Bladder stones in dogs form when dissolved minerals in urine crystallize and clump together into solid masses. The specific cause depends on the type of stone, but the most common triggers are urinary tract infections, concentrated urine, dietary imbalances, and genetic predispositions. Understanding which type your dog has (or is prone to) matters because prevention and treatment differ significantly for each one.
Struvite Stones: Infection Is the Main Driver
Struvite is the most common type of bladder stone in dogs, and in most cases, a urinary tract infection is directly responsible. Certain bacteria, particularly Staphylococcus and Proteus species, produce an enzyme called urease that breaks down urea in urine. This chemical reaction raises the urine’s pH, making it more alkaline, and releases ammonium ions. Both changes create the perfect environment for magnesium, ammonium, and phosphate to crystallize into struvite stones.
The infection doesn’t just set the stage for stone formation. It actively sustains it. As long as the bacteria keep producing urease, the urine stays alkaline and minerals keep precipitating out. This is why treating struvite stones almost always means treating the underlying infection at the same time. In some cases, struvite stones form without any infection at all, though this is less common. These “sterile” struvite stones can develop when a dog’s kidneys handle acid and minerals abnormally.
Calcium Oxalate Stones: Metabolism and Diet
Calcium oxalate stones are the second most common type and behave very differently from struvite. They tend to form in acidic urine rather than alkaline urine, and infection usually plays no role. Instead, the causes are metabolic. Dogs that excrete too much calcium in their urine, or that produce an abnormal version of a protein called nephrocalcin (which normally prevents crystal formation), are at higher risk.
Certain hormonal conditions also raise the odds. Dogs with Cushing’s disease (overactive adrenal glands) or elevated blood calcium levels are predisposed to calcium oxalate stones. Diet plays a significant role too. Risk factors include excessive calcium supplementation, excessive calcium restriction (which paradoxically increases oxalate absorption from the gut), high-protein diets, high sodium intake, low potassium, low phosphorus, and diets with too little moisture. Dogs fed exclusively dry kibble may face higher risk simply because they take in less water overall.
Unlike struvite stones, calcium oxalate stones cannot be dissolved with diet changes or medication once they’ve formed. They have to be physically removed.
Urate and Cystine Stones: Genetics at Work
Some stone types are driven almost entirely by genetics. Urate stones form when a dog can’t properly break down purines, which are compounds found in DNA and concentrated in organ meats. Dalmatians are the classic example because of a breed-wide genetic mutation that affects how their liver and kidneys process uric acid, but the same mutation has been identified in Bulldogs, Black Russian Terriers, and other breeds. Dogs with liver shunts (abnormal blood vessels that bypass the liver) also develop urate stones because the liver can’t do its job of converting uric acid into a more soluble compound.
Cystine stones result from a different inherited defect where the kidneys fail to reabsorb the amino acid cystine from urine. When cystine accumulates, it crystallizes. This condition has been documented across many breeds, with Newfoundlands, English Bulldogs, and Dachshunds among the more commonly affected.
How Concentrated Urine Accelerates Stone Growth
Regardless of the stone type, concentrated urine is a universal risk factor. When a dog doesn’t drink enough water, or loses excessive fluid through panting or exercise, the minerals in urine become more tightly packed. Think of it like dissolving sugar in water: a small glass can only hold so much before crystals start forming at the bottom. The veterinary target for dogs prone to stones is a urine specific gravity below 1.020, meaning the urine is relatively dilute. Keeping urine dilute means minerals are less likely to reach the concentration needed to crystallize.
This is one of the simplest factors you can actually influence. Feeding wet food instead of dry kibble, adding water to meals, and encouraging frequent drinking all help keep urine dilute. Frequent bathroom breaks matter too, because urine sitting in the bladder for long stretches gives crystals more time to form and grow.
Signs Your Dog May Have Bladder Stones
The two hallmark signs are blood in the urine and straining to urinate. Blood appears because the stones physically rub against the bladder wall, irritating and damaging the tissue. Straining happens because inflammation and swelling narrow the urethra, and muscle spasms make it harder for urine to pass. Your dog may squat or lift a leg repeatedly, producing only small amounts of urine each time, or seem uncomfortable during urination.
Some dogs show subtler signs: urinating more frequently, having accidents indoors, or licking their genital area excessively. Small stones can sometimes pass on their own, but larger ones can partially or fully block the urethra. A complete blockage is an emergency. If your dog is straining to urinate and producing nothing, or only tiny squirts, that’s a sign the flow is obstructed.
How Bladder Stones Are Found
Most bladder stones show up on a standard X-ray because they’re dense enough to block the X-ray beam. Calcium oxalate and struvite stones are reliably visible this way. Urate and cystine stones, however, are less dense and can be difficult to spot on plain X-rays, especially when they’re small. When stones are suspected but not visible, vets may use ultrasound, contrast-enhanced X-rays (where dye is injected into the bladder to outline the stones), or CT scans.
Identifying the stone type is critical because it determines the entire treatment approach. The only way to confirm the mineral composition is to analyze a stone after it’s been removed or passed. Urine pH, crystal type in a urinalysis, breed, and imaging appearance can offer strong clues, but lab analysis of the actual stone is the gold standard. The Minnesota Urolith Center, one of the leading stone analysis labs, maintains specific treatment protocols for over a dozen different stone compositions in dogs alone.
Diet and Prevention by Stone Type
Prevention strategies are tailored to whichever stone type your dog forms, and getting it wrong can actually make things worse. A diet designed to prevent struvite (which lowers urine pH) could promote calcium oxalate formation, and vice versa.
For struvite-prone dogs, the goals are keeping urine pH between 6.0 and 6.5, maintaining dilute urine, and preventing or promptly treating urinary tract infections. Therapeutic diets designed for struvite can actually dissolve existing stones over several weeks, which makes surgery avoidable in many cases.
For calcium oxalate, prevention focuses on avoiding excessive calcium, sodium, and protein in the diet while ensuring adequate potassium and moisture. Since these stones can’t be dissolved, the emphasis is entirely on preventing new ones from forming after removal. Urate-prone dogs benefit from low-purine diets that limit organ meats and certain proteins. Cystine-prone dogs need diets that reduce cystine excretion and keep urine alkaline enough to prevent crystallization.
Across all stone types, water intake is the single most controllable factor. Wet food, water added to kibble, and access to fresh water throughout the day form the foundation of any prevention plan. If your vet has identified your dog’s stone type, ask specifically about urine pH and concentration targets so you can monitor whether the dietary strategy is working.