Fasting urinary calcium-to-creatinine and oxalate-to-creatinine ratios in dogs with calcium oxalate urolithiasis and breed-matched controls

Clustering analysis of lipoprotein profiles to identify subtypes of hypertriglyceridemia in Miniature Schnauzers

BACKGROUND

Hypertriglyceridemia (HTG) is prevalent in Miniature Schnauzers, predisposing them to life-threatening diseases. Varied responses to management strategies suggest the possibility of multiple subtypes.

HYPOTHESIS/OBJECTIVE

To identify and characterize HTG subtypes in Miniature Schnauzers through cluster analysis of lipoprotein profiles. We hypothesize that multiple phenotypes of primary HTG exist in this breed.

ANIMALS

Twenty Miniature Schnauzers with normal serum triglyceride concentration (NTG), 25 with primary HTG, and 5 with secondary HTG.

METHODS

Cross-sectional study using archived samples. Lipoprotein profiles, generated using continuous lipoprotein density profiling, were clustered with hierarchical cluster analysis. Clinical data (age, sex, body condition score, and dietary fat content) was compared between clusters.

RESULTS

Six clusters were identified. Dogs with primary HTG were dispersed among 4 clusters. One cluster showed the highest intensities for triglyceride-rich lipoprotein (TRL) and low-density lipoprotein (LDL) fractions and also included 4 dogs with secondary HTG. Two clusters had moderately high TRL fraction intensities and low-to-intermediate LDL intensities. The fourth cluster had high LDL but variable TRL fraction intensities with equal numbers of NTG and mild HTG dogs. The final 2 clusters comprised only NTG dogs with low TRL intensities and low-to-intermediate LDL intensities. The clusters did not appear to be driven by differences in the clinical data.

CONCLUSIONS AND CLINICAL IMPORTANCE

The results of this study support a spectrum of lipoprotein phenotypes within Miniature Schnauzers that cannot be predicted by triglyceride concentration alone. Lipoprotein profiling might be useful to determine if subtypes have different origins, clinical consequences, and response to treatment.

Sequence Analysis of Six Candidate Genes in Miniature Schnauzers with Primary Hypertriglyceridemia

Miniature Schnauzers are predisposed to primary hypertriglyceridemia (HTG). In this study, we performed whole genome sequencing (WGS) of eight Miniature Schnauzers with primary HTG and screened for risk variants in six HTG candidate genes: LPL, APOC2, APOA5, GPIHBP1, LMF1, and APOE. Variants were filtered to identify those present in ≥2 Miniature Schnauzers with primary HTG and uncommon (<10% allele frequency) in a WGS variant database including 613 dogs from 61 other breeds. Three variants passed filtering: an APOE TATA box deletion, an LMF1 intronic SNP, and a GPIHBP1 missense variant. The APOE and GPIHBP1 variants were genotyped in a cohort of 108 Miniature Schnauzers, including 68 with primary HTG and 40 controls. A multivariable regression model, including age and sex, did not identify an effect of APOE (estimate = 0.18, std. error = 0.14; p = 0.20) or GPIHBP1 genotypes (estimate = -0.26, std. error = 0.42; p = 0.54) on triglyceride concentration. In conclusion, we did not identify a monogenic cause for primary HTG in Miniature Schnauzers in the six genes evaluated. However, if HTG in Miniature Schnauzers is a complex disease resulting from the cumulative effects of multiple variants and environment, the identified variants cannot be ruled out as contributing factors.

Trends in urolith composition and factors associated with different urolith types in dogs from the Republic of Ireland and Northern Ireland between 2010 and 2020

OBJECTIVES

The purpose of this study was to determine changes in urolith trends and factors associated with different urolith types in dogs from the Republic of Ireland and Northern Ireland between 2010 and 2020.

MATERIALS AND METHODS

A laboratory database was searched for canine urolith submissions between 2010 and 2020. Trends in urolith composition between 2014 and 2020, and associations between patient characteristics with each urolith type were evaluated.

RESULTS

A total of 1162 submissions were included. Struvite (39.0%), calcium oxalate (27.8%) and compound (10.2%) were the most prevalent uroliths. Calcium oxalate urolith (CaOx) incidence significantly increased from 27.8% to 31.2% and that of struvite significantly decreased from 41.7% to 33.0% between 2014 and 2020. Struvite uroliths were overrepresented among females compared to males (odds ratio 8.7, 95% confidence interval 6.6 to 11.5). Males (odds ratio 9.6, 95% confidence interval 6.9 to 13.3) and dogs >7 years of age (odds ratio 4.1, 95%, confidence interval 3.0 to 5.4) were more likely to have CaOx while males (odds ratio 9.6, 95% confidence interval 5.3 to 17.8) and dogs ≤7 year of age, purine uroliths (odds ratio 3.0, 95% confidence interval 1.8 to 5.0). Incidence was higher in bichon frise (odds ratio 1.7, 95% confidence interval 1.3 to 2.4) and Yorkshire terrier (odds ratio 2.8, 95% confidence interval 1.9 to 4.1) for CaOx and higher in shih-tzu for compound uroliths (odds ratio 1.7, 95% confidence interval 1.1 to 2.7) compared to the remaining reported breeds.

CLINICAL SIGNIFICANCE

Factors associated with different uroliths were similar to the ones previously reported. Proportion of CaOx submissions increased and that of struvite decreased over the study period which was in agreement with the changes identified in other European countries.

A urinary proteomic study in hypercalciuric dogs with and without calcium oxalate urolithiasis

Background and Aims

Hypercalciuria is an important predisposing factor commonly found in humans and dogs with calcium oxalate (CaOx) urolithiasis. Calcium oxalate crystals can induce an inflammatory reaction that subsequently produces several proteins that have an inhibitory or stimulatory effect on stone formation. This study aimed to evaluate the differences in urinary proteomic profiles between hypercalciuric CaOx stone dogs and hypercalciuric stone-free dogs (CaOx stone and control groups, respectively).

Materials and Methods

Seven dogs with hypercalciuric CaOx urolithiasis and breed-, sex-, and aged-matched controls with hypercalciuria were included in the study. Serum and urine samples were obtained from all dogs to analyze electrolytes. Urinary proteomic profiles were analyzed using liquid chromatography-mass spectrometry. Student's t-test was used to compare the differences between groups.

Results

Forty-nine urinary proteins were identified in the stone-free and CaOx stone groups, whereas 19 and 6 proteins were unique in the CaOx stone and stone-free groups, respectively. The urinary thrombomodulin level was significantly higher in the CaOx stone group (relative ratio = 1.8, p < 0.01) than in the stone-free group.

Conclusion

This study demonstrated that urinary proteomic profiles may be used as a candidate biomarker for urinary tract injury in CaOx urolithiasis in dogs.

Characterization of the urogenital microbiome in Miniature Schnauzers with and without calcium oxalate urolithiasis

Background

Calcium oxalate (CaOx) uroliths are common in dogs. Humans with CaOx urolithiasis exhibit alterations of the urinary and urogenital microbiomes that might mediate urolith formation. Detection of urogenital microbes associated with CaOx in dogs could inform disease pathophysiology.

Objective

To identify compositional differences in the urogenital microbiome of Miniature Schnauzers with and without CaOx uroliths.

Animals

Nineteen midstream, voided urine samples from Miniature Schnauzers with (n = 9) and without (n = 10) a history of CaOx urolithiasis.

Methods

Analytical cross‐sectional study. Microbial DNA was extracted from previously frozen urine samples and sequenced for the bacterial 16S rRNA V3‐V4 hypervariable regions. Diversity and composition of microbial populations were compared between urolith formers and controls.

Results

Alpha and beta diversity measures were similar between groups. Five individual bacterial taxa differed in abundance (indicator values >0.5 and P < .05): Acinetobacter, 2 Geobacillus variants, and Hydrogenophaga were overrepresented in the urine of urolith formers, and Sphingopyxis was overrepresented in controls. Two distinct subtypes of urine microbial composition were observed based on beta diversity measures, independent of urolith status, and other clinical variables.

Conclusions and Clinical Importance

Although we did not detect a difference in the overall urogenital microbial composition between groups, observed differences in individual bacterial taxa might be clinically relevant. For example, Acinetobacter was overrepresented in urolith formers and is associated with CaOx urolithiasis in humans. Two unique clusters of the microbiome were identified, independent of urolith status, which may represent distinct urotypes present in Miniature Schnauzers.

Upper urolithiasis in cats with chronic kidney disease: prevalence and investigation of serum and urinary calcium concentrations

OBJECTIVES

This study aimed to define the prevalence of upper urolithiasis in cats with chronic kidney disease (CKD) in a referral population, and to compare urinary calcium:creatinine ratio (UCa:Cr), and total and ionised calcium between cats with CKD with and without upper urolithiasis.

METHODS

The medical records of cats diagnosed with CKD were reviewed for signalment, body weight, diet and prevalence of upper urolithiasis. Cats with preserved urine samples were further classified into two groups: urolithiasis group (upper urolithiasis identified by abdominal ultrasonography) and control group (CKD of unknown origin). Serum biochemical analysis, CKD stage, blood gas analysis, urine specific gravity and UCa:Cr were compared between groups using a two-sample t-test or Mann-Whitney U-test for continuous variable and a χ2 test or Fisher's exact test for categorical variables. Multivariable binary logistic regression analysis was used to identify risk factors.

RESULTS

Among the 140 cats with CKD, the prevalence of upper urolithiasis was 73%. Fifty cats (5, 29 and 16 cats with CKD stages 1, 2 and 3, respectively) with urine samples met the inclusion criteria and were included in the analysis. Among cats with CKD, being purebred (odds ratio [OR] = 81.56; P = 0.03) and being fed dry food only (OR = 25.06; P = 0.001) were identified as independent upper urolithiasis risk factors; those with upper urolithiasis were more likely to be exclusively fed with urine-acidifying food (P <0.001) and have increased serum ionised calcium (iCa) (P = 0.044), fractional excretion of calcium (P = 0.45) and UCa:Cr (P = 0.005) than cats with CKD without upper urolithiasis.

CONCLUSIONS AND RELEVANCE

Cats with CKD that were purebred, fed dry food and fed urine-acidifying food only often had upper urolithiasis. A higher UCa:Cr may be a result of increased serum iCa and may cause upper urolithiasis.

NO PROGRESSION OF UROLITHS IN ASIAN SMALL-CLAWED OTTERS (AONYX CINEREUS) FED A NATURALISTIC CRUSTACEAN-BASED DIET FOR 2 YEARS

Asian small-clawed otters (ASCO; Aonyx cinereus) are a popular species of otter housed in zoological institutions. A common health challenge in this species is the development of uroliths, which may have a dietary origin. Feeding recommendations for ASCO are largely based on the nutrient requirements of domestic carnivore models. Using otter-specific feeding ecology may allow for further refinement of these nutrient recommendations. This study aimed to assess if a naturalistic diet of crustaceans, mollusks, and fish could control the development of uroliths in ASCO. Baseline data were collected on 10 ASCO (five males and five females) of different ages and repeated 2 years after the treatment diet was introduced. Blood and urine parameters, as well as the size of nephroliths based on radiographic images, were recorded. The treatment diet was higher in protein and lower in calcium than the nontreatment diet and did not contain any kibble. During the 2-year treatment trial, blood globulin, glucose, and sodium increased and albumin decreased. Glucosuria and leukocyturia significantly decreased. There were no significant changes in urolith size over the 2 years, and animals without nephroliths at the beginning of the study remained urolith free. The development of nephroliths was significantly reduced during the treatment compared with the year prior. Although interpretation is limited by the methods used, a naturalist diet may have a beneficial impact in the development of uroliths in ASCO.

The association between single nucleotide polymorphism in vitamin D receptor and calcium oxalate urolithiasis in dogs

Background

Polymorphisms of the vitamin D receptor (VDR) are associated with calcium oxalate (CaOx) nephrolithiasis in humans.

Objectives

To investigate the association between VDR polymorphisms and susceptibility to CaOx urolithiasis in dogs.

Animals

Thirty‐five dogs with CaOx urolithiasis were compared with 40 stone‐free dogs.

Methods

This was a case‐control study. Two VDR gene polymorphisms (rs851998024 and rs852900542) were detected by specific TaqMan real‐time polymerase chain reaction assay, and their relationship with serum 1,25‐dihydroxyvitamin D, serum and urinary electrolyte concentrations was evaluated.

Results

The distribution of the rs852900542 polymorphism was significantly different between the case and the control dogs (x² = 6.369, P = .04). Dogs with a CC or CT genotype had an increased risk of CaOx stones than those with the TT genotype (odds ratio = 3.82, 95% confidence interval 1.04‐13.98). The CaOx dogs with the TT genotype had a significantly lower urinary calcium‐to‐creatinine ratio than the CT+CC genotypes. 1,25‐(OH)2D concentrations did not differ between the cases and the controls (308.7 ± 217.4 vs 286.7 ± 185.1 pg/mL, P = .45).

Conclusions and Clinical Importance

This finding suggests that vitamin D metabolism might play a role in CaOx stone formation in dogs.

Increasing Dietary Potassium Chloride Promotes Urine Dilution and Decreases Calcium Oxalate Relative Supersaturation in Healthy Dogs and Cats

Urine dilution is a strategy used to decrease the risk of crystallization in cats and dogs at risk of urolithiasis. Sodium chloride has been used in prescription diets to effectively promote urine dilution, but the effect of the salt-substitute potassium chloride (KCl) on urine parameters has not been extensively investigated. Two diets differing only in KCl (Diet A; K 0.44 g/MJ, Diet B; K 1.03 g/MJ) were fed to 17 cats and 22 dogs for seven days, followed by three days of urine collection. Urinary ion concentrations were determined by ionic chromatography, and SUPERSAT software was used to calculate the relative supersaturation (RSS) value for struvite and calcium oxalate. Water intake and urine volume increased, and USG decreased on diet B (p < 0.001). Urine concentration of potassium increased on diet B, but concentrations of all other ions did not change or decrease in line with urine dilution. Calcium oxalate RSS decreased on diet B (p < 0.05). This short-term study showed that increased dietary KCl in a dry extruded diet effectively dilutes the urine of cats and dogs and therefore offers a novel nutritional strategy for the prevention of urolithiasis. This finding is of interest for patients that would benefit from dietary sodium restriction.

No Observed Adverse Effects on Health Were Detected in Adult Beagle Dogs When Fed a High-Calcium Diet for 40 Weeks

Simple Summary

Calcium (Ca) is an essential mineral that plays a vital role in many bodily functions. There is evidence that high levels of dietary Ca for puppies and growing dogs can result in adverse growth and health effects, with certain breeds and dog size categories being most susceptible, for example, large breed sizes or beagles. Until recently, little was known about the health consequences of high Ca diets to adult dog, however, a study in the large sized breed Labrador retriever found no adverse health consequences when feeding diets containing levels of Ca near maximum levels set by pet food regulators (2.5 g per 100 g dry matter) for 40 weeks. This current study fed a similar high Ca diet to adult beagles, a medium sized breed for 40 weeks and monitored the dogs’ health using an extensive suite of health parameters. All dogs remained healthy and did not display any clinically relevant signs of adverse health relating to diet at any point during or following completion of the study.

Abstract

The implications of long-term high calcium (Ca) intake are well documented in growing dogs and in adult dogs of large breed size, however, the consequences on other breeds and breed sizes are yet to be determined. Eighteen neutered adult beagles, nine males and nine females aged 1.4–4.4 years, were randomized to control or test diets providing in g∙4184 kJ⁻¹ (1000 kcal⁻¹): 1.44 and 7.19 total Ca balanced with 1.05 and 4.25 total phosphorus, respectively, for 40 weeks. Health parameters, ultrasound scans, radiographs, glomerular filtration rate, and mineral balance were measured at eight-week intervals. All dogs remained healthy with no measured evidence of orthopedic, urinary, or renal disease. The test diet resulted in a 5.2 fold increase in fecal Ca excretion. Apparent Ca digestibility (%) and Ca balance (g/d) did not significantly (p > 0.05) change from baseline in the test diet group, although dogs displayed a positive Ca balance (maximum at week 8, 1.11 g/d with 95% CI (0.41, 1.80)) before a neutral Ca balance was restored at week 32. Despite an initial positive Ca balance, we can conclude that no measurable adverse health effects were observed as a result of the test diet fed in this study in beagles over a period of 40 weeks.

Urolithiasis in dogs: Evaluation of trends in urolith composition and risk factors (2006-2018)

BACKGROUND

Urolithiasis is a common and often recurrent problem in dogs.

OBJECTIVE

To evaluate trends in urolith composition in dogs and to assess risk factors for urolithiasis, including age, breed, sex, neuter status, urolith location, and bacterial urolith cultures.

SAMPLE POPULATION

A total of 10 444 uroliths and the dogs from which they were obtained.

METHODS

The laboratory database at the UC Davis Gerald V. Ling Urinary Stone Analysis Laboratory was searched for all urolith submissions from dogs between January 2006 and December 2018. Mineral type, age, breed, sex, neuter status, urolith location, and urolith culture were recorded. Trends were evaluated and variables compared to evaluate risk factors.

RESULTS

Calcium oxalate (CaOx) and struvite-containing uroliths comprised the majority of all submissions from dogs, representing 47.0% and 43.6%, respectively. The proportion of CaOx-containing uroliths significantly decreased from 49.5% in 2006 to 41.8% in 2018 (P = .006), with no change in the proportion of struvite-containing urolith submissions. Cystine-containing uroliths comprised 2.7% of all submissions between 2006 and 2018 and a significant nonlinear increase in this mineral type occurred over time (1.4% of all submissions in 2006 to 8.7% in 2018; P < .001). Of all cystine-containing uroliths, 70.3% were from intact male dogs. Age, breed, and sex predispositions for uroliths were similar to those previously identified.

CONCLUSIONS AND CLINICAL IMPORTANCE

Although calcium oxalate- and struvite-containing uroliths continue to be the most common uroliths submitted from dogs, a decrease in the proportion of CaOx-containing uroliths and an increase in the proportion of cystine-containing uroliths occurred during the time period evaluated.

Calcium, Phosphorus, and Vitamin D in Dogs and Cats: Beyond the Bones

Calcium, phosphorus, and vitamin D are nutrients that play a key role in maintaining normal organ, cell, and tissue function. Much is known about their role in bone metabolism, but these nutrients are also important in renal health, urinary tract disease, and multiple other organ systems. It is nutritionally important to meet the physiologic requirements for each of these nutrients, but the interplay between them should also be considered.

Animal models of naturally occurring stone disease

The prevalence of urolithiasis in humans is increasing worldwide; however, non-surgical treatment and prevention options remain limited despite decades of investigation. Most existing laboratory animal models for urolithiasis rely on highly artificial methods of stone induction and, as a result, might not be fully applicable to the study of natural stone initiation and growth. Animal models that naturally and spontaneously form uroliths are an underused resource in the study of human stone disease and offer many potential opportunities for improving insight into stone pathogenesis. These models include domestic dogs and cats, as well as a variety of other captive and wild species, such as otters, dolphins and ferrets, that form calcium oxalate, struvite, uric acid, cystine and other stone types. Improved collaboration between urologists, basic scientists and veterinarians is warranted to further our understanding of how stones form and to consider possible new preventive and therapeutic treatment options.

Effects of calcifediol supplementation on markers of chronic kidney disease-mineral and bone disorder in dogs with chronic kidney disease

Background

Chronic kidney disease‐mineral and bone disorder (CKD‐MBD) in dogs is associated with hypovitaminosis D, increased parathyroid hormone (PTH), and increased fibroblast growth factor‐23 (FGF‐23) concentrations. Best practice for vitamin D metabolite supplementation in CKD‐MBD remains unknown.

Objective

To provide an extended‐release calcifediol supplement to dogs with CKD and to measure its effects on variables indicative of CKD‐MBD.

Animals

Ten dogs with International Renal Interest Society stages 2 and 3 CKD.

Methods

In a prospective study, dogs received a calcifediol supplement for 84 days. Serum 25‐hydroxyvitamin D (25[OH]D), 1,25‐dihydroxyvitamin D (1,25[OH]₂D), 24,25‐dihydroxyvitamin D (24,25[OH]₂D), creatinine, calcium, phosphorus, PTH, plasma FGF‐23 concentrations, and urine profiles were measured monthly during supplementation. Urine calcium to creatinine (UCa/Cr) ratios and fractional excretion of calcium, phosphorus, and sodium were determined.

Results

All serum vitamin D metabolite concentrations increased significantly by day 84 (P < .001): [25(OH)D (median 249.9 ng/mL; range, 149.7‐469.9 ng/mL) compared to baseline (median 50.2 ng/mL; range, 31.3‐66.0 ng/mL); 1,25(OH)₂D (median 66.1 pg/mL; range, 56.9‐88.1 pg/mL) compared to baseline (median 37.3 pg/mL; range, 29.3‐56.7 pg/mL); 24,25(OH)₂D (median 81.4 ng/mL; range, 22.1‐151.7 ng/mL) compared to baseline (median 15.4 ng/mL; range, 6.9‐40.6 ng/mL)]. There were no significant differences in calcium, phosphorus, PTH concentrations, UCa/Cr or fractional excretion of calcium. No dog developed ionized hypercalcemia. Plasma FGF‐23 concentrations increased by day 84 (median 1219 pg/mL; range, 229‐8824 pg/mL) compared to baseline (median 798 pg/mL; range, 103‐4.145 pg/mL) (P < .01).

Conclusions and Clinical Importance

Calcifediol supplementation for 84 days was well‐tolerated in dogs with IRIS stages 2 and 3 CKD. It remains to be determined how long‐term supplementation would affect CKD progression and QOL.

Measurement of preprandial and postprandial urine calcium to creatinine ratios in male Miniature Schnauzers with and without urolithiasis

Background

We aimed to identify a simple test for excessive calciuresis and predict calcium oxalate (CaOx) disease in Miniature Schnauzers. We investigated the impact of postprandial time on the urine calcium to creatinine ratio (UCa/Cr) in male dogs of this breed, with the goal of improving the utility of the UCa/Cr.

Hypotheses

(1) Significant differences will exist in preprandial and postprandial UCa/Cr between CaOx urolith‐forming and control Schnauzers. (2) The UCa/Cr will increase significantly from the first morning baseline at ≥1 postprandial time point(s) in both control and CaOx urolith‐forming dogs. (3) Biochemical abnormalities and other variables may be associated with urolith status.

Animals

Twenty‐four male Miniature Schnauzer dogs, consisting of 9 with (urolith formers) and 15 without (controls) CaOx uroliths.

Methods

Urine was collected before and 1, 2, 4, and 8 hours after feeding a standardized diet. Receiver operator characteristic curve analysis was performed to identify the UCa/Cr cutoff that most accurately differentiates dogs based on urolith status.

Results

Urolith formers had significantly higher mean UCa/Cr over the course of 8 hours. The postprandial change in UCa/Cr was not significant at any time point between or within groups. The cutoff UCa/Cr value of 0.06 had a specificity of 93% (95% confidence interval [CI], 80%‐100%) and a sensitivity of 56% (95% CI, 21%‐86%) for identifying CaOx urolithiasis.

Conclusions and Clinical Importance

Urolith‐forming male Miniature Schnauzers have excessive calciuresis, and the postprandial sampling time up to 8 hours is not critical. This simple urine measurement has potential as a marker of CaOx disease.

Urinary calcium assessment and its relation with age, sex and Encephalitozoon cuniculi serological status in otherwise healthy pet rabbits

BACKGROUND

Urinary calcium excretion by rabbits is set proportionately higher than that of other species, giving the rabbit urine its characteristic cloudy appearance. During pregnancy, lactation and growth, or when metabolic disorders interfere in the renal excretion of calcium, it is reported that less calcium is excreted and the urine appears clear. The quantification of the calcium concentration in the urine of rabbits may be of importance in the management of diseases that affect calcium metabolism, especially in kidney disease; however, reference intervals for urinary calcium concentration (UC) are unreported in pet rabbits.

METHODS

Prospective data from 63 healthy pet rabbits were evaluated. An inhouse modified Arsenazo III technique, without acidifying the urine, was used to determine the reference intervals for UC and UC:creatinine ratio. Urinary protein:creatinine ratio, UC, UC:creatinine ratio, urinary gamma-glutamyl transferase concentration (UG), UG:creatinine ratio, phosphorus, plasma total calcium, plasma creatinine, urea and ionised calcium were assessed according to age, sex, neutered status, urine collection method and Encephalitozoon cuniculi IgG status in healthy rabbits.

RESULTS

The reference intervals for UC and UC:creatinine ratio were 4.2-31.1 mg/dl (1.03-7.78 mmol/l) and less than 0.3, respectively. The results showed that none of these variables was influenced by the parameters evaluated, except for the phosphorus value, which was higher in pet rabbits aged up to 3 years compared with those over 3 years, suggesting that published reference values for plasma phosphorus in rabbits should be adjusted according to age.

CONCLUSION

The modified Arsenazo III technique described in the present work and the established reference values for UC and UCC in pet rabbits could be useful in the management of kidney disease in rabbits. The results showed that E cuniculi IgG seropositivity has no influence on the variables of renal interest in otherwise healthy rabbits.

Vitamin D metabolism in dogs with and without hypercalciuric calcium oxalate urolithiasis

Background

There are abnormalities in vitamin D metabolism in people with calcium nephrolithiasis, but limited data are available on vitamin D status in dogs with calcium oxalate (CaOx) urolithiasis.

Objective

To compare serum concentrations of vitamin D metabolites in dogs with and without hypercalciuric CaOx urolithiasis.

Animals

Thirty‐eight dogs with (n = 19) and without (n = 19) a history of CaOx urolithiasis and hypercalciuria.

Methods

Retrospective cross‐sectional study. Serum 25‐hydroxyvitamin D [25(OH)D], 1,25‐dihydroxyvitamin D [1,25(OH)₂D], and 24,25‐dihydroxyvitamin D [24,25(OH)₂D] were measured. The ratios of 25(OH)D/24,25(OH)₂D and 1,25(OH)₂D/25(OH)D were compared between cases and controls.

Results

There were no significant differences between cases and controls when comparing 25(OH)D, 24,25(OH)₂D, 1,25(OH)₂D, or 1,25(OH)₂D/25(OH)D. Cases had higher 25(OH)D/24,25(OH)₂D (median = 1.40, range = 0.98‐1.58) compared to controls (median = 1.16, range = 0.92‐2.75; P = .01). There was overlap in the ranges for 25(OH)D/24,25(OH)₂D between cases and controls, but 6 cases (32%) had ratios above the control dog range. There was a moderate positive correlation between the ratio of 25(OH)D/24,25(OH)₂D and urinary calcium‐to‐creatinine ratios (r = 0.40, 95% confidence interval = 0.10‐0.64; P = .01).

Conclusions and Clinical Importance

These data suggest that decreased conversion of 25(OH)D to 24,25(OH)₂D occurs in a subset of dogs with CaOx urolithiasis. Abnormalities in vitamin D metabolism might contribute to stone risk in dogs.

Bone resorption in dogs with calcium oxalate urolithiasis and idiopathic hypercalciuria

People with calcium oxalate (CaOx) urolithiasis and idiopathic hypercalciuria (IH) often have evidence of increased bone resorption, but bone turnover has not previously been investigated in dogs with these conditions. The aim of this study was to determine whether a marker of bone resorption, β-crosslaps, differs between dogs with CaOx urolithiasis and IH compared to controls. This retrospective, cross-sectional study used a canine specific ELISA to measure β-crosslaps concentrations in stored frozen serum samples from 20 dogs with CaOx urolithiasis and IH and 20 breed-, sex-, and age-matched stone-free controls (18 Miniature Schnauzers, 14 Bichons Frise, and 8 Shih Tzus). Dogs with CaOx urolithiasis and IH had lower β-crosslaps concentrations relative to controls (P = .0043), and β-crosslaps had a moderate negative correlation with urinary calcium-to-creatinine ratios (r = -0.44, P = .0044). Miniature Schnauzers had lower β-crosslaps concentrations than the other two breeds (P = .0035). The ELISA had acceptable intra-assay precision, but concentrations decreased when samples were repeatedly assayed over time. Assay recovery rates were also below acceptance criteria. In conclusion, Miniature Schnauzers, Bichons Frise, and Shih Tzus with CaOx urolithiasis and IH have evidence of decreased bone resorption compared to stone-free controls. This suggests that other causes of IH, such as intestinal hyperabsorption of calcium, underlie risk for CaOx urolithiasis in these breeds. Results should be confirmed in larger populations and with other β-crosslaps assays and additional biomarkers of bone turnover. The stability of canine serum β-crosslaps after freeze-thaw cycles and storage at various temperatures requires investigation.

Nutritional Management of Urolithiasis

Dietary management of urolithiasis in dogs and cats is designed to dissolve calculi when possible and/or reduce the risk of recurrence. The diet must reduce urine relative supersaturation for the particular salt in order to prevent crystallization. To decrease urinary concentrations of crystal precursors, increasing water intake is essential regardless of the stone type. Altering the amounts of dietary precursors of the stone and controlling urine pH is mostly effective for struvite, urate, xanthine, and cystine, but still subject to controversy for calcium oxalate. The investigation of underlying metabolic disorders and close monitoring of animals at risk is recommended.

Comparison of body condition score and urinalysis variables between dogs with and without calcium oxalate uroliths

OBJECTIVE To compare body condition score (BCS) and urinalysis variables between dogs with and without calcium oxalate (CaOx) uroliths. DESIGN Case-control study. ANIMALS 46 Miniature Schnauzers, 16 Bichons Frises, and 6 Shih Tzus. PROCEDURES Medical records were reviewed for Miniature Schnauzers, Bichons Frises, and Shih Tzus that were examined between January 2001 and November 2014 for another urolithiasis study or for a urolith removal procedure. Dogs with CaOx uroliths were classified as cases. Dogs without a history of urinary tract disease and with no evidence of radiopaque uroliths on abdominal radiographs were classified as controls. Each case was matched with 1 control on the basis of age (± 2 years), sex, and breed. Body condition score and urinalysis results were compared between cases and controls, and the relationship between BCS and urine pH was analyzed. RESULTS Median BCS was significantly greater for cases than controls, although the proportion of overweight dogs did not differ significantly between the 2 groups. Urine pH was negatively associated with age, but was not associated with BCS or the presence of CaOx uroliths. Cases infrequently had acidic urine or CaOx crystalluria but frequently had hematuria and proteinuria. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that dogs with CaOx uroliths had a greater median BCS than control dogs, but the clinical importance of that finding was unclear. Acidic urine and CaOx crystalluria were uncommon and not adequate predictors of CaOx urolith status. Hematuria and proteinuria were commonly observed in dogs with CaOx urolithiasis, but they are not pathognomonic for that condition.

Urinary metals in a spontaneous canine model of calcium oxalate urolithiasis

Calcium oxalate urolithiasis is a common and painful condition in people. The pathogenesis of this disease is complex and poorly understood. Laboratory animal and in vitro studies have demonstrated an effect of multiple trace metals in the crystallization process, and studies in humans have reported relationships between urinary metal concentrations and stone risk. Dogs are a spontaneous model of calcium oxalate urolithiasis, and the metal content of canine calcium oxalate stones mirrors that of human stones. The aim of this study was to test for a relationship between urinary metals and calcium oxalate urolithiasis in dogs. We hypothesized that urinary metals would differ between dogs with and without calcium oxalate urolithiasis. Urine from 122 dogs (71 cases and 51 stone-free controls) was analyzed for calcium and 12 other metals. The cases had higher urinary calcium, copper, iron, and vanadium and lower urinary cobalt. Higher urinary vanadium in the cases was associated with being fed a therapeutic stone-prevention diet. Urinary calcium had a strong positive correlation with strontium and moderate positive correlations with chromium, nickel, and zinc. The results of this study complement the findings of similar human studies and suggest a potential role of trace metals in calcium oxalate urolithiasis. Further investigation into how trace metals may affect stone formation is warranted.

Pathogenesis of calcium oxalate urinary stone disease: species comparison of humans, dogs, and cats

Idiopathic calcium oxalate nephrolithiasis is a highly recurrent disease that is increasing in prevalence. Decades of research have not identified effective methods to consistently prevent the formation of nephroliths or induce medical dissolution. Idiopathic calcium oxalate nephroliths form in association with renal papillary subepithelial calcium phosphate deposits called Randall's plaques (RPs). Rodent models are commonly used to experimentally induce calcium oxalate crystal and stone formation, but a rodent model that conclusively forms RPs has not been identified. Both dogs and cats form calcium oxalate uroliths that can be recurrent, but the etiopathologic mechanisms of stone formation, especially renal pathologic findings, are a relatively unexploited area of study. A large animal model that shares a similar environment to humans, along with a shorter lifespan and thus shorter time to recurrence, might provide an excellent means to study preventative and therapeutic measures, along with enhancing the concepts of the one health initiative. This review article summarizes and compares important known features of idiopathic calcium oxalate stone disease in humans, dogs, and cats, and emphasizes important knowledge gaps and areas for future study in the quest to discover a naturally occurring animal model of idiopathic calcium oxalate stone disease.

Elemental Content of Calcium Oxalate Stones from a Canine Model of Urinary Stone Disease

One of the most common types of urinary stones formed in humans and some other mammals is composed of calcium oxalate in ordered hydrated crystals. Many studies have reported a range of metals other than calcium in human stones, but few have looked at stones from animal models such as the dog. Therefore, we determined the elemental profile of canine calcium oxalate urinary stones and compared it to reported values from human stones. The content of 19 elements spanning 7-orders of magnitude was quantified in calcium oxalate stones from 53 dogs. The elemental profile of the canine stones was highly overlapping with human stones, indicating similar inorganic composition. Correlation and cluster analysis was then performed on the elemental profile from canine stones to evaluate associations between the elements and test for potential subgrouping based on elemental content. No correlations were observed with the most abundant metal calcium. However, magnesium and sulfur content correlated with the mineral hydration form, while phosphorous and zinc content correlated with the neuter status of the dog. Inter-elemental correlation analysis indicated strong associations between barium, phosphorous, and zinc content. Additionally, cluster analysis revealed subgroups within the stones that were also based primarily on barium, phosphorous, and zinc. These data support the use of the dog as a model to study the effects of trace metal homeostasis in urinary stone disease.