Bladder stones: How & Why Do They Form?

Jack Russell Terrier urinatingKidney stones are uncommon in dogs, whereas bladder stones (urinary caliculi, or uroliths) are quite common. There is not just one type of bladder stone. The most common type are struvites which usually form when there are certain bacterial types of infections in the urinary tract. The next most common bladder stones are calcium oxalate stones. Other types are urate (uric acid) stones, cystine stones and silica stones.

The reason for the formation of each type of stone is different. Once a dog has developed stones, without preventative measures there is a significant risk that they will get the same type of stones again.

Once the presence of bladder stones have been diagnosed they should be treated. Stones in the bladder can be very irritating to the lining of the bladder and stones will continue to grow. Stones can block the urinary tract, and if the tract is not unblocked, the kidneys will shut down and a dog will die.

  • Prevention of recurrence of stones
  • How do bladder stones form?

    All types of stones are formed when minerals in the urine start to precipitate out. The minerals can either precipitate onto bacterial matter if there is a bladder infection (see Urinary Tract Infections: Bladder (Cystitis) & Urethral Infections) or form crystals which can then grow larger.

    Why do bladder stones form?

    • Bacterial infection of bladder
    • Urine pH – whether it is acid or alkali
    • High concentration of one or more minerals in urine
    • Genetics

    Bacterial infection of bladder

    Bacterial infections of the bladder can promote conditions that cause a type of stone called a struvite to form. Bacterial debris can provide a surface on which minerals in the urine can precipitate on and start the growth of a stone.

    Some bacteria can also change the pH of urine making it more alkaline. A number of bacteria have an enzyme called urease. In urine, the component that has the highest concentration is urea (after water). Urease hydrolyzes urea to ammonia, and a proportion of the ammonia becomes ammonium ions. This increases the pH of urine making it more alkaline. Bacteria that are common in bladder infection that have urease include Staphlococci and Proteus.

    Urine pH – whether it is acid or alkali

    When the pH of urine increases, becoming more alkaline, this promotes the formation of struvites.

    Decreasing the pH of urine, making it more acid, favors the formation of calcium oxalate, uric acid stones and cystine stones.

    High concentration of one or more minerals in urine

    The concentration of minerals in the urine can be affected by a number of things including;

    • How much a dog drinks; not drinking enough will lead to concentrated urine and high levels of minerals
    • Levels of minerals and protein in food
    • Individual metabolism and/or genetics of a dog


    Some dogs are predisposed to form stones. Some breeds, and even some lines within breeds have an increased risk of developing certain types of stones. The susceptible breeds are listed below for the individual types of stones.

    Breeds susceptible to struvites include Labrador Retrievers, Dachshunds, Bichon Frises, Yorkshire Terriers, Shih Tzus and Miniature Schnauzers. Some lines of Cocker Spaniels have a metabolic predisposition to formation of struvites.

    Breeds susceptible to calcium oxalate stones include Lhasa Apsos, Minature Poodles, Bichon Frises, Yorkshire Terriers, Shih Tzus and Miniature Schnauzers.

    Breeds susceptible to urate (uric acid) stones include Dalmations and English Bulldogs, plus any dog with a congenital portosystemic vascular shunt (born with abnormal blood vessels that move blood away from the liver).

    Breeds susceptible to cystine stones include Newfoundlands of both sexes, and mainly males in the following breeds; Chihuahuas, Dachshunds, Basset Hounds, Irish Terriers, Yorkshire Terriers and English Bulldogs.

    Breeds susceptible to silica stones are German Shepherds and possibly Labrador Retrievers, Golden Retrievers and Miniature Schnauzers.


    Next Page – Bladder Stones: Types & Diagnosis

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