WHAT ARE THE URINARY CALCULI ENCOUNTERED IN DOGS ?

It is less common to observe urinary calculi (or urolithiasis) in dogs than in cats. But when it happens, the clinical signs are the same. It is characterized by frequent and painful urination. Urine analysis often shows blood and crystals in the urine.

Contrary to the cat, the appearance of urinary calculi is frequently related to a urinary infection. Bacteria involved are not always found through simple urine analysis. The surest way to find them is to perform a biopsy from the bladder and to realize a culture with this sample. The most common responsible bacteria are: staphylococcus, Escherichia coli or streptococcus.

When the infection is confirmed, it is very likely that the urolithiasis is due to struvite calculi: because infection makes the urinary pH rise, and struvite crytals precipitate only in alcaline urine. Other type of urolithiasis rather appear in acid urine.

>From 1984 to 1996, a european study applied itself to classify the different types of urolithiasis, according to their frequency of observation:

• about 60 % of urolithiasis cases were represented by struvite
• cystine and oxalate calculi represented each about 15 % of cases. According to the different authors, the respective percentages can vary. Anyway, oxalate calculi seem to emerge more and more often, just as in cats;
• less than 10 % of urolithiasis are due to urate calculi.

Predisposing factors

Age
Urolithiasis is mainly encountered in 5 to 7 years old dogs.

Breed
In Davis University (CA), 11000 cases of canine urolithiasis have been studied between 1981 and 1994. From these data, the breed factor appears to be predominant. Out of 45 breeds represented in the study, 7-8 breeds gathered 70 % of affected males and 80 % of affected females.

• “ Risky dogs ” are usually small-breeds ones: English Bulldog, Poodle, Pug, Lhassa Apso, Pekinese, miniature Schnauzer, Shih Tzu, Daschund, Yorkshire, Welsh corgi, Westie…
• In the Dalmatian, a genetic defect is sometimes responsible for the lack of uric acid transformation into urea, leading to the appearance of urate calculi.
• In some lines of Newfoundlands, there is a predisposition for suffering from cystine calculi. This disease is transmitted hereditarily. It is due to an impaired renal reabsorption of some essential amino-acids, including cystine.

  Type of encountered calculi “ Risky breeds ” oxalate Lhassa Apso, Pug cystine English Bulldog, Newfoundland urate Dalmatian, English Bulldog, Basset Hound

• German shepherd, Labrador, Golden retriever, German Pointer and Sharpei are rarely concerned by urolithiasis.

Sex Males are affected twice often as females are. This is even more obvious for urate calculi in Basset Hound, English Bulldog and moreover Dalmatian, as 92 % of affected animals are males.

94 % of cases observed in females are due to struvite calculi, whereas the nature of calculi varies more in males. This can be connected with the fact that there are more urinary infections in females.

Medical and dietetic treatment

Just like in cats, fighting against calculi formation means that one must act on the urinary pH.

• In case of struvite urolithiasis, the treatment of the infection makes the urinary pH drop, and this is usually enough to stop the crystals precipitation.
• On the contrary, in all other cases, a urinary alcalinization is necessary.

Urate urolithiasis
Urate calculi formation is favorized by a urinary pH inferior to 6. Prevention consists in alcalinizing urine in order to go back up to a pH included between 6 and 7. A proteic restriction can be proposed, but the most important fact is to supply highly digestible proteins that do not encourage intestinal fermentation. Then ammonium production is reduced so as uric acid formation. There is also a drug, allopurinol, that limits uric acid formation.

Conclusion

When faced to a case of canine urolithiasis, the veterinarian has to identify which one it is, because the treatment and the dietary advice vary according the type of calculi involved. In case of struvite urolithiasis in a small dog, an acidifying catfood product can eventually be advised. The other solution is to add an acidifyer to the diet. In any other case, the Royal Canin product Canistar S3, can be prescribed because it helps fighting against acidosis.

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