The Ultimate Guide to Kidney Stones in Dogs by Type (Struvite & Calcium Oxalate)

KidneyDiseasesMeongsiljang Veterinary Advisory Board

Kidney stones in dogs are classified into struvite and calcium oxalate types based on their composition, and the causes, treatments, and dietary management strategies differ significantly between the two. Identifying the specific type of stone is the essential first step in treatment.

What Are Kidney Stones in Dogs? Know the Types First

A veterinarian examining a puppy's kidneys.

Kidney stones in dogs are a urinary tract condition where minerals clump together inside the kidneys, forming hard, stone-like masses. The most critical step is to first identify the specific composition of the stones. Struvite and calcium oxalate stones differ completely in their causes and treatment approaches. Attempting to manage the condition without knowing the stone composition can actually worsen the situation, so analyzing the stone’s makeup is the essential starting point for effective treatment.

Causes of Struvite Stones

Struvite stones form when magnesium, ammonium, and phosphate combine. In dogs, they are most often caused by a urinary tract bacterial infection. Certain bacteria break down urea, making the urine alkaline, which allows crystals to clump together quickly. These stones are more common in female dogs and often begin as an ascending infection that travels from the bladder up to the kidneys.

Causes of Calcium Oxalate Stones

Calcium oxalate stones form when the concentrations of calcium and oxalate in the urine become elevated. They are not related to infection but rather result from a combination of metabolic, genetic, and dietary factors. These stones tend to form in acidic urine and are most commonly seen in middle-aged and older male small-breed dogs. Particular attention should be paid to breeds with a known genetic predisposition, such as Miniature Schnauzers, Yorkshire Terriers, Lhasa Apsos, Shih Tzus, and Bichon Frises.

An elderly small-breed dog sitting next to its water bowl

Struvite vs. Calcium Oxalate: A Quick Comparison

Item	Struvite	Calcium Oxalate
Main Cause	Urinary tract bacterial infection	Metabolic, genetic, and dietary factors
Predisposed Sex	More common in females	More common in males
Urine pH	Alkaline	Acidic
Dietary Dissolution	Possible	Not possible
Recurrence Rate	Low (when infection is controlled)	High (frequent recurrence)
Predisposed Breeds	Miniature Poodle, Cocker Spaniel	Miniature Schnauzer, Yorkshire Terrier

Based on veterinary textbooks (Clinical Medicine of the Dog and Cat, 4th ed., etc.)

Checklist of Main Symptoms of Kidney Stones in Dogs

Kidney stones can progress silently before suddenly worsening. If you notice any of the following signs, please have your pet examined at a veterinary clinic.

Hematuria: Blood in the urine, or urine appearing pink or brown.

Abnormal Posturing During Urination: Frequently sitting down and standing up, or only passing small amounts of urine.

Flank Pain: Avoiding touch or curling up when the lower back or abdomen is touched.

Decreased Appetite: Eating less than usual and showing lethargy.

Vomiting: Sudden vomiting can occur if a stone blocks the ureter.

Emergency Signs Requiring Immediate Veterinary Care

If you notice these symptoms, there is a high likelihood that a stone is obstructing the ureter. This can lead to acute kidney failure, so emergency veterinary care is needed within 24 hours. - Inability to urinate for more than 12 hours - Repeated vomiting and severe lethargy - Severe pain when the abdomen is touched, causing the pet to cry out - Pale gums or a drop in body temperature

Diagnostic Methods for Kidney Stones

The presence, location, and size of stones are confirmed through imaging tests such as abdominal X-rays and ultrasounds. Because the radiopacity of stones varies depending on their composition, stones with low radiopacity may be missed on X-rays alone. Therefore, ultrasound is often more useful for diagnosis than X-ray. While clinical information such as age, breed, sex, and stone shape can help predict composition to some extent, size and shape alone are not sufficient to definitively identify the type. The exact composition can only be confirmed by sending the removed stone for quantitative stone analysis. Urinalysis is used to check pH, crystal type, and the presence of infection, and a plan to prevent recurrence can be established once the stone composition is confirmed.

A puppy undergoing an ultrasound examination at the animal hospital.

Treatment Methods by Type

Kidney stones (nephroliths) are often monitored without immediate removal if they are asymptomatic, but surgical intervention is usually required if a stone obstructs the ureter. Struvite stones can sometimes be dissolved medically using antibiotics to eliminate the causative bacteria along with a prescription stone-dissolving diet. In contrast, calcium oxalate stones cannot be dissolved through diet and require physical removal via surgery or endoscopy. Extracorporeal shock wave lithotripsy (ESWL) may serve as an alternative to surgery, but it is not yet widely available in veterinary practice. The treatment approach depends on the stone’s location and size, as well as the dog’s overall condition, and immediate surgical intervention is necessary in emergency cases where a stone blocks the ureter.

Home Care and Recurrence Prevention Tips

To prevent recurrence after treatment, consistent care is essential.

Adequate hydration: Increase daily urine output to reduce the time crystals have to clump together.

Prescription diet maintenance: Use food formulated to regulate pH and minerals according to the specific type of stone.

Regular urinalysis: Check for pH levels, crystals, and infections every 3 to 6 months.

Weight management: Maintain an ideal body weight and balanced diet to support overall urinary tract health.

Mix in wet food: Dogs eating only dry kibble may not get enough moisture.

Breed-Specific Precautions

Miniature Schnauzers, Yorkshire Terriers, Bichon Frises, Lhasa Apsos, and Shih Tzus have a genetic predisposition to calcium oxalate stones. For these breeds, we recommend annual routine urinalysis starting in middle age (5–7 years). Dalmatians are more prone to uric acid stones and require specific management, while Miniature Poodles and Cocker Spaniels have a relatively higher incidence of struvite stones. Understanding your dog’s breed-specific risks can help with early detection.

Reviewed by a veterinarian

Dr. Tony — Punnawat Phongkittirak

Veterinarian

A veterinarian who majored in veterinary medicine at Khon Kaen University, Thailand, and completed the IVSA program at North Carolina State University in the United States. Drawing on clinical experience at animal hospitals, he works in the pet healthcare field and is dedicated to building a digital care environment that connects pet parents with veterinarians.

Frequently Asked Questions

What is the recurrence rate of kidney stones in dogs?

Calcium oxalate stones tend to recur frequently even after treatment. Struvite stones, on the other hand, have a relatively low recurrence rate as long as reinfection is prevented. Regardless of the stone type, regular check-ups are essential.

Is it really necessary to analyze the type of stone?

Yes, it is absolutely essential. Struvite stones can be dissolved through diet, but calcium oxalate stones cannot. If the stone composition is unknown, feeding the wrong prescription diet could actually cause the stones to grow larger.

Is there a good way to drink water to help prevent stones?

Mixing wet food into their diet or using an automatic water dispenser to keep water flowing can increase intake. Adding a small amount of bone broth or low-sodium meat broth to their water can also be helpful.

Can small stones be passed naturally?

Small stones may pass on their own, but if they block the ureter, they can quickly cause kidney damage. Don’t try to diagnose this yourself—always consult your veterinarian after imaging tests.

Do I need to give my pet this prescription medication for life?

Calcium oxalate stones require lifelong management with a prescription diet, while struvite stones can be transitioned back to a regular diet once they have completely dissolved. However, ongoing monitoring of urine pH is still necessary.

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References

[1] Ettinger SJ, Feldman EC, Cote E. Textbook of Veterinary Internal Medicine, 8th Edition. Chapter on Urolithiasis

[2] Nelson RW, Couto CG. Small Animal Internal Medicine, 6th Edition. Urinary System chapter

[3] Bartges JW, Polzin DJ. Nephrology and Urology of Small Animals, 2011