Bladder stones (uroliths) are formed when minerals clump together in the urine. The action is like that of rock candy: Once a small area gets started, the clumping continues and the stones become larger and larger.

There are almost a dozen different kinds of stones, and each has a unique cause and thus a different prevention. Some stones have a genetic basis (cystine and uric acid stones); some may be diet-based (calcium oxalate): and others are started by chronic bladder infections (struvite stones). Preventive measures cannot be started until stone content is identified.

All stones passed or removed surgically must be sent for analysis. There are stone analysis labs at the veterinary schools at the University of California at Davis and the University of Minnesota at Minneapolis/St. Paul.

Although stones sometimes can be dissolved with diet (often requiring many months), most large stones are removed surgically. This minimizes damage to the interior of the bladder, shortens treatment time, allows for the proper analysis of the stone and often is cheaper in the long run.

Once the type of stone is identified, potential preventive measures can be pursued. The most common type of bladder stone (more than 60 percent) in dogs is called struvite (a combination of magnesium, ammonium and phosphate). This stone is usually created as a result of chronic cystitis (bladder infections), tends to form in alkaline urine and is worsened by excess protein. Once struvite stones are removed, aggressive treatment helps prevent recurrence. Feeding a low-protein diet that creates an acidic urine is also important.

Many of the rarer stone types must be treated with specific drugs. Some types of stones simply cannot be prevented.

The therapy diets create a urinary tract environment in which stone recurrence is less likely. For example, Hill's Prescription Diets S/D and C/D are low in magnesium (the main mineral that forms the stones), increase the dog's water consumption (which dilutes the minerals and encourages frequent voiding), provide adequate but not excessive amounts of protein and create an acidic urine. These diets may help prevent recurrence in dogs with struvite stones. On the other hand, dogs with urate or silica stones can be fed Hill's Prescription Diet U/D to keep the urine alkaline.

If the dog will not tolerate the diet or the owner cannot afford it, alternatives can be tried. Meat-based diets tend to produce acidic urine, while diets with a vegetable protein source create an alkaline urine. Dogs with alkaline-based stones may be switched to a meat-based diet with lower protein, while dogs with acidic-based stones need a diet or medication that will alkalize their urine.

Author(s): Wilcox, Bonnie, D.V.M.
Publication: Dog Fancy
Issue Date: April 1994