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“But doc, he was on that diet you prescribed. How did he get stones again?” Does that sound familiar? Like many of you, I have heard this question countless times from owners of dogs and cats prone to stone formation. It’s frustrating for owners who have already put their pet through surgery and think that the prescribed diet will prevent future urolithiasis to discover that those pesky rocks have returned. It is equally frustrating for us to see dogs that have had 3 or more cystotomies for recurrent calcium oxalate stones or to have to manage a male bulldog with a scrotal urethrostomy. This situation highlights the importance of understanding the role of diet in a variety of urolith types, what it can and cannot do, and managing client expectations.
Exploring the role of nutrition
For many years it has been known that diet plays a role in causing—and managing—urolithiasis in people and in small animals. The relationship between urease-positive bacterial urinary tract infections and struvite uroliths in dogs was noted more than 70 years ago.1 In the 1980s, studies by Carl Osborne and his team highlighted the significance for dissolving these uroliths of maintaining urine acidity through dietary modification in addition to antimicrobial treatment.2,3 New discoveries about the role of urine pH and dietary magnesium levels in the risk of feline struvite urolithiasis led to changes in commercial cat food formulations in the 1980s and drastically altered the prevalence of these uroliths. However, after years of decline in cats, a recent study indicated a rise in their prevalence at a major urolith center.4 Although there is a clear role for diet in the dissolution and prevention of struvite urolithiasis in both dogs and cats, prevention of lower urinary tract infection with urease-positive bacteria is also crucial in dogs.
There are several veterinary therapeutic formulations available for the dissolution and prevention of struvite urolithiasis in the dog and cat. Previously, a protein-restricted diet was used for dissolution but not advised as complete maintenance for long-term prevention. In the past 10 to 15 years, the veterinary therapeutic food industry has explored healthier, more balanced diets and their impact on the dissolution of struvite uroliths.5 Several studies, like the one published using BLUE Natural Veterinary Diet W+U, demonstrated dissolution of naturally occurring feline struvite uroliths in less than a month.6 Our study also demonstrated the importance of feeding the diet exclusively to achieve the best results. Dietary management of struvite urolithiasis is extremely successful in cats and dogs if risk factors for UTI are also addressed.
Unfortunately, diet has been shown to be less effective in prevention of calcium oxalate uroliths in dogs and cats. As a greater understanding of struvite urolithiasis reduced its prevalence, the frequency of calcium oxalate grew in both cats and dogs, according to several prominent urolithiasis laboratories. In fact, an unfortunate consequence of the trend toward urinary acidification of cat foods may have led to an increase in calciuresis and risk of nephro- and cystolithiasis.7 The predisposition to calcium oxalate urolithiasis is complex, multifactorial, and incompletely understood. Factors such as male sex, neutering, breed, and obesity have been identified as predisposing to their development. They are frequently recurrent, and management strategies usually revolve around increased water intake, reduction of urinary calcium excretion, an increase of inhibitors, and surveillance with minimally invasive removal of small uroliths.8 Currently, the available diets and research in calcium oxalate prevention focus on reduction of relative supersaturation (RSS) by reduction of calciuresis, oxalate, and other promotors in the urine, increased urinary citrate and volume, and subsequent dilution of lithogenic elements. Two ways to accomplish this may be to add sodium chloride or potassium chloride to the diet.9, 10
A closer look at calcium oxalate uroliths
At this time, there is no commercial diet available that will dissolve calcium oxalate uroliths, and even with the reduction in RSS and induction of isosthenuria, dietary prevention of these uroliths has been disappointing. The majority of dogs, and many cats, who develop calcium oxalate urolithiasis will have a recurrence. Therefore, it is important to educate owners on the role a veterinary therapeutic diet plays in this disease. No calcium oxalate diet has been shown to prevent recurrence, but delayed recurrence is more likely with its use. Surveillance and removal of very small stones using voiding urohydropulsion and other minimally invasive techniques are likely the best approach to avoid surgery.
Urate urolithiasis is most commonly seen in dog breeds with the SLC2A9 transporter mutation or with congenital portosystemic vascular shunts. There is a block to the complete metabolism of dietary purines in the liver and an increase in urinary excretion of uric acid. Historically, dogs were placed on very low protein diets to reduce the purine content; however, there other diets are now available that use egg whites or vegetarian sources of protein to reduce the purine content while maintaining an adequate protein level.11
Cats can also develop urate uroliths secondary to liver dysfunction, but more commonly they are idiopathic, with no identified genetic or metabolic cause. As with dogs, a low purine diet would be ideal, but there are no commercial veterinary therapeutic diets specifically formulated for cats. Purina HA and Royal Canin HP are lower in purine without a significant protein restriction. Low-protein diets like those for treatment of kidney disease are often used instead, and efforts at maintaining a more neutral to basic urine pH can be made since urate is less soluble in acidic urine.
A rise in cystine urolithiasis cases
During the past 10 to 15 years, we’ve observed a significant increase in the number of cystine urolithiasis cases. It is suspected that this is caused by the emergence of an androgen-dependent mutation in some large breed intact males that leads to increased cystinuria. Although dogs can be tested for this mutation, neutering of all intact males is recommended to prevent passage of any abnormalities to offspring.8 Cystine is an essential amino acid, so a diet containing cystine and its precursor methionine near AAFCO minimum levels is advised.11 Alkalization of the urine is also recommended due to the high solubility of cystine in basic urine. Limiting high sodium diets is recommended since some studies have shown that increased sodium intake increases cystine excretion in the urine. If nutritional management is unsuccessful, oral 2-mercaptopropionylglycine (2-MPG) may be tried. This drug complexes with cystine and has been used to dissolve and prevent uroliths. Although cystine urolithiasis in cats is very rare, avoidance of these amino acids and a low protein diet may also be advised.11
The most important nutritional aspect of managing urolithiasis of any type is water intake and dilution of the urine. Several urine-specific gravity targets have been suggested, with the most recent being less than 1.020 in dogs and less than 1.030 in cats.8 A diet of canned food, watering down of dry diets, and placement of fountains or other hydration devices in the animal’s environment are important ways to achieve this goal.
Although urate and cystine crystals may indicate a dog or cat is prone to develop those types of uroliths, the same is not true for struvite or calcium oxalate crystals. These can be found in concentrated urine of varying pH levels in animals that will never form uroliths. Unless the patient is already known to form uroliths, their presence does not indicate a need to place the patient on a special diet. In those patients that get urolithiasis, their presence indicates a need for additional prevention measures.
Nutrition plays a crucial role in managing urolithiasis in dogs and cats. Veterinary therapeutic diets have been specifically formulated for the management of several types of urolithiasis. If a patient will not consume the recommended diet, consider a consultation with a board- certified veterinary nutritionist for alternatives.
- Suby HI and Suby RM. Experimental production of kidney stones with urea-splitting organisms. J Urol. 1947;57(6):995-1000. doi:10.1016/ s0022-5347(17)69734-9.
- Abdullahi SU, Osborne CA, Leininger JR, Fletcher TF, Griffith DP. Evaluation of a calculolytic diet in female dogs with induced struvite urolithiasis. Am J Vet Res. 1984;45(8):1508-1519.
- Osborne CA, Klausner JS, Krawiec DR, Griffith DP. Canine struvite urolithiasis: problems and their dissolution. J Am Vet Med Assoc. 1981;179(3):239-244.
- Kopecny L, Palm CA, Segev G, Larsen JA, Westropp JL. Urolithiasis in cats: evaluation of trends in urolith composition and risk factors (2005-2018). J Vet Intern Med. 2021;35(3):1397-1405. doi: 10.1111/ jvim.16121.
- Lulich JP, Kruger JM, Macleay JM, Merrills JM, Paetau-Robinson I, Albasan H, et al. Efficacy of two commercially available, low-magnesium, urine-acidifying dry foods for the dissolution of struvite uroliths in cats. J Am Vet Med Assoc. 2013;243(8):1147-1153. doi: 10.2460/javma.243.8.1147.
- Tefft KM, Byron JK, Hostnik ET, Daristotle L, Carmella V, Frantz NZ. Effect of a struvite dissolution diet in cats with naturally occurring struvite urolithiasis. J Feline Med Surg. 2021;23(4):269-277. doi: 10.1177/1098612X20942382.
- Bartges JW, Kirk CA, Cox SK, Moyers TD. Influence of acidifying or alkalinizing diets on bone mineral density and urine relative supersaturation with calcium oxalate and struvite in healthy cats. Am J Vet Res. 2013;74(10):1347-1352. doi: 10.2460/ajvr.74.10.1347.
- Lulich JP, Berent AC, Adams LG, Westropp JL, Bartges JW, Osborne CA. ACVIM small animal consensus recommendations on the treatment and prevention of uroliths in dogs and cats. J Vet Intern Med. 2016;30(5):1564-1574. doi: 10.1111/ jvim.14559.
- Bijsmans E, Queau Y, Biourge V. Increasing dietary potassium chloride promotes urine dilution and decreases calcium oxalate relative supersaturation in healthy dogs and cats. Animals (Basel). 2021;11(6):18909. doi:10.3390/ani11061809.
- Queau Y, Bijsmans ES, Feugier A, Biourge VC. Increasing dietary sodium chloride promotes urine dilution and decreases struvite and calcium oxalate relative supersaturation in healthy dogs and cats. J Anim Physiol Anim Nutr (Berl). 2020;104(5):1524-1530. doi: 10.1111/jpn.13329.
- Queau Y. Nutritional management of urolithiasis. Vet Clin North Am Small Anim Pract. 2019;49(2):175-186. doi: 10.1016/j.cvsm.2018.10.004.