Comparison of the total and individual purine content of commercial maintenance dog foods and therapeutic dog foods that may be prescribed to prevent urate urolithiasis

Urate is the third most common component of canine uroliths. Dogs with a genetic mutation or hepatic dysfunction excrete more urate salts and are predisposed to urate urolith formation. Documentation of total and individual purine content in commercial diets is clinically important because feeding diets containing fewer purines reduces urinary uric acid excretion and urolith formation. Nine purine metabolites were measured using ultra-high performance liquid chromatography and tandem mass spectrometry in samples of 3 batches of 14 dry and 10 canned diets from 3 manufacturers, including low-protein diets, vegetarian diets, diets designed to prevent urate uroliths, and maintenance diets. Concentrations were compared among diet groups using a linear mixed model design. Total concentrations are reported as least squares means and 95% confidence intervals. Total purine content (μmol/Mcal) was lower (P < 0.0001) in prescription (736; 475–1053) than maintenance (2459; 1866–3133) diets, and lower in dry (464; 316–641) than canned (1704; 1327–2127) diets. Among dry prescription diets, vegetarian diets and urate urolith prevention diets contained the least purines, followed by low-protein diets; all contained < 630 μmol/Mcal purines except for one low-protein diet. Hypoxanthine concentrations were proportionately lower in vegetarian diets. Feeding dry vegetarian, urate urolith prevention, and some low-protein prescription diets to dogs should reduce urinary uric acid excretion more than feeding wet equivalents. However, factors that affect urinary urate crystallization, like urine pH and dilution, should also be considered. These findings will facilitate the selection of low-purine diets for individual dogs susceptible to urate urolithiasis.