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13 minutes reading time (2536 words)

Cosmo's Urinary Stones - Part 2

Cosmo's Urinary Stones - Part 2
Cosmo was first diagnosed with calcium oxalate stones in August 2014. These were subsequently removed by surgery in November 2014 and he has been on a special diet since the surgery. The diet consisted of a combination of Royal Canin Urinary SO (moderate calorie) and a low oxalate homemade diet. Then in April 2016 Cosmo's stones returned and were again removed by surgery in August, 2016. So his special diet did little, if anything, to prevent the stones from reoccurring. That ineffective diet will be discussed below, but it was basically a low oxalate diet with supplemental water to further dilute his urine. This recurrence is typical for oxalate stone-forming dogs. Stones will often return within a couple of years.

Miniature schnauzers are one of several breeds that have a tendency to form oxalate stones. This may be due to some physiological abnormality, but little is known about the underlying cause of stone formation. The problem is most significant in male dogs since the urethra is relatively narrow and can become blocked with oxalate crystals, causing a life-threatening situation. Unlike some other types of urinary crystals, calcium oxalate cannot be dissolved. So it is best to prevent them by ameliorating the factors that appear to lead to stone formation by diluting the urine, reducing the levels of calcium and oxalate in the urine, and by increasing the pH of the urine. It is hoped that these goals can be accomplished through diet, but there is little evidence to support this approach. However, the alternative is to do nothing and risk yet another re-occurrence of stones and subsequent surgery. So a special diet seems worth a try.

One of the keystones of any diet for stone-forming dogs is increased fluid intake since the more water ingested the more dilute the urine will be as to calcium and oxalate. This is why canned food is usually recommended for stone-forming dogs since it is usually 70-80% water. Cosmo's ineffective diet contained about 72% water overall which provided about 12 oz (~375g) of water from his meals alone. Plus, he does drink some water between meals. I would guess his total water intake is about 13 oz per day. To put this in perspective, I would have to drink almost 3 liters of water per day to match this intake.

Dietary changes are not without potential problems. One needs to make sure no harm is being done when the diet is changed. The amounts of the various essential components of the diet are important (e.g., is the RDA of calcium being met; is too much vitamin A being provided), but also the interplay between some nutrients can be important (e.g., the balance between calcium and phosphorus), which adds to the complexity of the analysis. I should state that this sort of analysis would not be possible without software to quickly analyze diets for the various essential nutrients. Without it, one is basically "flying blind" with no firm idea what a change in a diet constituent will have on nutrients and calories. Fortunately, software such as this exists in the form of Pet Diet Designer.

Looking at Cosmo's ineffective diet, several things stand out. First, the protein level was about 300% of his RDA for protein. Some canine nutritionists believe that a low protein diet may be beneficial in preventing these stones. In humans, a high animal protein diet can cause a metabolic acidosis which causes acidic urine and even increased calcium excretion by the kidneys. Whether this is true in dogs remains to be determined.

Probably the most important change in his diet was to increase his water intake to keep his urine dilute. Most authorities recommended that his urine specific gravity be below 1.020. Without intervention, it is typically above 1.040. He rarely met this goal with his previous diet. So we increased his "soup" intake to 3 times per day (11am, 2pm and 5pm). Each soup course contains 30ml of low sodium bouillon plus 60ml of water and 15 grams of cooked rice. The soup along with this two meals (7:30am and 8pm) have increased his water intake per day to about 600ml.

Cosmo's urine is normally very acidic (~pH5) which may contribute to his problem with oxalate stones in his bladder. This acidic pH may inhibit certain macro-molecules that naturally inhibit stone formation. There are ways of increasing the pH of a dog's urine without reducing protein intake. Potassium citrate at 75mg/kg twice daily has been shown to increase urinary pH. The citrate is metabolized to bicarbonate which is then excreted in the urine to increase the pH. If citrate is excreted in dog urine to any extent, and there is some debate on this point, the citrate may also have the benefit of competing for calcium with oxalate, thus hopefully reducing the amount of calcium oxalate available for stone formation. Cosmo's ineffective diet did not include citrate.

Another potential problem with his ineffective diet was the level of calcium which was about 150% of his RDA. It is known that some miniature schnauzers absorb too much calcium from the gut which results in excessive urinary calcium. Cosmo's urinary calcium has not been determined, but his blood calcium has been within the normal range on two occasions (January 2015 and July 2016). Only about 4% of stone-forming dogs have hypercalcemia. It would be useful to know if his urinary calcium is also normal.

Sodium is another potential problem. His ineffective diet provided almost 630% of his RDA and most of this came from the Urinary SO. Some veterinarian nutritionists recommend high sodium levels to increase thirst and thus increase water intake which causes the production of more dilute urine. However, there have not been any studies to show that this effect is actually realized and there are some risks in giving too much salt.

Cosmo's ineffective diet did not contain sufficient quantities of vitamin D. It only contained about 60% of his RDA for this vitamin. In humans, vitamin D is formed in the skin when it is exposed to sunlight, but dogs do not form significant amounts due to their fur. Without sufficient vitamin D, which is important in the absorption of calcium, mechanisms might be activated to mobilize more calcium from the bones, again resulting in more calcium being secreted by the kidneys. This is obviously contrary to the hyper-absorption of calcium mentioned above. But regardless, his diet does need some additional vitamin D.

Finally, the diet he was on had way too much vitamin A, almost 1000% of the RDA for Cosmo. Even though we did not see any adverse effects from ingesting this amount of vitamin A, it makes sense to reduce it to a more normal level. A lot of the vitamin A came from the Urinary SO moderate calorie component of his diet.

Which brings up another point, why did we include the Urinary SO food in his ineffective diet? About 1/3 of the calories came from Urinary SO. This food provides a lot of vitamins and other nutrients that would not be present in sufficient quantities without its inclusion. Many leafy vegetables which are high in vitamins, especially the B vitamins, cannot be used in a low oxalate diet. So including the Urinary SO avoided the need to add vitamin and mineral supplements to his diet. Without Urinary SO there were about 20 nutrients that were not at 100% of his RDA or above. With the Urinary SO, there were only 5. This review using PDD was only possible because Royal Canin provides a typical analysis of their foods which provides detailed levels for amino acids, vitamins, and minerals. Other commercial providers of dog foods such as Hill's and Purina are less forthcoming with such data.

Obviously, his diet had to change if there was any hope of preventing a third occurrence of his stones. But what to do? I thought that looking at commercial diets for stone-forming dogs might be helpful. There are at least three on the market in the US as shown below. The protein values shown below are in terms of grams fed per day to Cosmo to yield about 550 Calories as are the fat data. RDAs are from Pet Diet Designer and are for Cosmo.

Commercial diet comparison

There seems to be little agreement on what constitutes an ideal diet. Low protein or moderate protein? Normal calcium or low calcium? High sodium or normal sodium? Include citrate or don't? Here are the values for Cosmo's ineffective diet: 

Cosmo's ineffective diet

Obviously, there is a big difference in the amount of protein included in the various commercial diets and there seems to be little agreement among veterinarian nutritionists as to whether a low-protein diet is useful in preventing stones. Yes, it makes sense to use less protein so that the urine might be less acidic, but as mentioned above, there is another way of achieving this therapeutical goal through the use of citrate in the diet. There are no data from feeding studies that I can find which justifies using low levels of protein in the diet. It is a good theory, but without studies to demonstrate that it is actually useful, I'm reluctant to go that route. Further, there is some epidemiological data that seems to indicate that high protein in the diet is actually preventative!

And another problem with an ultra-low protein diet is that the lost protein calories have to be made up with fats and carbohydrates. Miniature schnauzers have a tendency to develop pancreatitis and a high fat diet might be a problem. It was noted in a recent lab report that a sample of Cosmo's blood (non-fasting) required ultracentrifugation due to "gross lipemia." There is some evidence from studies in rats and humans that hyperlipemia may be a predisposing factor in the formation of oxalate stones. And finally, a high carbohydrate diet is not without its problems.

So given the fact that commercial dog foods provide little in the way of direction as to the amount of protein to use, and there is little data to support using low protein with its potential problems, I went with the middle ground and reduced the amount to about 250% of the RDA, from 316%. Hill's provides 116% of Cosmo's RDA; Urinary SO 258%, and Purina 286%.

I further reduced the calcium in the new diet to about 100% of his RDA from 150%. Cosmo's vet thinks that that the RDA set by the National Research Council is too high for calcium and prefers the minimum requirement (MR) used by pet food manufacturers. PDD will provide an analysis using either standard. Using this standard, the amount of calcium in Cosmo's new diet is about 180% of the MR.

The amount of sodium was reduced to about 330% of RDA (from 628%). And the amount of vitamin A was reduced to about 800% of Cosmo's RDA from about 1000%.

The final change was in adding calcium citrate to his diet. As mentioned above, citrate has been shown to increase the pH of urine, probably because it is metabolized to bicarbonate which is then excreted in the urine. Low pH urine is thought to reduce the effectiveness of natural inhibitors of calcium oxalate crystallization in the urine. Two of the three commercial foods for dogs that form oxalate stones contain potassium citrate, but the amounts are not specified. The usual recommended dose of potassium citrate would be about 1700mg per day for Cosmo. Since potassium citrate is about 62% citrate, the amount of citrate from this dose would be about 1000mg. I have used calcium citrate in his diet since he needed additional calcium, but there was no need for additional potassium. At 1.25g per day of calcium citrate (24% calcium 76% citrate), about 950mg of citrate is provided in his daily diet.

The following table summarizes the changes made in Cosmo's diet:

Changes made to Cosmo's diet

As mentioned above, more vitamin D needs to be in his diet. I purchased some pediatric vitamin D drops (400 units per drop) and add this to his food when make a batch (every 21 days). This brought his vitamin D intake up to about 250% of his RDA.

Below are two screen shots from Pet Diet Designer which show the analysis of the revised diet. One is in terms of the NRC Recommended Daily Allowances and the other in terms of Minimum Requirements. This is an analysis of Cosmo's daily diet including snacks, the "soup" he gets 3 times per day to increase his fluid intake and of course, some food from the table. Nutrients shown in yellow are those which do not meet the RDA for Cosmo. Vitamin K is produced by gut bacteria in the gut so dietary intake is thought not to be important. To see these screen shots in full size, click on the image and then right click on it and open a new window. The full sized image can then be seen by clicking on the new window.

Analysis of Cosmo's diet using NRC Recommended Daily Allowances
Analysis of Cosmo's diet using NRC Minimum Requirement

Here are two reports from Pet Diet Designer which provide more detail on the nutrient analysis. The Nutrient Report gives a good summary on the first page. The Recipe Analysis provides a good summary of the RDA analysis of the diet.

Click the "Pop out" button in the top right corner of the document container below to open a full page view of the report. Note that your browser must be able to view PDF files. If you do not see a document below either refresh this page or download a PDF browser plugin from www.adobe.com.

Nutrient Report
Recipe Analysis
 

One ingredient that is not shown in the diet analysis is the probiotic FortiFlora (Purina) that we give him once per week (1 packet). There is some evidence that certain microorganisms found in probiotics actually metabolize oxalate in the gut. Whether they are in FortiFlora has not been documented, but it is worth a try. The FortiFlora also guards against Clostridium overgrowth diarrhea which some dogs are prone to, including Cosmo.

I used the following reviews from the veterinarian literature to prepare this review of Cosmo's diet:

1. Jodi L. Westropp, DVM, PhD, DACVIM, UC Davis, School of Veterinary Medicine, Davis, CA, USA, Calcium Oxalate Stones in Cats & Dogs, WESTERN VETERINARY CONFERENCE 2008. This is a brief, but excellent review. I have yet to find it on-line. It was provided by a friend who had access to the conference proceedings. The review can be downloaded here.

2. Joe Bartges and Claudia Kirk, Nutritional Management of Lower Urinary Tract Disease, in Applied Veterinary Clinical Nutrition, First edition, 2012. I rented this book from Amazon.

3. Patricia Schenck, Diet and Urinary Tract Stones, in Home-Prepared Dog and Cat Diets, 2nd edition, 2012. This book was rented from Amazon.

4. Joe Bartges, DVM, PhD, DACVIM (SAIM), DACVN, The University of Tennessee, Knoxville, TN, USA,Rock 'n' Roll: Calcium Oxalate Uroliths – Medical & Minimally Invasive Management, WESTERN VETERINARY CONFERENCE 2013

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