URINARY STONES IN DOGS AND CATS: Two Very Different Outcomes




Both dogs and cats can develop urinary stones, but they often have very different results. They can be dramatically large, like the orange-sized stone in the image above or be the size of a grain of sand and deadly. The difference, of course, is the width of the urethra.


Until the stones cause a blockage or irritation, and the pet develops UTI symptoms, the pet parent often has no idea that there is a problem. X-rays or ultrasounds are often required to diagnose the problem. Whereas dogs can have kidney stones, cats tend to have stones (known as calculi or uroliths) in the bladder or the tube leading to the bladder or the one leading to the outside world.


Unlike the dog, cats can develop small crystals in the urinary tract not associated with a UTI. These calculi are made when naturally occurring minerals in the urinary tract system, clump to form these crystals. Females are more able to pass the crystals, however, males can (and often do) experience blockage of the ureter. When this occurs, it is an emergency and if left untreated, the cat can die within 24-48 hours. It is important to note that both male dogs and cats are susceptible to urinary blockage. There is no treating this issue at home or “waiting it out”. The pet must be sedated, and a catheter inserted to remove the blockage and allow for normal urine flow.


Feline bladder stone

What we know about calculi, is how they develop, but not necessarily why. Certain internal environmental conditions must be present including a prolonged high concentration of the calculi-forming materials and increased time of the presence of crystals within the urinary tract. That's why it's important for your pet to drink adequately and be allowed to urinate on a regular basis. Expecting your pet to hold urine for extended hours is not healthy.


For the most common stones, improper pH of the urine can encourage stone development. Urinary tract infections, diet, and genetics may also play a part. The environment of the urinary tract in cats and dogs needs to have a pH of approximately 6.2- 6.5. Cats tend to have a more acidic pH. (The lower the pH, the more acidic while the higher the pH, the more alkaline). Ranges too acidic (below 6.0) or alkaline (over 7.0) should be further investigated.


Uroliths or stones fall into three categories. Knowing which stone is more prevalent is essential to knowing how to treat and feed the patient to avoid problems in the future.


The most common stones or crystals are:

  • struvite - high in magnesium in urine that is too alkaline

  • oxalate - too much oxalate or too little liquid can form stones

  • urate - generally caused by a genetic abnormality that causes a defect in the metabolism of uric acid.



Struvite crystals are the most common in both species. The best prevention for a cat is a diet low in magnesium and ash, and for dogs, preventing urinary tract infections.


Signs of Urinary Tract Stones:

  • Straining to urinate

  • Frequent attempts to urinate with little production

  • Trying to urinate in inappropriate places (in the house or outside the litterbox.

  • Vocalization or other signs of distress

  • Blood in the urine

  • Behavioral changes (ex. hiding)


Female dogs with bladder stones can often go undiagnosed because of the smooth edges of the stones. It's when the stone impedes urine flow that symptoms, we are most likely to recognize, develop. One the other hand, crystals/stones the size of a grain of sand can block the urine flow and create an acute medical emergency. Without medical intervention, that cat can die within 24-48 hours.


Male cats who are repeatedly blocked may need to have a perineal urethrostomy.

A PU surgery removes the narrowest part of the urethra, the tube that transports urine from the bladder to the penis. A new opening is created so that urine no longer flows through the penis. He will, essentially, urinate like a female cat.


Both cat and dog patients that have a history of stones are most often put on special prescription diets that are lower in protein to produce less ammonia. Examples are Hills Prescription C/D or Royal Canin S/O. This is the standard treatment for dogs and cats who have suffered from a history of bladder stones. Lower urinary phosphate and magnesium are also goals of prescription diets. which can help prevent certain stones. As long as they remain on this food, the likelihood of developing further problems is drastically reduced.


While prescription diets can be expensive, repeated surgeries and treatment of bladder stones are even more expensive. Care Credit ®, the health credit card that I highly recommend, will cover prescription diets, allowing you to pay for the food over time.


When the cost of prescription diets is absolutely impossible, over the counter foods such as Purina One Urinary Tract Formula, can help lower the ph and magnesium in the urinary tract environment.

It may be possible to use certain urine acidifiers such as potassium citrate, cranberry, or Vitamin C to help maintain a healthy urinary environment. In pets with a history of crystals or stones, never add acidifiers without consulting with your veterinarian.


Other than feeding foods to help prevent stones/crystals, there is no home treatment proven to dissolve stones already created. This is a situation that requires the professional expertise of a veterinarian.

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