Kidney stones in dogs form when minerals in urine become too concentrated and crystallize into solid masses. The two most common types, struvite and calcium oxalate, account for roughly 85% of all canine urinary stones, and each has a distinct set of causes. Understanding which type your dog is prone to matters because the triggers, treatment, and prevention strategies are different for each one.
The Main Types of Kidney Stones
Struvite stones, made of magnesium, ammonium, and phosphate, are the most common type in dogs, making up about 50% of all canine urinary stones. Calcium oxalate stones are the second most common at roughly 35 to 50% of cases (the proportion has been rising over the past two decades). Less common types include urate, cystine, and silica stones, each with its own specific cause.
The type of stone determines everything about how it’s managed. Struvite stones can often be dissolved with dietary changes, while calcium oxalate stones cannot and typically need to be physically removed. That distinction starts with what caused the stone in the first place.
Struvite Stones and Urinary Infections
In dogs, struvite stones are almost always linked to urinary tract infections. Certain bacteria produce an enzyme called urease, which breaks down urea in the urine and releases ammonia. This makes the urine more alkaline, and struvite crystals thrive in alkaline urine. The combination of high ammonia, elevated pH, and the magnesium and phosphate already present in urine creates the perfect conditions for these stones to form and grow.
Because the infection drives the stone, treating the infection is a core part of resolving the problem. Dogs with recurring UTIs are at ongoing risk. Female dogs get struvite stones more often than males, largely because they’re more prone to urinary tract infections.
Calcium Oxalate Stones and Metabolism
Calcium oxalate stones form through a different mechanism. Rather than infection, these stones are driven by the body excreting too much calcium into the urine, a condition called hypercalciuria. This can happen in three ways: the gut absorbs too much calcium from food, the kidneys fail to reabsorb calcium properly, or calcium is pulled from bone into the bloodstream.
Research on breeds prone to these stones (Miniature Schnauzers, Bichon Frises, and Shih Tzus) found that affected dogs have higher-than-normal blood calcium levels compared to stone-free dogs of the same breed, age, and sex. Interestingly, the evidence points to intestinal hyperabsorption of calcium as the most likely culprit in these breeds, rather than calcium leaking from bone. These dogs’ bodies simply pull too much calcium from their diet, and the excess ends up in the urine where it binds with oxalate and crystallizes.
Acidic urine also promotes calcium oxalate formation. Some commercial diets formulated to prevent struvite stones include acidifiers like ammonium chloride, which can inadvertently increase urinary calcium excretion and raise the risk of calcium oxalate stones. This is one reason a stone’s composition needs to be identified before changing your dog’s diet.
Breed and Genetic Risk Factors
Genetics play a significant role in stone formation. Dalmatians and English Bulldogs carry a genetic defect in how they process purines, a compound found in many proteins. This defect leads to excessive uric acid in the urine and makes them prone to urate stones specifically. The amount of purine in their diet directly influences how severe the problem becomes.
Miniature Schnauzers, Bichon Frises, and Shih Tzus are genetically predisposed to idiopathic hypercalciuria, putting them at elevated risk for calcium oxalate stones. Small breeds in general tend to develop calcium oxalate stones more frequently, while larger breeds and those with recurrent infections are more likely to form struvite stones. If your dog belongs to one of these breeds, routine monitoring with imaging every three to six months can catch stones before they cause problems.
How Diet Contributes to Stone Formation
Diet doesn’t usually cause kidney stones on its own, but it can tip the balance in a dog that’s already predisposed. Several dietary factors matter depending on the stone type.
For struvite stones, high-protein diets increase the amount of ammonium and phosphate in urine, both building blocks of struvite crystals. Diets designed to prevent struvite are low in protein, but that creates a catch: low-protein diets make urine more alkaline, which is exactly the environment struvite crystals prefer. To counteract this, preventive diets include acidifying ingredients like the amino acid methionine.
For calcium oxalate stones, the dietary picture is more nuanced. Reducing calcium intake too aggressively can backfire. Calcium in the gut actually binds to oxalate and prevents it from being absorbed into the body. Cut calcium too low, and more oxalate enters the bloodstream, reaches the kidneys, and ends up in the urine. High-oxalate treats like certain vegetables and fruits also contribute. Much of the oxalate in a dog’s body comes not from food directly but from the body’s own processing of other nutrients, which limits how much dietary changes alone can accomplish.
Water intake is one of the most straightforward dietary factors. Concentrated urine is the common denominator across all stone types. When dogs don’t drink enough, urine becomes supersaturated with minerals, giving crystals the opportunity to form. Increasing water consumption dilutes those minerals and is a first-line prevention strategy regardless of stone type.
Urine pH and Its Role
The acidity or alkalinity of your dog’s urine has a direct influence on which stones can form. Struvite crystals form readily in alkaline urine (higher pH), which is why UTIs that raise urine pH are so strongly linked to struvite stones. Calcium oxalate, cystine, and urate stones, by contrast, are more likely to develop in acidic urine.
For dogs prone to calcium oxalate, cystine, or urate stones, the goal is to keep urine pH neutral to slightly alkaline. If fasting urine pH drops below 6.5, veterinarians may recommend alkalinizing supplements like potassium citrate to bring it up. For struvite-prone dogs, the opposite applies: mildly acidic urine helps prevent crystal formation. This is why knowing the specific stone type is essential before making any dietary or supplement changes.
Signs That a Dog Has Kidney Stones
Many dogs with kidney stones show no symptoms at all. Stones are frequently discovered incidentally when a vet takes an X-ray or performs an ultrasound for an unrelated issue. When symptoms do appear, they can include blood in the urine, recurrent urinary tract infections, abdominal pain (your dog may tense their belly, hold an unusual posture, or move less than usual), vomiting, lethargy, and poor appetite.
Dogs can pass a kidney stone the way a person does, with the stone moving from the kidney into the ureter toward the bladder. In people, this is notoriously painful. Dogs tend to be stoic, making it harder to recognize when they’re in distress. A stone lodged in the ureter is a serious concern because it can obstruct urine flow and cause pressure damage to the kidney.
How Kidney Stones Are Treated
Treatment depends entirely on the stone type, size, and location. Struvite stones can often be dissolved without surgery through a combination of antibiotics (to clear the underlying infection) and a therapeutic diet that reduces the mineral precursors and acidifies the urine. Progress is typically monitored with imaging after about four weeks of treatment.
Calcium oxalate stones cannot be dissolved medically and need physical removal. Traditional surgery through the abdomen remains an option, but minimally invasive techniques have expanded significantly. Laser lithotripsy, which breaks stones into fragments using a laser delivered through a scope, is one approach. For smaller stones in the bladder or urethra, the scope can be passed through the urethra directly. For larger or more numerous stones, or in very small dogs (under about 5 kg), a percutaneous approach through a small incision in the abdomen may be used instead.
For urate stones in breeds like Dalmatians, management combines dietary purine restriction with medication to reduce uric acid production. Periodic imaging helps catch new stones while they’re still small enough to flush out without surgery.