Urinary Crystals in Cats: Welfare and Dietary Management
Types of Feline Urinary Crystals
The two most important types of urinary crystals in cats are struvite (magnesium ammonium phosphate) and calcium oxalate. Struvite is most common in cats with urinary tract infections (bacteria producing urease which increases urine pH, promoting struvite formation) or cats fed high-magnesium, high-phosphorus diets. Calcium oxalate is more common in older neutered male cats and is associated with hypercalcaemia. Urate, xanthine, and other crystal types are less common.
Welfare Impact of Urolithiasis
Urinary stones (uroliths) cause welfare impact proportional to their size, number, and location. Small crystals in the urine may cause irritation and cystitis signs. Bladder stones (cystolithiasis) cause haematuria, dysuria, and predispose to urethral obstruction. Urethral obstruction (most common in male cats due to narrower urethra) is a welfare emergency causing acute pain, inability to urinate, and rapidly fatal acute kidney injury if untreated.
Diagnosis and Assessment
Urinalysis (specific gravity, pH, sediment examination for crystals and red/white blood cells) is the primary diagnostic tool. Bladder stones are demonstrated by ultrasound or radiography. Stone type cannot always be determined by radiographic appearance; urinalysis, dietary history, and breed provide clues. Definitive diagnosis requires laboratory analysis of retrieved stones (quantitative analysis).
Struvite Management
Struvite stones in cats secondary to UTI can often be dissolved by treating the infection (which removes the urease-producing bacteria, allowing urine pH to normalise) and feeding a dissolution diet. Prescription struvite dissolution diets (Hill's s/d, Royal Canin Dissolution) modify urinary pH and mineral concentrations to dissolve existing stones within 4-8 weeks. Prevention involves treating underlying UTI, maintaining appropriate urine pH through diet, and ensuring adequate water intake.
Calcium Oxalate Prevention
Calcium oxalate stones cannot be dissolved medically and require surgical or minimally invasive removal (voiding urohydropropulsion or cystoscopy for small stones; cystotomy for larger stones). Prevention involves: wet diet feeding to increase water intake and dilute urine; avoiding excess calcium and oxalate supplementation; dietary phosphorus restriction (reduces calcium excretion); and treatment of underlying hypercalcaemia. Regular urinalysis monitoring identifies recurrence early.