Bladder Stones

"Bladder stones! Are you crating her too much? Is she getting enough to drink? It must be your water!"

These are often the reactions of Miniature Schnauzers breeders when faced with the news that a dog they've bred has been diagnosed with bladder stones. However, research indicates that these factors play little, if any, role in the formation of canine uroliths. To deal with this issue, the first step is to acquaint oneself with the processes behind the formation of the various types of stones. The differing mineral compositions can indicate vastly different disease processes. Likewise, they may have differing likelihoods that they are genetically based. Analysis of bladder stones and accurate record keeping may prove invaluable should future research unravel the genetics of these problems.

Although there are many types of stones known to affect dogs, Miniature Schnauzers suffer most commonly from either Struvite and/or Calcium Oxalate uroliths.

Struvite stones (Magnesium ammonium phosphate( are the most common type. Experimental and clinical studies have provided convincing evidence that the vast majority of Struvite stones occur following infection of the urinary tract with urease producing bacteria (especially staphylococci.) This infection results in the urine becoming more alkaline. Mineral crystals are less soluble in the alkaline environment and tend to clump together, forming stones. Studies at the University of Minnesota revealed that Struvite stones can form within 2 to 8 weeks following an infection. Some have been detected in puppies as young as 5 weeks.

As the stones form, they can lead to irritation of the urinary tract, making bacterial infection more difficult to treat. A vicious cycle begins. Untreated, bladder stones can lead to blockage of the urethra (particularly in male dogs) serious illness and death. This is a medical emergency. Any Miniature Schnauzer whom you suspect has a blockage (eg. straining to urinate) needs immediate medical attention!

Treatment of Struvite stones involves antibiotic and dietary management, urine acidifiers and/or surgery. Eradication or control of urinary tract infection is the most important factor in preventing recurrence. Researchers have evaluated Miniature Schnauzers with as many as 7 recurrences following surgery.

In a healthy dog the urinary tract has natural defence mechanisms to resist such infections. While these defences may be altered as a result of trauma, there is strong evidence that some Miniature Schnauzers have inherited abnormal defence mechanisms, allowing bacterial colonization to occur. This is especially suspicious in dogs with a chronic history of urinary tract infections.

Between July 1981 and December 1984, researchers at the University of California School of Veterinary Medicine (Davis) analysed 813 canine uroliths. Of 617 containing Struvite, 72 were from Miniature Schnauzers - nearly double the incidence of the next purebred breed. Average age of diagnosis was 5 years. Females were most commonly affected.

Mini Schnauzers also led all purebreds with the diagnosis of calcium oxalate stones. In this group the average age was 8 years and males predominated.

Calcium Oxalates are well researched in humans, but little is known about their formation in dogs. Also, they tend to form in the kidneys in humans and bladder in canines, so it may be risky to draw too many conclusions about calcium oxalate stone disease processes from human studies. Nonetheless, in humans they were due to metabolic causes, gastrointestinal hyper absorption of calcium (including abnormal vitamin D metabolism) and renal calcium leak. Calcium oxalate stones also seem to be on the increase in North America - there may be dietary factors involved.

Treatment of this type of stone lies with surgery - they cannot he dissolved with diet. However, dietary management may help in preventing recurrences.

Worthy of mention are a third form of urolith containing uric acid. The unique metabolism of Dalmatians placed them at the head of breeds affected, but Mini Schnauzers were second among purebreds. This type of stone is sometimes the result. of a Porto vascular shunt or liver disease. As MS have a relatively significant incidence of inherited hepatic shunts, the appearance of these stones in the Davis samples could be related.

Many stones will show varying combinations of minerals when analysed. This is sometimes indicative of different stages of disease processes that might, for example, have begun with a metabolic oxalate stone leading to trauma and infection of the urinary tract and the formation of Struvite layers.

Breeders who encounter any type of bladder stone would be well advised to investigate thoroughly the mineral composition (your vet can arrange this), recording the age of dog and any significant health issues. Careful record keeping may help provide clues to the likelihood that they are inherited.

If stone problems are occurring in related dogs, in otherwise young and healthy animals, or if there is a history of unexplained, chronic urinary tract infections, a genetic factor should be considered. Statistical evidence, as well as plain common sense, would suggest that there are inherited factors at work in the formation of bladder stones in the majority of Miniature Schnauzers affected.

Catherine McMillan
(Special thanks to Dr. Stan Rubin DVM, University of Saskatchewan Vet Teaching Hospital, for his assistance in providing background research material for this column).

©Copyright 1997, Catherine McMillan

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