Ammonium urate or urate stones in dogs are common in Dalmations and bulldogs. Dalmations lack the enzyme needed to convert uric acid in the urine to allatoin. As a result, their urine contains high concentrations of uric acid leading to formation of uroliths (stones) in the urinary tract. Urate uroliths are also seen in dogs with portosystemic (liver) shunts due to increased levels of ammonium and uric acid. I have also seen urate stones form in dogs with other types of liver disease, especially cirrhosis.
Diagnosing these stones can be challenging, as they do not show up on routine x-rays. I usually recommend an abdominal ultrasound to visualize the urinary system as well as the liver. I also perform blood work, urinalysis and urine culture. Urate stones form in acidic to neutral urine and can on rare occasions be associated with bacterial infections that produce urease. Most of these patients have low levels of albumin and blood urea nitrogen as well as abnormal bile acids when tested.
Treatment will depend on where the stones are located and whether the dog has liver disease. If the stones are stuck in the urethra or ureters, surgery or lithotripsy is required to remove the obstruction as soon as possible. If the stones are in the urinary bladder and the dog does not have a shunt, medical dissolution can be tried. The dog is fed Hill’s UD which is formulated to reduce uric acid production. The dog is also placed on a drug called allopurinol to further reduce uric acid production. In my experience, this treatment protocol works in about 40% of the dogs.
After the stones are gone, the dog is placed on lifelong therapy to prevent recurrence. For dogs without liver problems, I use either Hill’s UD or Royal Canin UC. I check urine frequently for pH and urate crystals. If crystals recur, I add allopurinol back into the dog’s treatment until the crystals are gone. Dogs with liver disease including portosystemic shunts are more challenging. My patients have done the best when their liver disease is treated. I usually use HIll’s LD or Royal Canin Vegetarian Formula combined with lactulose and sam-e. For all dogs with any type of urinary stones, I recommend increasing the dog’s water consumption to produce a more dilute urine which helps prevent stone formation. This can be done in a variety of methods including adding water to the food, giving ice cubes as treats or flavoring the water.
-Grauer, Gregory. Urolithiasis, Clinician’s Brief, NAVC April 2014, 27-29.
-Shell, Linda. Urolithiasis, Ammonium Urate, VIN Canine Associated, 1/12/2009.