There are three main types of stones in the urinary tract that affect dogs, and while no breed is off the hook, some are more commonly affected:
Struvite stones, composed largely of magnesium, ammonium,
Susceptible breeds: miniature schnauzer, bichon frise, miniature
poodle, cocker spaniel.
Calcium oxalate stones, composed of — you guessed it — calcium
Susceptible breeds: bichon frise, miniature schnauzer, Lhasa Apso, Yorkshire terrier, shih tzu.
Urate stones, made of urates, which are types of salts.
Susceptible breeds: Dalmatian, English bulldog. (The reason Dalmatians are more commonly afflicted than other breeds is that they have a genetic defect that affects the metabolism of protein. A side effect of that defect is the development of urate stones.)
Interestingly, both urate stones and struvite stones can potentially be slowly dissolved with a therapeutic diet rather than removed surgically — but not if they are lodged in the urethra, making it impossible to urinate. In cases in which urination has virtually stopped, there’s no time to lose. The stone has to be removed right away via surgery.