Calcium oxalate urinary stones are common in dogs and cats. These irregularly shaped, rounded stones show up well on x-rays due to their calcium content. Although they are more common in miniature schnauzers, bichon frise, shih tzu, Lhasa apso, miniature poodles and Yorkshire terriers, I have also seen them in many other breeds and mixes over my career. In my experience, calcium oxalate stones are more common in males than females. Their owners report a change in their pet’s habits, excessive licking of the penis, straining to urinate and sometimes passing blood.
The cause of calcium oxalate stones is poorly understood. It is thought to be caused by a number of things that cause an acidic urine pH (pH < 6.2), as well as, an increase in the concentration of calcium and oxalate in the urine. Here is a list of some potential causes:
– defective nephrocalcin, a substance in urine that prevents calcium oxalate stone formation.
– excess amounts of calcium, protein, vitamin D and/or sodium in the diet.
– chronic treatment with furosemide
– treatment with high doses of steroids
– certain cancers including lymphoma and those of the anal glands leading to high blood levels of calcium
– metabolic acidosis which means the pH of the blood falls below its normal level.
Unfortunately, there are no dissolution diets for calcium oxalate stones. The stones must be removed via surgery, lithotripsy or urohydropulsion. Once the stones are gone, the goal is to have the dog produce a lot of alkaline urine to keep the stones from reforming. This is achieved by feeding a low protein diet such as Hill’s UD, Hill’s WD or Royal Canin SO. Be very careful using UD or SO in dogs prone to pancreatitis as the fat content may be too high. WD has lower fat but may require additional medication to keep the pH alkaline. I also have the owners add water to the dog’s food to promote frequent urination. I recommend checking urine samples frequently to make sure the chosen diet is working properly.
-Shell, Linda, Urolithiasis, Calcium Oxalate. Canine Associate, VIN, 3/31/2009.
-University of Minnesota, Urolith Center. Canine Calcium Oxalate Uroliths, http://www.cvm.umn.edu/depts/minnesotaurolithcenter/prod/groups/cvm/@pub/@cvm/@urolith/documents/asset/cvm_asset_107726.pdf