Genetic Welfare Problems of Companion Animals

An information resource for prospective pet owners

Miniature Schnauzer 

Miniature Schnauzer

Calcium Oxalate Urolithiasis

Related terms: crystalluria; Stones, bladder stones

VeNom term:  Urolithiasis/crystalluria - calcium oxalate (VeNom code: 2062)

Related conditions: hypercalciuria

Outline: Urolithiasis refers to the formation of stones anywhere within the urinary tract. Stones are named after the chemicals that combine to form them This page specifically describes calcium oxalate urolithiasis and does not refer to other types. Calcium oxalate stones are formed when calcium and oxalate ions combine. Miniature schnauzers have a greater risk of forming stones of calcium oxalate than other breeds of dogs. Such stones are more likely to develop when there are high concentrations of calcium and oxalic acid in the urine and when crystals of these chemicals travel slowly along the urinary tract. Urinary tract infection, diet and water intake, and the volume and frequency of urination can influence both these factors.

Stones can develop or reside anywhere in the urinary tract - in the kidney, bladder or urethra – and cause irritation, secondary infection or obstruction. Since they can irritate, inflame and/or damage the bladder or urethral walls stones may cause the affected animal pain, and dogs with stones are more prone to urinary tract infections. Dogs may experience pain when attempting to pass urine and blood in the urine may appear as a result of damage to the bladder or urethral walls.

The genetic mechanisms underlying the greater risk of stone formation in Miniature schnauzers are unknown but stone formation is more common in males than females. Miniature schnauzers may have qualities of urine production which make them more prone to stone formation, for example they produce a small, concentrated volume of urine and urinate less frequently.


Summary of Information

(for more information click on the links below)

1. Brief description

Urolithiasis is a condition in which mineral crystals in urine combine to form stones (also called uroliths, calculi or ‘Stones’). Stones are classified based on the type of minerals that they are composed of, and commonly are formed from any of 10 different minerals, either combined in various combinations or individually; calcium oxalate stones are formed when calcium and oxalate ions combine. These stones can develop or reside anywhere in the urinary tract - in the kidney, bladder or urethra – and their presence causes irritation and secondary infection. Most stones end up in the bladder or in the urethra, where they may cause obstruction.

The underlying causes of calcium oxalate urolith formation in Miniature schnauzers are unknown and it is thought to be a complex process. Such stones are more likely to develop when there are high concentrations of calcium and oxalic acid in the urine and when crystals of these chemicals travel slowly along the urinary tract. Urinary tract infection, diet and water intake, and the volume and frequency of urination can influence both these factors. Miniature schnauzers may be more likely to form such stones than other breeds as they are found to urinate less often and produce a smaller, more concentrated volume of urine containing more calcium. These factors could increase likelihood of crystallisation and subsequent crystal growth in Miniature schnauzers.

Stones may irritate, inflame and damage the bladder or urethral walls. Large or multiple stones may cause obstruction in the bladder or urinary tract and in severe cases, this may cause bladder rupture, which is a medical emergency with rapid veterinary treatment being necessary to save life.

2. Intensity of welfare impact   

Small stones may cause minimal adverse effect and are usually passed from the urinary tract during urination, without the need for intervention. However, even small stones can irritate, inflame and damage the bladder or urethral walls and thereby cause pain and the appearance of blood in the urine. Urinary tract infections are commonly associated with stones and are likely to cause persistent pain.

Multiple or large stones commonly cause obstruction to the urethra, the duct by which urine is passed out of the body, and lead to urine retention. Animals with urethral obstruction may attempt to urinate frequently but pass little urine and may experience extreme pain and distress (eg yelping) when urinating, which increases with the volume of urine of retained.  In severe obstruction, if appropriate treatment is not given promptly, the overfilled bladder may rupture, leading to infection and serious complications which could result in death within hours. Treatment often requires major surgery which has its own welfare implications.

3. Duration of welfare impact

Older dogs are more commonly affected by calcium oxalate stones, and they commonly reoccur in affected animals. Dietary management may reduce the risk of calcium oxalate urolith development. Removal of these stones often requires surgical intervention.

4. Number of animals affected

Calcium oxalate stones occur in smaller and toy breed dogs. Miniature schnauzers have a higher risk of developing calcium oxalate stones than other breeds.

Male dogs and overweight dogs also have an increased risk of developing calcium oxalate stones.

5. Diagnosis

Stones can be diagnosed with an x-ray or ultrasound scan of the urinary tract. Quantitative analysis of stones is recommended, eg via optical crystallography or infrared spectroscopy, to identify which minerals they contain.

6. Genetics

The genetic mechanisms of urolith development in Miniature schnauzers are not known, but it is suspected that some factors relating to calcium oxalate urolithiasis may be inherited in this breed.

7. How do you know if an animal is a carrier or likely to become affected?

Currently, it is not known which individual animals are more likely to become affected. We do know that Miniature schnauzers – especially males – are more at risk of developing calcium oxalate stones.

8. Methods and prospects for elimination of the problem

Since the genetic mechanisms for the development of calcium oxalate stones in Miniature schnauzers are unknown, the methods for elimination or reduction of the problem are limited.

Environmental factors, such as diet and exercise play an important role in reducing the risk of urolith development, even in breeds predisposed to the condition.


For further details about this condition, please click on the following:
(these link to items down this page)


1. Clinical and pathological effects

Urolithiasis is a condition in which mineral crystals in urine combine to form stones (also called uroliths or calculi). Stones can be composed of individual or combinations of approximately 10 different minerals, and stones are classified based on the type of minerals that form them. Calcium oxalate is a calcium salt of oxalic acid and forms when calcium and oxalate ions combine; they are one of the most common types of stones in dogs. Although there are different combinations of calcium oxalate salts, calcium oxalate stones are most commonly the monohydrate form (crystal name: whewellite) rather than the dihydrate form (weddellite) in dogs. Stones can develop or reside anywhere in the urinary tract - in the kidney, bladder or urethra – and commonly cause irritation and secondary infection. Most stones end up in the bladder or in the urethra, where they may cause obstruction.

The underlying causes of calcium oxalate stone formation in Miniature schnauzers are unknown and it is thought to be a complex process, involving numerous factors. High concentrations of calcium and oxalic acid in the urine and a slow passage of crystals of these minerals along the urinary tract contribute to stone formation. Normally, urine is of an acidity that means calcium and oxalic acid remain dissolved within it, but if the urine becomes less acidic or if there are high levels of these chemicals in the urine a threshold is reached,  and  crystals begin to spontaneously develop, clump together and grow (Bartges et al 1999). Stone formation can be accelerated by other factors such as urinary tract infection, high calcium diet, low water intake, and a decreased volume and frequency of urination. Excessive concentrations of calcium in the urine (hypercalciuria) can result from excessive dietary intake of calcium, impaired retention of calcium by the kidneys, and/or excessive calcium released from bones.

Stones may irritate, inflame and damage the bladder or urethral walls Dogs may have difficulties and pain when urinating and there may be blood in the urine (hematuria).

Affected dogs are prone to urinary tract infections, since stones can irritate the lining of the urinary tract, but it is not clear whether these infections are a primary cause of the urolithiasis or a secondary factor resulting from the urinary stones. Multiple or large stones may cause obstruction in the urinary tract and lead to urine retention. If the stones completely block the urethra (the tube from the bladder to outside) the affected dogs will show signs of increasing distress and frequently trying but failing to pass urine. These dogs may vomit, be anorexic (not want to eat) and have a tender abdomen. This is a medical emergency and if an animal is left for long in this state they can rapidly become very sick.  Within a few hours the overfilled bladder may rupture, leading to infection and inflammation of the stomach lining (peritonitis) and gut absorption of toxins and potassium from the urine. This can cause excessive levels of acid in the blood (metabolic acidosis) and extremely high levels of potassium in the blood (hyperkalemia), leading to cardiac arrest and death.

A study found several characteristics of urine production in Miniature schnauzers, which might explain the increased susceptibility to calcium oxalate stone formation in this breed. Differences in urine composition were found between Miniature schnauzers, a breed which are predisposed to develop calcium oxalate stones, and Labrador retrievers, a breed which rarely develop such stones. Miniature schnauzers urinated less frequently, and produced a smaller, more concentrated volume of urine than Labrador retrievers (Stevenson & Markwell 2005). The urine produced by Miniature schnauzers was also more alkaline and contained more calcium. These factors might increase the likelihood of crystallisation and subsequent crystal growth. Miniature schnauzers with calcium oxalate stones had higher levels of calcium and uric acid in their urine, compared to healthy controls of the same breed (Lulich et al 1991).

Dogs with hyperadrenocorticism (chronic overproduction of glucocorticoids; also known as Cushing’s disease) are considered to be more at risk of developing calcium oxalate stones (Hess et al 1998). This is because excess cortisol in the blood leads to increased levels of calcium which is excreted by the kidneys into the urine. 

Miniature schnauzers are also prone to developing another type of urolithiasis – struvite urolithiasis, in which, stones are primarily made up of magnesium, ammonium and phosphate. These types of stones are commonly associated with urinary tract infections (Osborne et al 1999).

 

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2. Intensity of welfare impact

Small stones may cause minimal adverse effect and may pass from the urinary tract, without the need for intervention, during normal urination. However, even small stones may still irritate, inflame and damage the bladder or urethral walls, and therefore affected dogs may have difficulties and pain when urinating. Urinary tract infections are commonly associated with stones and are likely to be painful; in one study, 46% of dogs with urolithiasis had urinary tract infections (Hesse 1990).

The pain and discomfort associated with inflammation of the urinary tract can last weeks and is unlikely to resolve without treatment, which often needs to be surgical. People affected by kidney or bladder stones report them as causing intense pain, especially if lodged in the urethra (the tube from the bladder to outside) and during urination. The pain increases in intensity as the bladder becomes fuller. Also, due to the associated secondary kidney failure affected individuals rapidly feel very ill, do not want to eat and start to vomit. Animals can die from a blocked urinary system within 24-48 hours without appropriate treatment. In cases of severe obstruction, the overfilled bladder may rupture, leading to infection, inflammation of the stomach lining (peritonitis) and gut absorption of toxins and potassium from the urine. This can cause excessive levels of acid in the blood (metabolic acidosis) and extremely high levels of potassium in the blood (hyperkalemia), leading to cardiac arrest and death.

Dogs with bladder stones and clinical signs usually need surgery to remove the stones. Surgical intervention and the invasive procedures necessary for emergency treatment of blockages may be stressful to animals and can in themselves cause distress, discomfort and pain.

 

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3. Duration of welfare impact

Older dogs are more commonly affected by calcium oxalate stones. According to Lulich et al (1999a)  60% of dogs with stones were between 6 and 11 years old, with an average age of 8.5 years. Reoccurrence of stones is common, and occurred in 50-60% of affected dogs within 3 years (Lulich et al 1993). Dietary management, for example, reduced calcium and sodium intake, may reduce the risk of calcium oxalate urolith development (Stevenson et al 2004).

Appropriate treatment of stones depends on the location of the urolith and its chemical composition, as well as on patient-specific factors, but it may include dietary and medical management (eg managing urinary tract infections) or surgical removal.

Smaller stones can be removed non-surgical by urohydropropulsion, where the stones are flushed out using a special urinary catheter technique whilst the dog is anesthetised. Larger stones are removed via surgery.  In a case series of surgical treatment of 16 dogs with stones, there was good  long-term survival in the majority of dogs examined (Snyder et al 2005). Four dogs died or were euthanised because of complications of kidney stones, such as an accumulation of nitrogen waste products in the blood (eg due to obstruction)..Return to top

4. Number of animals affected

Calcium oxalate stones are common in small and toy breed dogs (Stevenson & Markwell 2005); Miniature schnauzers in particular have a higher risk of developing calcium oxalate stones than other breeds. In Canada and United States, Miniature schnauzers were 14 times more likely to have calcium oxalate stones compared with mixed-breed dogs (95% confidence interval: 10.17-19.54; (Lekcharoensuk et al 2000).

Male dogs have an increased risk of calcium oxalate urolithiasis compared to females; approximately 70% of dogs with calcium oxalate stones submitted to the Canadian Veterinary Urolith Centre between 1998 and 2008 were from male dogs (Lulich et al 1999b). The explanation for this difference in dogs is unknown. One study showed that neutered male dogs had 14 times higher risk than sexually intact females (Lekcharoensuk et al 2000) and it is thought to be due to differences in the quality and quantity of urinary crystal aggregation and/or the protective effects of female hormones in decreasing urine calcium concentration.

Overweight dogs had 2 times greater risk for developing stones than dogs of ideal body weight (Lekcharoensuk et al 2000).

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5. Diagnosis

Stones can be diagnosed using radiography or ultrasonography of the bladder. Where there are lots of stones, or when stones are large, veterinarians may be able to physically feel the stones in the bladder.  

It is important to also identify the composition and structure of the stones at diagnosis, for effective treatment. Quantitative analysis of stones is recommended, eg via optical crystallography or infrared spectroscopy.

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6. Genetics

A predisposition to form calcium oxalate stones has been shown to be passed down to family members in humans (Goodman et al 1995) and rats (Bushinsky et al 1995), but to date, this has not been reported in dogs. Miniature schnauzers, as well as other small breeds, have a greater risk of developing calcium oxalate stones, and there are differences in urine production in healthy Miniature schnauzers compared with dogs in other breeds (Stevenson & Markwell 2005). These studies suggest that some factors relating to calcium oxalate urolithiasis may be inherited.

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7. How do you know if an animal is a carrier or likely to become affected?

It is currently not known which animals are more likely to become affected. We do know that the Miniature schnauzer breed is more at risk of developing calcium oxalate stones.

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8. Methods and prospects for elimination of the problem

Since the genetic mechanisms for the development of calcium oxalate stones in Miniature schnauzers are unknown, the methods for elimination of the problem are limited (Meyers-Wallen 2003). Environmental factors, such as diet and exercise play an important role in reducing the risk of urolith development, even in breeds predisposed to the condition.

The best advice that can be offered to prospective breeders is to avoid breeding between severely affected dogs or dogs with severely affected relatives including grandparents, siblings, previous offspring and siblings of parents.

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9. Acknowledgements

UFAW thanks Dr Emma Buckland (BSc, PhD), Dr David Brodbelt (MA VetMB PhD DVA DipECVAA MRCVS) and Dr Dan O’Neill (MVB BSc, MSc, PhD, MRCVS) for their work in compiling this section.

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10. References

Bartges JW, Osborne CA, Lulich JP, Kirk C, Allen TA and Brown C (1999) Methods for Evaluating Treatment of Uroliths. Veterinary Clinics of North America: Small Animal Practice 29: 45–57

Bushinsky DA, Grynpas MD, Nilsson EL, Nakagawa Y and Coe FL (1995) Stone formation in genetic hypercalciuric rats. Kidney International 48: 1705–1713

Goodman HO, Holmes RP and Assimos DG (1995) Genetic factors in calcium oxalate stone disease. The Journal Of Urology 153: 301–7

Hess RS, Kass PH and Ward CR (1998) Association between hyperadrenocorticism and development of calcium-containing uroliths in dogs with urolithiasis. Journal of the American Veterinary Medical Association 212: 1889–91

Hesse A (1990) Canine urolithiasis: epidemiology and analysis of urinary calculi. Journal of Small Animal Practice 31: 599–604

Lekcharoensuk C, Lulich JP, Osborne CA, Pusoonthornthum R, Allen TA, Koehler LA, Urlich LK, Carpenter KA and Swanson LL (2000) Patient and environmental factors associated with calcium oxalate urolithiasis in dogs. Journal of the American Veterinary Medical Association 217: 515–519

Ling G V, Thurmond MC, Choi YK, Franti CE, Ruby AL and Johnson DL (2003) Changes in proportion of canine urinary calculi composed of calcium oxalate or struvite in specimens analyzed from 1981 through 2001. Journal Of Veterinary Internal Medicine 17: 817–23

Lulich JP, Osborne CA, Nagode LA, Polzin DJ and Parke ML (1991) Evaluation of urine and serum metabolites in miniature schnauzers with calcium oxalate urolithiasis. American Journal Of Veterinary Research 52: 1583–90

Lulich JP, Osborne CA, Thumchai R, Lekcharoensuk C, Ulrich LK, Koehler LA, Bird KA, Swanson LL and Nakagawa Y (1999a) Epidemiology of canine calcium oxalate uroliths. Identifying risk factors. The Veterinary Clinics Of North America. Small Animal Practice 29: 113–22, xi

Lulich JP, Osborne CA, Thumchai R, Lekcharoensuk C, Ulrich LK, Koehler LA, Bird KA, Swanson LL and Nakagawa Y (1999b) Epidemiology of Canine Calcium Oxalate Uroliths. Veterinary Clinics of North America: Small Animal Practice 29: 113–122

Lulich JP, Perrine L, Osborne CA and Unger L (1993) Postsurgical recurrence of calcium oxalate uroliths in dogs. Journal of Veterinary Internal Medicine 203: 863–869

Meyers-Wallen VN (2003) Ethics and genetic selection in purebred dogs. Reproduction In Domestic Animals 38: 73–6

Osborne CA, Lulich JP, Polzin DJ, Allen TA, Kruger JM, Bartges JW, Koehler LA, Ulrich LK, Bird KA and Swanson LL (1999) Medical Dissolution and Prevention of Canine Struvite Urolithiasis. Veterinary Clinics of North America: Small Animal Practice 29: 73–111

Snyder DM, Steffey MA, Mehler SJ, Drobatz KJ and Aronson LR (2005) Diagnosis and surgical management of ureteral calculi in dogs: 16 cases (1990-2003). New Zealand Veterinary Journal 53: 19–25

Stevenson AE and Markwell PJ (2005) Comparison of urine composition of healthy Labrador Retrievers and Miniature Schnauzers. American Journal of Veterinary Research 62: 1782–1786

Stevenson AE, Blackburn JM, Markwell PJ and Robertson WG (2004) Nutrient intake and urine composition in calcium oxalate stone-forming dogs: comparison with healthy dogs and impact of dietary modification. Veterinary Therapeutics: Research In Applied Veterinary Medicine 5: 218–31

© UFAW 2016


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