Kidney stones are rare in dogs. Bladder stones are
common. Stones that form in the bladder may pass into the urethra. All dogs can
develop bladder stones. Breeds with an increased incidence include the
Miniature Schnauzer, Dalmatian, Shih Tzu, Dachshund, and Bulldog.
Bladder and urethral stones may be large or small, single or multiple, and
may pass spontaneously or obstruct the lower urinary
tract. Stones in the bladder eventually cause painful urination and blood
in the urine.
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Most bladder stones are struvites (that is, they’re composed of magnesium
ammonium phosphate). They form in an alkaline urine and are usually preceded by
infection. The bacteria and urinary sediment form a nidus around which the
ammonium phosphate is deposited.
Uric acid stones form in an acid urine, and are frequently associated with
inherited alterations in urate metabolism. Dalmatians and Bulldogs are
Other stones are calcium oxalate and cystine
stones. Cystine crystals have been found in Newfoundlands and many other
breeds. There is a genetic test offered by VetGen, OptiGen, and PennGen to
detect carriers and affected dogs with this problem. Silica stones are rare;
they occur most often in male German Shepherd Dogs. These stones are not
usually associated with a preexisting bladder infection.
Stones that are large or numerous can sometimes be palpated through the
abdomen. In most cases the diagnosis is made by X-ray. A contrast dye study may
be needed for definitive diagnosis. Stones not visible on an abdominal X-ray
can often be seen by ultrasonography or IVP. A urinalysis is routinely obtained.
Stones that pass spontaneously and those that are removed surgically should
be analyzed, if possible, since the composition of the stone influences the
treatment of any remaining and future stones.
Treatment: Bladder infection, if present, is treated as described for
Cystitis (page 414). In many cases the stones can be dissolved over weeks or
months by feeding the dog a special diet. Struvite stones dissolve in an acid
urine, requiring a diet low in magnesium and protein-accomplished by feeding
Hill’s Prescription Diet s/d, or Royal Canin Urinary SO 13. Uric acid stones
respond to a low-purine diet (Hill’s u/d), along with the drug allopurinol.
Cystine stones also respond to Hill’s u/d, along with drugs that dissolve
cystine. Feeding a vegetarian diet, such as Royal Canin Vegetarian Formula, may
help prevent urate stones. There are no methods currently available for
dissolving calcium oxalate and silica stones. However, diets and supplements
can be used to reduce the risk of recurrence.
Surgical removal is the treatment of choice for urethral stones that cause
obstruction and for bladder stones that fail to respond to a diet change and
medication. Surgery is also indicated when medical treatment is contraindicated
because of congestive heart failure, or when there is a need for
more rapid resolution of symptoms.
The formation of new stones occurs in up to 30 percent of cases. The dog
should be seen and checked at regular intervals. Your veterinarian may
recommend long-term dietary changes and/or the addition of supplements such as
vitamin C, raspberry seed extracts, or cranberry extracts.