Calcium oxalate stone formation and dietary factors | Vets & Clinics

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Calcium oxalate stone formation and dietary factors

Urolithiasis, which is the formation of sediments composed of poorly soluble crystalloids, is a common problem in dogs. The four most common minerals found in dog uroliths are magnesium ammonium phosphate (struvite), calcium oxalate, ammonium urate and cystine.

Veterinary medicine and care

Kidney stones can cause pyelonephritis, urinary obstruction, kidney atrophy, azotaemia and kidney failure.

What is the influence of diet?

The incidence and composition of uroliths is influenced by different factors, such as breed, sex, age, diet, anatomical abnormalities, urinary tract infections, urine pH and drug treatments. The key to the effective treatment and prevention of urolithiasis, which often has a high rate of recurrence, is identifying these risk factors. This has led to the increasing use of dietary treatments to both dissolve and prevent the formation of uroliths, although some minerals are easier to dissolve than others.

Implementing preventive measures is extremely important, as calcium oxalate uroliths do not respond to medical dissolution so mechanical removal becomes necessary.

Diet plays an important role at both an intestinal level and with respect to urine composition. The main risk factor for calcium oxalate urolithiasis is calcium and oxalate urine supersaturation  in the presence of relatively high calciuria. The relationship between intestinal calcium absorption and oxalic acid absorption is clinically significant, as a reduced calcium concentration increases oxalate absorption, which maintains or increases the risk of stone formation.

CANNED WET FOODS

A study in dogs with urinary tract disease associated with calcium oxalate crystals versus healthy dogs, in which both groups were fed a specific diet, concluded that wet food formulas containing large amounts of protein, fat, calcium, phosphorus, magnesium, sodium, potassium, chloride and moisture and low quantities of carbohydrate may reduce the risk of calcium oxalate stone formation in dogs.

Dietary recommendations

The main aim of dietary urolithiasis management is to produce urine with a low calcium oxalate saturation (click here for more information):

  • By increasing water intake and, therefore, urine output to reduce the concentration of crystalloids in the urine.
  • By modifying urine pH to increase the solubility of the crystalloids.
  • By modifying the diet to reduce the number of crystalloids excreted in the urine.
     

Patients should not be given any treats or dietary supplements containing calcium, vitamin D or a lot of vitamin C, as they may favour an increase in calcium and/or oxalate excretion. Foods that prevent the formation of calcium oxalate stones should stimulate water consumption but should not be restricted in protein, calcium or phosphorus.

Dietary treatment will help prevent kidney and urinary damage in dogs affected by calcium oxalate urolithiasis, acting at three levels by promoting macro and micronutrition and delaying disease progression.

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