In 2021, 81 samples of stones were collected from the urinary tracts of dogs and cats in the UAE. These were submitted to the Canadian Veterinary Urolith Centre (CVUC). The CVUC is a collaboration between the University of Guelph Laboratory services and Royal Canin and opened in 1998.
The results from urolith analyses submitted from our UAE clinics have been collated and compared to global prevalence as described in the papers by Houston and Moore [1-3]. Here, the authors examined 50,000 submissions to the CVUC over a 10-year period from 1998- 2008 , and subsequently published species-specific findings [2, 3] in 2016 and 2017.
Here at SV Animal Health, we wanted to know how our regional results compared to the global trends seen in pets. For comparison, the same classifications as given in the papers were used to categorise our urolith submission results; a urolith is classified as ‘mixed’ when it contains more than one mineral, none of which compose more than 70% of the total composition. Otherwise, the stone is classified as the mineral that comprises >70% of the composition.
Definite global trends in each species based on breed and gender were described by CVUC . In both cats and dogs, struvite and calcium oxalate were the most common stones found, and over 85% of submissions were determined to have one of these two types of stone. In the UAE, struvite and calcium oxalate submissions accounted for 84% of the total samples, with ‘mixed’ uroliths contributing another 5%.
Of the 81 samples collected in 2021, 40 were from dogs. During the ten-year period, the CVUC found the global prevalence of calcium oxalate increased and the prevalence of struvite decreased in dogs . Much of this was attributed to the rise in the use of acidifying diets- making it easier and more effective to medically dissolve struvite crystals and stones, particularly in dogs . Also advances in the diagnosis of urinary tract infections means effective and prompt treatment is more readily available, and again this should lower the incidence of struvite formation . In 2020 in UAE, 35% of canine stones were found to be struvite, decreasing to 25% in 2021.
In dogs, struvite formation occurs in the presence of a urinary tract infection- which is suspected to be the reason that females outnumber males in canine struvite cases . Significant gender variation was seen at the CVUC, with females more likely to develop struvite stones and in males, calcium oxalate [1, 3].
This male predisposition has also been recognised in humans with calcium oxalate urolithiasis and a link to obesity has been hypothesized . A body condition score from the referring veterinarian could be an addition to future submission forms . In 2020, in the UAE, 100% of the calcium oxalate samples were from male dogs, and 76% of struvite samples were from female dogs. During the 2021 period we did not have data regarding the sex of patient.
Small breed dogs continued to be over-represented; with Pomeranians, Shih Tzus, French Bulldogs, Maltese, Cavalier Spaniels and Yorkshire Terriers now comprising 62% of total canine submissions from UAE (small breeds accounted for 50% in 2020, but the breeds seen were different). This is thought to be due to a combination of increasing popularity of these breeds and lifestyle factors associated with owning a smaller breed of dog; a more sedentary lifestyle and lower volumes of more concentrated urine voided less frequently, which has been observed in Miniature Schnauzers compared to Labradors . In the UAE, our pets have definite lifestyle alterations, particularly over the summer months, which may lead to disruptions in natural micturition habits. Further investigation into how this affects mineral composition and concentration of urine would be extremely interesting.
Our regional results suggest a slightly higher proportion of cystine stones compared to global trends (see Fig 2). Globally, cystine stones compose 0.6% of submissions , compared with 3% of UAE dog submissions (1 case). Cystine stones form because of a hereditary renal defect. With this defect, certain amino acids are not reabsorbed as they should be. Increased levels of cystine, ornithine, lysine and arginine in the urine will lead to an increase in crystal and stone formation in neutral to acidic urine. There are several breeds predisposed to cystine formation including Basenjis, English and French Bulldogs, Chihuahuas, and Labradors. In our regional results, the one cystine stone came from a Pomeranian. It is strongly suspected that a genetic link is significant and that screening and selective breeding will be fundamental in reducing the cases in the future .
Ammonium urate stones are the third most common type of stones seen at the CVUC contributing 3.2% of canine submissions. UAE results somewhat higher, with urate accounting for 8% of canine submissions. Urate stones in dogs are most commonly found in Dalmatians, due to an identified genetic mutation in uric acid metabolism. This mutation has also been identified in other breeds including Giant Schnauzers and Jack Russell Terriers. Urate stones can also be found in cases of liver failure, due to reduction in hepatic conversion of ammonia to urea, or uric acid to allantoin. In particular, patients with portosystemic shunts and hepatic cirrhosis are at risk of developing urate stones. The one sample collected from a Dalmatian in 2021 in UAE was urate. None of the other urate samples we collected were from the other breeds described above.
Of the 81 samples received from the UAE, 41 were from cats. 90% of feline samples were determined to be struvite or calcium oxalate, exactly mirroring the global results. The third most common stone found to be calcium phosphate.
The CVUC have noted a decrease in struvite submissions in the feline population similar to the canine, hypothesized to be due to better nutritional management options [1,2]. In 2020, 34% of feline stones were struvite, decreasing to 29% in 2021.
In the UAE in 2020, 75% of struvite samples were submitted from female cats, which follow global trends, although the association with bacterial infection is not a feature of feline struvite formation. The reason why female cats are more prone to struvite development is not currently known . Gender was not recorded in the 2021 UAE results.
Calcium oxalate has been the most common urolith submission worldwide since 2006 . In the UAE, a greater number of submissions came from purebred cats compared to domestic breeds, in particular Persians. This is likely a reflection of their popularity in this region. The CVUC noted that calcium oxalate stones are more likely to form in Persians, both male and female . This was certainly the trend found in the regional results also, with 60% of samples from Persians determined to be calcium oxalate. The theory of this breed being prone to idiopathic hypercalcaemia is not substantiated at this time and is an ongoing area of research .
Ammonium urate stones are more commonly found in the Egyptian Mau, Birman and Siamese breeds . Of the 4 Maus included in 2021, none had urate stones. With canine cases, a genetic cause has been determined in Dalmatians, but as yet, a similar explanation for the formation in cats has yet to be investigated .
Given the sample size from the region, these comparisons are only of interest rather than clinically significant. Also, only submissions from 2020 and 2021 have been analyzed currently- but collection of data is constant and re-evaluation planned for the future. Monitoring trends with age, gender and body condition score may be of added interest.
Despite generally following the trends seen in the CVUC, regionally we observe exceptions- and see value in continuing to consolidate and evaluate the results. SV Animal Health will continue to monitor the submissions beyond 2022, relying on our clinics providing the samples and entrusting us to ensure reliable and efficient analyses.
We offer the service as complimentary to all our customers- our delivery team can collect the samples and the courier to Canada is arranged several times a month and results normally take 3-4 weeks. Results include full nutritional recommendations with regards to the Royal Canin Veterinary Health Nutrition Range, and further support on a case-by-case basis if required. If you have not submitted a sample before, please contact firstname.lastname@example.org or email@example.com for the submission form and any general queries.
Written on March 15, 2022