxalate urolithiasis. Therefore,
we recommended periodic re-evaluation of the patient. In the event that significant calcium oxalate crystalluria developed,
appropriate adjustments in dietary management would be necessary.
Epidemiological data from the Minnesota Urolith Center revealed a dramatic increase in the occurrence of feline calcium oxalate
uroliths associated with a decline in struvite uroliths for more than a decade. But during the past two years, the trend has
been a decline in the number of calcium oxalate uroliths associated with an increase in the number of struvite uroliths. We
hypothesize that dietary factors are influencing these changes.
Dr. Osborne a diplomate of the American College of Veterinary Internal Medicine, is professor of medicine in the Department
of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota.
Dr. Lulich, a diplomate of the American College of Veterinary Medicine, is a professor in the Department of Small Animal Clinical
Sciences, College of Veterinary Medicine, University of Minnesota.