Influence of a Low Carbohydrate, Dry Formulated Diet on Urinary Saturation for Calcium Oxalate and Struvite in Healthy Adult Female Cats
Urolithiasis is common in cats and calcium oxalate is the second most common mineral occurring in uroliths. Obesity is associated with increased risk for feline calcium oxalate urolith formation, and is often managed by feeding a low carbohydrate diet. In some human beings, consumption of a low carbohydrate diet is associated with increased calcium oxalate urolith formation. We hypothesized that feeding a commercially available low carbohydrate diet to healthy adult female cats will increase urinary excretion of calcium and oxalate, decrease urinary excretion of magnesium and citrate, induce aciduria, and increase urinary saturation for calcium oxalate when compared with a commercially available adult maintenance diet.
Six healthy, spayed female cats, aged 4-7 years, and weighing 3.5-6.5 kg, were evaluated. Cats were randomly assigned to be fed a commercially available maintenance diet (Purine ONE adult chicken and rice dry formulation, Nestle Purina) or a low carbohydrate diet (CNM DM dry formulation, Nestle Purina) in a cross-over design. Diets were fed for approximately 6 weeks at which time 24-hour urine samples were collected using a modified litter box. Twenty-four hour urine samples were mixed, the volume recorded, and pH, sodium, potassium, chloride, calcium, magnesium, phosphorous, citrate, oxalate, and ammonia concentrations were determined. Molar concentrations of these analytes were entered into a computer program (EQUIL 89d, University of Florida) for determination of relative supersaturation for calcium oxalate monohydrate and dihydrate, and struvite. Data were analyzed using 1-tailed, paired t-tests; p < 0.05 was significant.
Body weight did not change between diet periods. Consumption of the low carbohydrate diet was associated with significantly higher urine pH (6.96 ± 0.26 vs 6.11 ± 0.15), ammonia excretion (0.50 ± 0.22 vs 0.11 ± 0.08 mM/kg/24hr), citrate excretion (0.036 ± 0.032 vs 0.021 ± 0.016 mM/kg/24hr), and sodium excretion (3.72 ± 1.56 vs 1.85 ± 0.67 mEq/kg/24hr), and significantly lower magnesium excretion (0.33 ± 0.15 vs 0.98 ± 0.68 mg/kg/24hr) and urinary relative supersaturation for calcium oxalate dihydrate (0.52 ± 0.29 vs 0.99 ± 0.49) when compared with the adult maintenance diet. No significant difference was found for urinary volume, urinary excretion of calcium, chloride, creatinine, oxalate, phosphorous, or potassium, or urinary relative supersaturation for calcium oxalate monohydrate or struvite.
Consumption of a low carbohydrate diet by healthy adult female cats did not increase risk for formation of calcium oxalate or struvite urolith formation, and was associated with lowering risk for calcium oxalate dihydrate formation.