As mentioned previously, Cosmo has had a recurrence of his calcium oxalate bladder stones. He has had two bladder surgeries to remove them since November 2014, and now another surgery seems inevitable. His latest crop of stones was found with an X-ray by our vet in late July, but we decided to put off the surgery until they create a problem (e.g., UTIs and/or blood in his urine). I think it is likely that he will continue to have recurring stones, so putting off the surgery as long as possible seems appropriate… he will form them again. I test his urine about every two weeks for a UTI, blood, glucose, pH, and specific gravity using test strips and a refractometer. We considered using a less invasive method of removing the stones (e.g., lithotripsy), but very few vets perform this procedure.
Another problem has come to light. Cosmo’s serum triglycerides are over 1000 mg/dl (normal range 29-291). His cholesterol is in the normal range. Hyperlipidemia is a fairly common problem in Miniature Schnauzers. The typical dietary treatment is to use a low-fat diet. So this condition makes his dietary requirements even more complicated… moderate protein (for stones), low fat (for hyperlipidemia), low calcium (for stones), and low oxalate (for stones).Â
So far, our attempts to prevent oxalate stones through a special diet have been unsuccessful (see previous blogs). After discovering the third crop of stones, the vet wanted us to feed him a commercial food that is designed to prevent this condition (Royal Canin, Urinary SO, canned, moderate calorie). I can’t find much evidence to justify this formulation, but since our homemade approach didn’t work, we decided to try Urinary SO. There was no chance that the stones would dissolve with this food, but it might inhibit more stones from forming. Cosmo seemed to like it for about a month and then decided he didn’t. Period… no discussion, so to speak. Cosmo has always been an enthusiastic eater, and at times he would stare at his bowl and walk off. He was not happy. So we switched him back to his previous diet, a combination of a homemade recipe and the Urinary SO (about 2/3 of the calories from the homemade). The diet is balanced and complete according to Pet Diet Designer (https://www.petdietdesigner.com) software. He then licked the bowl clean after each meal and continues to do so. I think I saw him smile when we switched him back to his homemade food.
But what to do about the stones? Perhaps something was sub-optimal about the homemade recipe. I needed expert advice, so I contacted a veterinary nutritionist (DVM, board-certified in nutrition [DACVN] and internal medicine [DACVIM]) with experience in diets for oxalate stone-forming Miniature Schnauzers. She had even published on this topic. She agreed to work with me on the diet. I provided her with extensive clinical data on Cosmo and asked her to review what we were feeding him and suggest changes to improve the recipe. Below is a summary of what I learned from this collaboration.
1. Suggestions to improve his current diet: The current diet has several issues, but the main one is too much fat. One of my goals for the consultation with the nutritionist was to define better the optimal calorie composition of protein, fat, and carbohydrates. The current diet has 23% protein, 36% fat, and 41% carbs as a percentage of calories. Some think too much protein can contribute to stone formation, too much fat to hyperlipidemia/pancreatitis, and too much carbohydrate to making diabetes worse if it develops. According to the nutritionist, a diet for a dog with a tendency to form oxalate bladder stones should contain about 25-30% protein, about 20% fat, and the rest carbohydrate (45-55%). Some believe a modest-protein diet results in less acidic urine and is therefore less likely to form oxalate crystals. Vets debate this approach to dietary control of oxalate stones. Little evidence shows that severely restricting dietary protein prevents oxalate stones, but keeping protein to about 25-30% of calories seems reasonable and is unlikely to cause other problems. If you use a commercial dog food, these percentages can easily be calculated from dry matter (DM) data on dog food labels using the following calories per gram: protein 4 calories/gram; fat 9 calories/gram; and carbohydrate 4 calories per gram.
Interestingly, Balance It (https://secure.balanceit.com/), a company that specializes in additives for homemade diets for dogs (and cats), suggests similar amounts of protein, fat, and carbohydrate (25%:25%:50%) in diets for dogs that form oxalate stones.
It was challenging to significantly reduce fat and increase protein and carbohydrates in Cosmo’s diet. For example, the Urinary SO canned food used in his diet contains 23% protein, 47% fat, and 30% carbohydrates. Also, the oxalate-free dried banana chips we use for treats (Cosmo loves them) are full of fat (macronutrient composition: 22%, 31%, 45%) because they are processed with coconut oil. The big problem is that fat has 9 calories per gram, while protein and carbs have only 4. So any fat reduction must be countered with fairly large increases in protein and carbohydrates to maintain the same number of calories—more on optimizing the diet below.
The amount of calcium in the diet is another variable to be considered. Calcium absorption from the gut is a highly controlled and complex process (both active and passive). Too much or not enough calcium in the diet can cause problems. The current diet contains about 1.15 g/1000 calories, which may be too low. The nutritionist suggested increasing calcium to about 1.7g/1000cal. Balance It suggests similar levels of calcium (about 1.85g/1000cal).
2. Clarification of nutrient standards: Nutritional standards (i.e., the amount of essential nutrients a dog must ingest to remain healthy) can be confusing, and it does not help that there are three recognized nutritional standards for essential canine nutrients: NRC, AAFCO, and the FEDIAF. I use Pet Diet Designer (PDD) software to analyze diets and determine the nutrient amounts in terms of Recommended Allowances (RA) as defined by the National Research Council (NRC). Some consider their 2006 standards the “gold standard” for these requirements, and they are based on scientific studies of nutritional needs as well as other factors such as the bioavailability of nutrients in foodstuffs. So, we know Cosmo’s weight (26.5 lbs), his age (9 years), and his activity level (modest), and from this, the PDD software can estimate his caloric need (about 580 calories per day). Likewise, it can estimate the amounts of 40 essential nutrients he needs each day based on NRC recommended allowances (i.e., the amounts Cosmo needs to ingest to avoid nutritional deficiencies). It can also evaluate a diet and determine if the RAs are exceeded and, if so, by how much.
The problem is that most veterinary professionals, including the nutritionist I have been working with, don’t typically think in terms of NRC-recommended allowances. They use a different set of standards for 38 essential nutrients from the AAFCO (American Association of Feed Control Officers). These are often very close to or identical to the NRC standards (15 of 38 are identical), but some differ significantly, including those for protein and calcium. AAFCO-recommended allowances are sometimes much higher. One reason they differ is that this organization sets standards for pet food, and the components of these foods are often not human-food quality. So, AAFCO takes the NRC standards and incorporates a “fudge” factor into the recommended amounts of some nutrients that accounts for bioavailability and other factors. Notably, not all AAFCO standards that differ from the NRC standards are higher. Many of the vitamin allowances are lower.
There is a third standard (FEDIAF) which defines the European nutrient standards for dog and cat foods. In many cases, these standards are even higher than the AAFCO standards. A summary of the standards from these three organizations is provided at the end of this blog. It is easy to get lost in the units of these standards when comparing them, but I’ve found that using concentrations such as the quantity of a nutrient per 1000cal makes it easy to compare the different standards.
One of the clearest statements I have seen regarding the relationship between these standards came from Rene de Montbrun, the creator of Pet Diet Designer (https://www.petdietdesigner.com). “AAFCO and FEDIAF are commercial standards that were created from the NRC standards to reflect better the decreased nutrient availability of ingredients commonly used in pet foods. There is a built-in “fudge” factor to ensure pets get the required nutrients. The NRC standards were designed for more purified feeds, where nutrient availability is higher than in ingredients used in pet foods. So whole food ingredients used by humans are better suited to the NRC standard.”
Balance It (https://secure.balanceit.com/) has a web-based software that can be used to evaluate homemade diets, and it uses the AAFCO standards. Both programs (PDD and Balance It) yield the same quantity for a given nutrient when evaluating a given recipe, but where they differ is in the recommended amount to maintain optimal nutritional health. For example, one PDD report listed the actual amount of protein in a particular diet as 42g/560cal or 75 g/1000cal. The Balance It report for that recipe lists protein as 77g/1000cal, which is close to the number given by the PDD. However, the Balance It report lists the protein requirement as 45g/1000cal, while PDD lists 25g/1000cal as the RA.
The Balance It software available to pet owners (i.e., non-professionals) lets you formulate diets for healthy dogs or cats. The food choices you can add to a diet are fairly limited compared with what you can use with PDD. You can use Balance It software for dogs/cats with a disease, but only with a veterinarian’s permission. Balance It facilitates obtaining that approval. See their website for further information. Balance It’s head, Sean Delaney, DVM, MS, DACVN, was associated with the vet school at UC Davis and was very willing to answer questions about their products and software.
Dogs’ nutrient requirements vary with age, activity level, temperament, life stage, health status, and diet quality. Too many variables make these standards an imprecise guide to an individual dog’s nutritional needs. In other words, these standards, including those from the NRC, should be treated as guidelines for a specific dog’s requirements, not as a precise statement of actual nutritional need.
Even the NRC RA standards vary depending on how the standard is defined. It can be defined in terms of the quantity of a given nutrient per kg of metabolic weight or in terms of a concentration of the nutrient, for example, per 1000 cal of metabolizable energy (ME). If I calculate the RA for protein using Cosmo’s metabolic weight, I get 21g, but if I calculate it based on the calories he needs to consume each day (580 cal), I get 14 g. This is a 50% difference! Then add the variation that can result from how daily calorie needs are calculated, with factors ranging from 90 to 130 times the metabolic weight. But the bottom line is that the NRC standards are certainly better than nothing. They guide those formulating canine diets and, if followed, prevent deficiencies. Pet Diet Designer uses the concentration standards (quantity per 1000cal of diet), but I have seen a noted canine nutritionist use the amount per kg of metabolic weight method. The latter method tends to overestimate the RA, but in most cases, this is not a problem. With Cosmo, however, where I want to define a moderately low-protein, low-fat diet, a good RA estimate is important.
One of the best reviews I have found on these standards is:
3. Improving the diet: This is Cosmo’s current daily diet (567 calories per day, including snacks and “soup”). The macronutrient composition is: 23% protein, 36% fat, and 41% carbs. We normally prepare a 21-day batch, place it in Ziploc bags (about 400g each), and freeze them until needed:
Main meals, ½ in the morning, ½ in the evening: |
| 40 g      Turkey, all classes, light meat, cooked, roasted |
| 15 g      Beef, ground, 90% lean meat / 10% fat, patty, cooked, pan-broiled |
| 8 g        Beef, variety meats and by-products, liver, cooked, pan-fried |
| 5.6 g     Fish, tuna, light, canned in water, without salt, drained solids |
| 12 g      Egg, whole, cooked, hard-boiled |
| 43 g      Rice, white, medium-grain, cooked |
| 22 g      Broccoli, blanched and frozen, chopped, without salt |
| 21 g      Cauliflower, blanched and frozen, without salt |
| 22 g      Peas, green, cooked, frozen, without salt |
| 2.5 g     Oil, canola |
| 2.3 g     Oil, coconut |
| 0.5 g     Omega-3 Fish Oil |
| 0.2 caps Nature’s Sunshine Kelp Capsules |
| 1.25 g   Bone meal |
| 0.01 g   Vitamin D drops, 400IU per drop |
| 120 g    Royal Canin Urinary SO moderate calorie |
“Soup” to increase water intake: |
| 240 g    Water, bottled, generic |
| 45 g      Rice, white, medium-grain, cooked |
| 90g       Soup, low-sodium beef broth, bouillon, consommé, with an equal volume of water |
Low-oxalate treats: |
| 15 g      Snacks, banana chips |
| 10 g      Snacks: pita chips, salted |
This diet was originally derived from the so-called Fuzzer diet (see previous posts). It may seem like an overly complicated diet, but when it is prepared in 21-day batches, it is easily compounded. A good-quality scale with +/- 1 gram accuracy is essential. Using PDD lets you use relatively complex recipes because it’s easy to evaluate a diet to ensure it is balanced and complete.
Note that the Royal Canin Urinary SO moderate calorie (canned) contributes about 1/3 of the calories and is used to provide several nutrients that would be sub-optimal without it (i.e., linoleic acid, phosphorus, potassium, magnesium, iron, zinc, selenium, iodine, vitamin E, vitamins B2 and B5). So, adding the SO was an easy way to increase these nutrients. However, it adds a lot of fat to the diet, and it is expensive. The total daily cost of this diet is approximately $2.62. I want to find a diet that does not require SO.
The “soup” is probably the most effective part of this diet for preventing stones. It dilutes Cosmo’s urine, which helps prevent calcium oxalate crystallization. With this amount of liquid in his diet (about 600ml per day total), his urine specific gravity is normally below 1.020. Without the extra fluid, the specific gravity would be about 1.040 or higher.
Besides the Urinary SO, the nutritionist pointed out the following ingredients as being possibly problematic:
- Coconut oil… adds fat; value?
- Banana chip snacks… too much fat
- Tuna… value? Mercury content?
- Kelp capsules… enough iodine?
- Bone meal… Heavy metals? Phosphate content?
- Turkey… change to ground turkey in the PDD recipe from the food item selected (turkey light meat). Ground turkey is what we use, and it has more fat than the “light meat” we used in the PDD recipe.
Another advantage of using Pet Diet Designer (https://www.petdietdesigner.com) software is that it lets you try different ingredients and quickly see the impact on calories, percentages of protein, fat, and carbohydrate calories, as well as all the essential nutrients a dog needs. As mentioned above, it also allows a somewhat complex diet since relatively few hand calculations are needed to evaluate a diet.
The following is Cosmo’s new diet. Note that this section has been revised. I had previously tried a new diet with a fair amount of beef jerky (homemade) and eggs as protein sources, but the diet did not seem to agree with Cosmo. So I revised the diet again to eliminate the jerky and eggs.
The total calories are 574 per day, and the macronutrient composition is 24% protein, 25% fat, and 51% carbohydrates by calories.
Main meals, ½ in the morning, ½ in the evening: |
| 25 g    Chicken breast, oven-roasted, fat-free, sliced |
| 25 g    Beef, ground, 90% lean meat / 10% fat, patty, cooked, pan-broiled |
| 8 g      Beef, variety meats and by-products, liver, cooked, pan-fried |
| 95 g     Rice, white, medium-grain, cooked |
| 20g        Cauliflower, cooked, boiled, drained, without salt |
| 20 g       Broccoli, frozen, chopped, cooked, boiled, drained, without salt |
| 25 g      Peas, green, cooked, boiled, drained, without salt |
| 0.75 g   Oil, canola |
| 0.75 g   Omega-3 Fish Oil |
| 0.4Â Â Â Â Â Â Capsules Nature’s Sunshine Kelp Capsules |
| 1.75 g    Bone meal |
| 0.01 g    Vitamin D drops |
| 0.5cap   Capsule potassium magnesium citrate caps |
| 0.250 g   Choline bitartrate |
| 120g    Royal Canin Urinary SO moderate calorie canned food |
“Soup” to increase water intake: |
| 90 g      Soup, beef broth, bouillon, consommé, prepared with an equal volume of water, no sodium |
| 45 g      Rice, white, medium-grain, cooked |
| 180 g    Water, bottled, generic |
Low-oxalate treats: |
| 10 g    Banana chips (unsweetened) |
| 10 g      Snacks: pita chips, salted |
| 5 g     Kellogg’s Corn Flakes |
Changes:
- I replaced the ground turkey with roasted chicken breast because it has a better protein-to-fat ratio (63% protein to 37% fat for chicken vs. 39% to 61% for ground turkey).
- I increased the rice to add more carbohydrate calories.
- I eliminated the coconut oil and decreased the canola to 0.75 grams… a good source of linoleic acid.
- The kelp capsules, the main source of iodine, were doubled.
- Bone meal… I use human-grade bone meal, so the heavy-metal levels are hopefully safe. One thing I like about bone meal is that it also contains phosphate. So I can increase calcium with little need to add more phosphate from another source to balance the two. I added enough bone meal to bring calcium to 135% of Cosmo’s RA and to bring the calcium-to-phosphate ratio into the PDD green range. I have used calcium citrate in the past as a calcium source since it also alkalizes the urine, which some think helps prevent calcium oxalate crystals from forming. However, I gave this to Cosmo for about a year, and it had no impact on his stone formation… in fact, they reformed faster than ever!
- Tuna… We always use light, rather than white tuna. Light is supposed to have 1/3 the level of mercury as white, which has 0.350 micrograms per gram (0.32 ppm). So his tuna has about 0.12 micrograms per gram. Since he ingests 11 grams per day, that is 1.3 micrograms of mercury per day. The EPA safe dose is 0.1 microgram per KG for humans. I assume it is similar for dogs. Since Cosmo weighs about 11.8 kg, he should be able to ingest 1.2 micrograms per day. Close enough. Other fish (e.g., salmon) can be used, but they have a higher fat content than tuna.
- Magnesium/potassium supplement… I use a Thorne Research product that provides 99mg of potassium and 70mg of magnesium per capsule.
- Choline bitartrate… Without eggs, his diet needed choline, so I take a supplement. I bought bulk bitartrate powder.
The nutritionist set the following nutrient goals for the recipe. The levels in the recipe are shown to the right.
Still some work to do. The PDD balance screen for this recipe is shown below. The only deficiency is vitamin K (12% RA), but the gut flora also provides this vitamin. So, is this diet better at preventing oxalate stones? It is hard to say it is better since the changes made have not been shown to inhibit stone formation. But I do think this diet is healthier. And I’m pretty sure Cosmo likes it. Future changes will increase the protein without significantly increasing the fat.Â
The following is a list of NRC, AAFCO, and FEDIAF standardsÂ
