Kidney stones in cats and dogs


Supplied by the veterinary team at Animal Anti-Cruelty League Epping, Cape Town

Is your dog or cat suddenly urinating in strange places (like on your bed or the couch) or inside the house when it’s never done so before? Or are they dribbling urine as they walk or lie down? Perhaps there’s blood in their urine or they look like they’re straining or struggling to pee. Overall, they might seem weak, depressed, not want to eat, or even vomit and show clear signs of pain. Your pet could have urinary stones.

Treating stones early is crucial; the longer you leave them, they worse they get, causing pain, illness and possibly even death. Understanding what they are and how they form will help you treat them and keep your pet healthy for many years to come.

About urinary stones

Urolithiasis (bladder stones) refers to the condition of having urinary calculi or uroliths (stones) located anywhere in the urinary tract. They can be present in either the kidney, ureter, bladder or urethra. They can be very hard, can form in anything from a few weeks to several months, and there could be one big stone or many smaller ones. They can be smooth, rough or jagged, and range in colour from white or yellow to a brownish white.

They ultimately irritate the lining of the urinary tract, causing changes in the lining, blood in the urine and, most often, pain. 

The stones can block or partially block the flow of urine, making urination extremely painful or impossible. By reducing or blocking (obstructing) urine from leaving the body, a perfect breeding ground for bacteria is created and the animal can develop infections. 

If obstruction occurs, the bladder cannot be emptied fully; if the obstruction is complete, the dog will be unable to urinate at all. If the obstruction is not relieved, the bladder may rupture. A complete obstruction is potentially life-threatening and requires immediate emergency treatment.

What causes urinary stones?

These stones form due to high concentrations of crystals in the urinary tract and their composition can be affected by diet, urine volume, frequency of urination and genetics.

The most common urinary stones in dogs and cats are composed of the mineral struvite. In almost all dogs, struvite stones form as a consequence of a urinary tract infection (UTI). These stones form slowly and often owners are unaware of any abnormality until the dog’s ability to urinate becomes affected. Other stones can be formed of calcium oxalate, calcium phosphate, uric acid, and other compounds.

Microscopic crystals precipitate out of the urine and, over time, stick together, forming bigger grains, which can then grow into stones – similar to packing little bits of snow together to form a snowball.  

The less diluted the urine is, the higher the concentration of crystals and the greater the likelihood of stone formation. This is why dehydration and/or water high in mineral concentrations can also play a role in stone development in animals prone to them.

Why some animals develop stones

Female patients are at a higher risk for developing bladder infections, thus these stones most commonly form in older, small breed female dogs.

Genetics may also play a role. Certain dog breeds are more prone to them, including Dalmatians, Yorkshire Terriers, Bulldogs, Miniature Schnauzers and Cocker Spaniels, among others. Persian cats are more prone to developing calcium oxalate stones while Siamese may be more prone to struvite stones. Male cats in general are more likely to develop blockages caused by stones. Smaller pets such as chinchillas, hamsters and guinea pigs can also develop stones, usually due to incorrect diet.

Diet is also implicated, as is water intake. Animals that have been deprived of water for some time such as neglected, tethered dogs or long-time strays may also be more prone.

Treatment

Once your pet has urinary stones, they won’t “just go away” on their own, no matter how much water or special food you give them – it’s up to you to help them and then ensure they’re prevented in future. There are three primary treatment options for struvite bladder stones:

1) Feeding a special diet to dissolve the stone(s): The use of therapeutic diets to dissolve struvite bladder stones is often recommended in cases where the risk of a urinary tract obstruction is relatively low.

2) Non-surgical removal: If the bladder stones are very small it may be possible to pass a special catheter into the bladder and then flush the stones out.

3) Surgical removal: Surgery is indicated in animals that have a large number of stones in their bladder if there’s an increased risk that the patient will develop an obstruction in the urinary tract, or should the client wish to have the problem resolved as quickly as possible.

Animals that have had struvite bladder stones will often be fed a therapeutic diet for life. Certain diets can aid in the prevention of stone formation based on the type of stone your pet had. Careful routine monitoring of the urine to detect any signs of bacterial infection is also recommended. It’s also important to ensure that your pet has access to fresh, clean water at all times.

Always seek veterinary advice if there’s any uncertainty, and if you suspect a urinary blockage or infection, see your vet immediately.