Urinary stone disease (urolithiasis) is a common clinical problem in dogs. The disease presents itself in two forms: cystic (bladder) calculi and urethral calculi. Cystic stones are found mainly in females and appear when urinary tract bacterial infection within the bladder causes a shift in the urine pH, which in turn causes the crystals to form. The two most common types of crystals generated are struvite and calcium oxalate crystals. Breeds susceptible to bladder infections that can prompt the formation of small stones are boxers, poodles, dalmatians, dachshunds, German shepherd dogs, pugs, and Irish and cairn terriers.
Urinary stones form when microscopic crystals precipitate in the urinary system. Struvite or magnesium ammonium phosphate uroliths are the most common uroliths in dogs. They also may contain a small amount of calcium phosphate or calcium carbonate. Staphylococcus and Proteus are commonly associated organisms. Urethral stones occur in male dogs and are seldom caused by infections; rather a metabolic disease is responsible for crystal formation. Struvite uroliths may occur in all breeds; however, those commonly affected include female miniature schnauzers, miniature poodles, bichon frises, and cocker spaniels, shih tzus, Yorkshire terriers, and lhasa apsos. The female schnauzer is an exception, as they develop calcium oxalate uroliths more frequently than struvite uroliths.1
Calcium Oxalate Uroliths
The incidence of calcium oxalate (CaOx) urolithiasis in dogs has increased steadily over the last two decades. Oxalic acid is widely distributed in nature where it commonly occurs as its insoluble mineral salts. Plants produce deposits of calcium oxalate which is the calcium salt of oxalic acid. Calcium oxalate uroliths are thought to be caused by increased concentration of calcium in the urine which, in turn, is caused by increased absorption of calcium from the gut, a kidney defect, or an underlying diseases (for example, primary hyperparathyroidism). Increased dietary intake of oxalate (for example, vegetables high in oxalates, grass, vitamin C) may play a role in the formation of calcium oxalate uroliths. In shih tzu, miniature schnauzer, bichon frise, lhasa apso, and Yorkshire terrier, there is a strong tendency for males to form calcium oxalate stones.1
Other urolith types, including cystine, xanthine, silica, calcium phosphate, sodium pyrophosphate and dried solidified blood calculi (DSBC) are less commonly reported.1
Theories on the cause of the increasing incidence of calcium oxalate over the last couple of decades include increased feeding of acidified commercial diets; changes in dietary content of calcium, magnesium, phosphorus, or oxalate; decreased water consumption; an increase in sedentary lifestyles of many dogs and cats and, in dogs, trends favoring ownership of small breeds that are more prone to calcium oxalate uroliths.1
Recently, it has been hypothesized that enteric colonization of Oxalobacter formigenes, an anaerobic bacteria which exclusively relies on oxalate metabolism for energy, is linked to decreased risk of calcium oxalate urolithiasis or both in humans and laboratory animals and that decreased enteric colonization of the organis is a risk factor for calcium oxalate urolithiasis in dogs.2 Humans can overwhelm the ability of their kidney to excrete the increased dietary load by consuming juices such as kiwi, spinach and beetroot, calcium intake and ingestion of excess of vitamin C.5
Clinical signs are similar to those seen in dogs and cats with other bladder disorders and include increased frequency of urination, painful urination, excessive licking at the genitals, and occasionally blood in the urine. Increased thirst, increased volume of urine, and urinary incontinence are rarely associated with bladder stones and are more typical of kidney disease and diabetes.Radiographs of the entire urinary system are taken to determine if stones are present in the kidneys, ureters (ducts that carry urine from the kidneys to the urinary bladder), bladder (the most common location for urinary stones), and urethra (a tube which connects the urinary bladder to the outside of the body.)
Treatment depends on the size and location within the urinary tract. Stones that become lodged in the urethra require immediate veterinary medical and surgical intervention. Extraction of urethral calculi by transabdominal cystoscopy and urethroscopy and ransvesicular percutaneous cystolithotomy are surgical procedures used to treat urethral obstructions resulting from calculi in dogs 3,4. These are usually small and enter the urethra from the bladder where they form. They progress down the urethra until they reach a location where the narrow diameter will not permit further passage. A male dog whose urinary tract is completely plugged by one or more stones requires immediate emergency care. Catheterization is performed in an attempt to dislodge the stones pushing them back into the bladder and freeing up the flow of urine. Most of the time, these stones must then be removed from the bladder surgically. Smaller struvite stones or crystals can often be effectively managed only with special diets designed to dissolve the stones. While urinary acidifiers can be useful, some doctors discourage their use, as the exact dosage that is safe and effective is often not known. If urinary acidifiers are used for short-term acidification, a natural therapy such as cranberry extract might be preferred to conventional medications (such as methionine).
Other therapies to consider for the pet with bladder stones include Coenzyme Q10, alfalfa (to alkalinize the urine), dandelion leaf, goldenseal, horsetail, marshmellow, plantain, Oregon grape, uva ursi, yarrow and maitake mushrooms. These therapies can be used in conjunction with conventional therapies as needed. The natural treatments are widely used with variable success but have not all been thoroughly investigated and proven at this time. Consult your veterinarian.
Diet for Dogs with Bladder Stones
Dietary therapy is useful for treating and preventing struvite stones in pets. Since the struvite stones form in urine with a high pH (alkaline urine), diets should help to maintain a low pH (acidic urine). Diets with animal-based protein sources are most important in maintaining an acidic pH, while vegetarian or cereal-based diets are more likely to cause and alkaline urine. Homemade diets are preferred for dogs with chronic bladder disorders such as bladder stones. If processed foods must be fed, most holistic veterinarians prefer canned diets, which contain large amounts of water, rather than dry foods.
Important: Before you start to feed your dog or cat a home-prepared diet, it is strongly recommended that you discuss your decision with your veterinarian or a holistic veterinarian. It is essential that you follow any diet's recommendations closely, including all ingredients and supplements. Failure to do so may result in serious health consequences for your pet.
Prevention of Urinary Stones
Because the rate of recurrence is relatively high even after a successful treatment, preventive measures should be taken to help lower the odds, including special diets. To help prevent bladder infections, make sure the dog is given an opportunity to urinate at least every 6 to 8 hours. The longer urine is retained in the bladder, the more likely it is to become alkaline and to develop infection. Provide plenty of clean drinking water to keep the bladder flushed of bacteria and to encourage frequent urination. Cranberry juice (either mixed in with your dog's food or administered to the mouth) stops certain bacteria from adhering to the bladder wall; ascorbic acid is also helpful for acidifying urine, as well as building up the immune system.
- Canine and feline urolithiasis: Examination of over 50 000 urolith submissions to the Canadian Veterinary Urolith Centre from 1998 to 2008
- Gnanandarajah JS, Abrahante JE, Lulich JP, Murtaugh MP. Presence of Oxalobacter formigenes in the intestinal tract is associated with the absence of calcium oxalate urolith formation in dogs.
- Libermann SV, Doran IC, Bille CR, Bomassi EG, Rattez EP. Extraction of urethral calculi by transabdominal cystoscopy and urethroscopy in nine dogs.
- Runge JJ, Berent AC, Mayhew PD, Weisse C. Transvesicular percutaneous cystolithotomy for the retrieval of cystic and urethral calculi in dogs and cats: 27 cases (2006-2008).
- Primary and secondary hyperoxaluria: Understanding the enigma