I have a general article on kidney and bladder stones: http://www.2ndchance.info/calculi.htm , but most people write to me about the most frustrating type - calcium oxalate. I write these articles from memory so the prior article may include information I neglected to include here.
One of the most perplexing problems we face in veterinary medicine is the rising number of cases of calcium oxalate bladder and kidney stones in dogs and cats. Curiously, calcium oxalate stones have been increasing in number in humans in the US during this same time period. But they are only increasing in rich, pampered societies. Something that is usually not genetic must be happening. It either has to do with a change in activity (exercise) , environment or life-style or what we and our pets are eating. At the veterinary teaching hospital in Minnesota, cat records were reviews from 1981 to 2000. During that time, the incidence of oxalate stones increased 50-fold. In the United States, veterinary research receives much less federal support than does research the on human diseases. So I rely allot on research currently going on in humans.
There is a large amount of conflicting information on the internet regarding the best way to treat this problem. The reason for this is that no one really understands why some dogs and cats form these stones while others do not. Also, the period between new attacks of stone formation is highly variable. Not knowing the cause and not knowing if we have cured the pet make intelligent treatment very difficult. Most of the treatments given to dogs and cats with this problem rely on how calcium oxalate behaves in a test tube when various things are done to it. We try to avoid anything that might cause oxalate to come out of solution and form stones (calculi). But our bodies are so much more complicated than these simple laboratory experiments. I would be very dubious of anyone who offers a sure-fire cure to this problem - particularly if they are selling something. All though I do not believe that most cases have a genetic component, I do not thank that dogs or cats with a generational family history of this problem should be bred.
Since we do not know why some pets produce oxalate stones, no two veterinarians are going to offer you the same suggestions. There are veterinarians who specialize only in kidney and bladder stone formation - none have found the answer. The most notable individual in the United States is Dr. Carl Osborne at the University of Minnesota. You can not go wrong in following his recommendations.
One of my recommendations is that every owner of a pet with this problem have the means at hand to monitor it's urine specific gravity (the measure of the concentration or the urine) and urine pH (acidity) at home on a daily basis. That is the only way you will know if the treatment is working. This is not rocket science and the tool you need to detect over-concentrated urine is called a refractometer. Medical models are held in the hand and are only 6 inches long. They are economical and readily available to pet owners on Ebay. Be sure the instructions are included or plan on having a med-tech show you how. All pharmacies sell paper strips that tell you the acidity of urine. They work in any species. Twenty days after you begin your pet on a new diet and treatment plan, have the first urine of the morning analyzed with an RSS test (Relative Supersaturation Test). This test measures the likelihood that crystals will form in your pet's urine.
Many veterinarians prescribe potassium citrate to produce a less acid urine (higher pH). One brand is Urocit-K. It is not always effective.
Dogs with calcium oxalate stones are often older males. The most commonly affected breeds are Schnauzer, Lhasa apso, Yorkshire terrier, Bichon Frise, Shih Tzu and Miniature poodles. In cats, we see more of it in the Persian, Burmese and Himalayan breeds. So in some instances there is a genetic component.
Here is newer information that has come to light in human and lab animal research and which might be applied to our pets as well:
Anything that affects your pet's bones can increase calcium oxalate levels in the urine. Things such as too high or too low a vitamin D intake, or inactivity or arthritis. It is not clear if arthritis, such as hip dysplasia or spinal arthritis, directly elevate blood and urine calcium levels or if these pets are just not willing to exercise like they once did.
A peer-reviewed scientific article conducted in rats found that stress can cause the level of oxalate in the body to increase. This mechanism involves brain secretion firstly of vasopressin which acts directly to produce more concentrated urine and secondly adrenal gland secretion of cortisones which work through the parathyroid gland to raise blood calcium levels (not intestinal calcium levels which are actually helpful).
Another study in rats found that high diet supplementation with vitamin E markedly reduced the ability of calcium oxalate to crystallize in the kidneys. Perhaps this is applicable to other species. Vitamin E supplementation at recommended levels is quite safe.
Soy or soya-based dietary ingredients contain large amounts of oxalates. So do not feed pet foods that contain soy-based ingredients.
The amount of calcium in the urine is a major factor in calcium oxalate stone formation in pets and humans. There is some indications in humans that urine calcium increases in arthritis, increase the amount of calcium in the urine and causing oxalate crystals to form. This may be due to inactivity. Inactivity in children causes urine calcium to increase. So be sure your pet get plenty of exercise. In children, diuretics such as furosemide (Lasix) and vitamin D supplements also increases urine calcium. Diet in humans also influences the amount of calcium in the urine. The less phosphorus in the diet, the higher urine calcium concentration will be. The more salt, protein, glucose, sucrose, magnesium in the diet, the higher urine calcium will be. The greater water consumption is, the lower urine calcium will be. Because dehydrated egg whites have added sucrose (sugar), I am hesitant to use them as a food ingredient.
We used to believe that oxalate in the body came mostly from the things we eat. We now know that only about half comes from food. The rest is manufactured in the liver. What we now know is that only a small portion of the oxalate in food is absorbed from the intestine. And the higher the level of calcium in the diet, the less oxalate is absorbed. This is backward to the formulation of pet foods marketed to reduce urine oxalate. These foods are low in calcium on the mistaken theory that if we deprive the body of calcium, calcium oxalate crystals will not form.
The higher the amount of sugars in pet foods, the more oxalate is produced in the body. Isolated glucose does not have this effect. But table sugar (sucrose), grape sugar (fructose), milk sugar (lactose) all increase blood oxalate levels. Do not feed your pets milk products or diets that contain milk products because they contain lactose. Journal of Clinical Chem, Vol. 36 No. 10,1990 pg 1719-1720
A deficiency in vitamin B-6 (pyridoxine) also causes blood oxalate to increase. I would not give pets more than twice the recommended daily amount of B-6 unless I checked with a nutritionist. The National Research Council (NRC) has published recommended levels in pets.
The Mayo Clinics have developed a treatment protocol for people with oxalate stone problems. It includes prescription-level doses of vitamin B-6. Some also receive potassium citrate. Patients are encouraged to drink large amounts of water. They also encourage the consumption of calcium-rich foods. High calcium in the intestine links with oxalate and prevents it's absorption. Once the two bind, oxalate cannot be absorbed and it goes right through the intestine and is excreted in the feces. This means the oxalate never enters the bloodstream or the kidneys and never causes stones.
What Should I feed My Pet ?
This is the most common question pet owners ask me. I have a few recommendations based on the information I have learned. I suggest you not feed your dog or cat any commercial or homemade pet food that contains soybean derived products or soy. As mentioned the the Journal reference, soy products can be quite high in oxalates. This is particularly true when the soybeans are harvested early. I also suggest that commercial diets that you buy not be acidified for shelf life as an acid diet can create urine conditions conducive to oxalate stone formation.
In pet foods in general, low-cost meat byproducts are often substituted for more expensive human food-grade meat to save money. Pet grade meat by-products consist of organs and parts either not desired, or condemned, for human consumption. This can include bones, blood, intestines, lungs, ligaments, heads, feet, and feathers and whatever happens to be on the slaughterhouse floor at the time. When food-grade meat is used, it is often organ-derived (liver, kidney,lung etc) meat which is high in oxalate - particularly liver.
Every manufacturer of specialty pet food is going to tell you that his ingredients and diet formula is the best out there. All products in whichever diet you choose need to be human food grade. Manufacturers of specialty diets often make exaggerated claims for their products. Over-the-counter Dog Food Companies tent to go with the least expensive ingredients they can find. For instance, ground chicken feathers qualify as "poultry byproduct".
Many readers ask me what I think about Hills Prescription diet u/d. I have some reservations about it's formula. First, it is marketed as being low in calcium. But recent scientific data suggests that high calcium diets lower blood oxalate. It is also marketed as being low in phosphorus while recent research suggests that a low phosphorus diet increases the level of oxalate in the body. It's protein level is extremely low. I worry that a dog could exist on 8% protein for an extended time. I would prefer it at 12%. It contains the preservatives, BHT and BHA when vitamin E (tocopherol) could have been used. It contains soya-based ingredients. Dogs tend to dislike its taste and odor. Is largest ingredient is brewer's rice, a waste product of the alcohol industry. It does not state that it's ingredients are human food-grade quality. It's protein source is dried egg white powder. In producing this powder it is "stabilized" That is,, the glucose in the egg is removed and table sugar or corn syrup sugar is substituted for shelf life.
Hills Prescription diets k/d is often suggested to combat oxalate stones in cats. However, feline k/d's largest ingredient is also Brewer' Rice. It's next largest ingredient, chicken by-product produced from slaughterhouse waste. It does not state that it is human food-grade. It's next largest ingredient is dried egg whites which have added sucrose (sugar). It also contains soy products. It contains the preservative, ethoxyquin. It produces the acid pH urine that oxalate loves. It has reduced phosphorus.
Other brands that are frequently suggested by veterinarians are Waltham S/O Lower Urinary Tract Support; and Medi-Cal Reduced Protein Diet (Canadian). My choice would be Waltham's because the rational used in formulating their diet. Waltham Prescription Diets are manufactured by Royal Canin.
One has the most control over nutrition when you prepare your own pet's diet at home. I am not an enthusiast of raw diets because of the Salmonella and E. coli problem. If you make your own diet, you will need to measure urine pH, RSS and urine specific gravity after the pet has been on the new diet for 20 days.