The effect of urine acidification on calcium oxalate relative supersaturation in cats

There is an apparent reciprocal relationship between magnesium ammonium phosphate (MAP, struvite) and calcium oxalate (CaOx) urolithiasis incidence rate in cats. The number of struvite uroliths submitted for analysis over the past 35 years has been decreasing, with an increase in CaOx urolith submissions. Commercial diets aimed to dissolve struvite uroliths are typically acidified, and it has been suggested that dietary acidification increases urinary calcium excretion and the risk of CaOx crystallization. The objective of this study was to assess the effect of urine acidification on the relative supersaturation (RSS) of CaOx in cats, as a representation of crystallization risk. Four diets were extruded to contain identical nutrient contents, but with gradual acidification (0, 0.6, 1.3 and 1.9% sodium bisulphate substituted sodium chloride in diets A, B, C and D respectively). Thirteen adult cats were fed each diet sequentially for a minimum of 10 days. Average urine pH was 6.4, 6.2, 6.0 and 5.9 on diets A, B, C and D respectively (p < 0.0001). Struvite RSS decreased on diets inducing more acidic urine pH (p < 0.0001). Urinary calcium excretion and concentration increased with diets inducing lower urine pH (p < 0.0001), but oxalate excretion and concentration decreased (p < 0.001). CaOx RSS was not different between diets (p = 0.63). These results suggest that a lower diet base excess and resulting urine pH to support struvite dissolution do not increase the risk for CaOx crystallization in the range of urine pH representative of most commercial feline diets. Long-term studies are needed to confirm this.

Nutritional Management of Urolithiasis

Dietary management of urolithiasis in dogs and cats is designed to dissolve calculi when possible and/or reduce the risk of recurrence. The diet must reduce urine relative supersaturation for the particular salt in order to prevent crystallization. To decrease urinary concentrations of crystal precursors, increasing water intake is essential regardless of the stone type. Altering the amounts of dietary precursors of the stone and controlling urine pH is mostly effective for struvite, urate, xanthine, and cystine, but still subject to controversy for calcium oxalate. The investigation of underlying metabolic disorders and close monitoring of animals at risk is recommended.

Pathology and Epidemiology of Oxalate Nephrosis in Cheetahs

To investigate cases of acute oxalate nephrosis without evidence of ethylene glycol exposure, archived data and tissues from cheetahs ( Acinonyx jubatus) from North America ( n = 297), southern Africa ( n = 257), and France ( n = 40) were evaluated. Renal and gastrointestinal tract lesions were characterized in a subset of animals with ( n = 100) and without ( n = 165) oxalate crystals at death. Crystals were confirmed as calcium oxalate by Raman spectroscopy in 45 of 47 cheetahs tested. Crystals were present in cheetahs from 3.7 months to 15.9 years old. Cheetahs younger than 1.5 years were less likely to have oxalates than older cheetahs ( P = .034), but young cheetahs with oxalates had more oxalate crystals than older cheetahs ( P < .001). Cheetahs with oxalate crystals were more likely to have renal amyloidosis, interstitial nephritis, or colitis and less likely to have glomerular loop thickening or gastritis than those without oxalates. Crystal number was positively associated with renal tubular necrosis ( P ≤ .001), regeneration ( P = .015), and casts ( P ≤ .001) but inversely associated with glomerulosclerosis, renal amyloidosis, and interstitial nephritis. Crystal number was unrelated to the presence or absence of colitis and was lower in southern African than American and European animals ( P = .01). This study found no evidence that coexisting chronic renal disease (amyloidosis, interstitial nephritis, or glomerulosclerosis), veno-occlusive disease, gastritis, or enterocolitis contributed significantly to oxalate nephrosis. Oxalate-related renal disease should be considered as a potential cause of acute renal failure, especially in young captive cheetahs. The role of location, diet, stress, and genetic predisposition in the pathogenesis of oxalate nephrosis in cheetahs warrants further study.

An imaging investigation of in situ uroliths in hospitalized cats in New Zealand and in the United States

The submission rates of feline uroliths to laboratories and the composition of uroliths have been reported in studies. The prevalence of uroliths reported on imaging findings has not been published. The objective of this retrospective study was to use imaging data to investigate the anatomical location and the prevalence of macroscopic in situ uroliths in cats. Radiographs, sonograms and imaging reports from two cohorts of cats (from New Zealand (n = 497) and the United States (n = 693)) from 2004‐2013 were reviewed for the presence of in situ uroliths. Uroliths were categorized by their location in the lower or upper urinary tract. Radiographic studies were performed on 43% (212/497) of the cats from New Zealand and 50% (349/693) of the cats from the USA. Sonographic studies were performed on 57% (285/497) of the cats from New Zealand and 50% (344/693) of the cats from the USA. The total prevalence of uroliths was 3% in the New Zealand cohort and 13% in the USA cohort. Lower tract urolith prevalence in the New Zealand cohort was 2.4% (5/212) in cats ≤ 6y and 1.1% (3/285) in cats >6y. Upper tract urolith prevalence in the New Zealand cohort was 0.5% (1/212) in cats ≤ 6y and 1.8% (5/285) in cats >6y. Lower tract urolith prevalence in the United States cohort was 6.0% (11/183) in cats ≤ 6y and 2.9% (15/510) in cats >6y. Upper tract urolith prevalence in the United States cohort was 2.7% (5/183) in cats ≤ 6y and 10.2% (52/510) in cats >6y. The prevalence of uroliths in the upper tract or lower tract was low in the New Zealand cohort compared to that of cats in the USA cohort, irrespective of age category. Geographical location may be important when evaluating risk factors for feline urolithiasis.