About Oxalate Bladder And Kidney Stones In Your Dog
And How To Manage Them
(Cystic and renal calculi)
Ron Hines DVM PhD
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In this article, I use the words stones and calculi interchangeably - In Latin, “calculus” is a pebble and more than one are “calculi”
What Is Oxalate And Why Has It Formed Urinary Stones In My Dog ?
The chemistry of oxalates make them one of the most frustrating health problem that veterinarians and pet-owners deal with.
Oxalic acid is an organic acid produced in animals and plants when, sugars and other carbohydrates and carbon sources are metabolized. Oxalic acid does not circulate free in the body; it links to sodium or potassium in a soluble oxalate-salt form. But when oxalic acid finds itself in the presence of calcium, it has the ability to links to it too, forming a particular insoluble salt crystal - calcium oxalate. Your body and your pet’s body obtain oxalates in two ways, some of it is absorb from your diet and some of it you manufacture in your own body (primarily in the liver). In humans, about 20-50% is thought to come from diet and the rest to be manufactured “in house”, in dogs that percentage is unknown. Oxalates do not appear to have any necessary function in the body; they are just a metabolic end-product destined to leave the body through urine – much like urea.
A distinctive property of oxalic acid that makes it so dangerous is that once it has linked with calcium, it is practically insoluble (will not dissolve) at the acidities normally found within the body. That one unusual characteristic of calcium oxalate (that nothing will dissolve it) is what makes it such an exasperating problem in veterinary and human medicine.
A small amount of calcium oxalate is present in all urine. It is only when it is present in abnormally high amounts or when the total composition of the urine (crystallization kinetics) favor the layered growth of these crystals into sizable stones that they become a medical problem. These kinetics are though to be a complicated variety of urine factors that favor crystal growth or inhibit crystal growth (eg nephrocalcin). They are not well understood in pets or humans. (ref) We do know that the urine of dogs that form calcium oxalate stones tends to be highly acidic. (When a liquid is acidic, its pH is under 7)
When two or more dogs live in the same household and eat the same traditional canine diet, it is unlikely that more than one will develop an oxalate stone problem. Veterinarians and human urologists have pondered over why this is. They have written countless scientific articles on the subject but have never been able to tell you more than the cause is probably a combination of many individual things (multifactorial) things occurring in the affected pet’s or human’s body. Their advice continues to be “make as many changes in your pets nutrition and lifestyle that might (theoretically) slow oxalate crystal formation. Despite following that advice, some dogs will go on to reform oxalate urinary tract stones and some will not. And some pets that made no changes in their lifestyle whatsoever will never have a relapse of the problem again. Anyone who tells you more than that is not basing the statements on what we know in 2011.
any disease, there are probably genetic traits that make one dog more
susceptible to oxalate stones than another. Certain breeds are more susceptible
(bichon, schnauzers, etc.) but genetics
cannot account for the greatly increased number of oxalate-affected pets
veterinarians have seen in all dogs since 1981. Only lifestyle or nutritional
factors could account for that.
The signs will vary depending on whether the stones have formed in the dog’s kidneys, bladder or both. They will also be severe if a stone has moved from your pet’s kidney and lodged in one of its ureters or moved from its bladder and lodged in its urethra.
The most common sign owners notice is difficulty urinating. Dogs take longer to urinate, attempt to urinate more frequently. The amount of urine they pass with each voiding is often less and they will maintain a squatting or leg-cocked position longer after they no longer have urine to void. Some spend excess time licking their genital area subsequent to urination.
often notice that the final drops of urine are pink rather than its normal
The next most common way these stones are discovered is when the dog is x-rayed – either for vague signs of abdominal discomfort, colic, flank pain, a suspected urinary tract infection or seen on the x-rays when radiographed for some entirely different problem.
When oxalate stones are present in the pet’s kidneys for long periods without signs or unnoticed, the pet may come to the veterinarian already in uremia, due to the damage the stones have already caused to its kidneys.
None of these symptoms are specific to oxalate kidney or bladder stones - other types of urinary tract stones and abnormalities and infections of the kidneys, bladder or tubes that link them (ureters and urethra) can cause identical signs. Dogs, particularly male ones, with repeat urinary tract infections should be scrutinized particularly closely for the presence of urinary tract stones.
You can read an article on symptoms and diagnosis of urinary tract calculi in more detail here.
Since 1981, the veterinary college at the University of Minnesota has been home to the University of Minnesota Urolith Center. Most urinary tract stones that develop in pets are analyzed and identified at this facility. They are submitted by veterinarians around the World. Since the service began, the number of stones that are found to be composed of oxalates has steadily increased. In 1981, approximately 5% of the stones were composed of oxalate. But by 1999, 35% were. Concurrently, the number of the common urinary tract stones that are composed of struvite (magnesium ammonium phosphate) has dropped. You can read more about those statistics here.
This is not only in the United States. In Canada, the number of calcium oxalate stones has risen similarly and the number of struvite submissions has fallen. As in the US, calcium oxalate stones are most common in male dogs and struvite still the most common in female dogs. You can read the Canadian statistics here. The situation in Northwestern Europe is similar .
The Canadian studies also noted that slightly more oxalate cases occurred in dogs in the winter and in toy breeds. The pet's of owners living in large urban centers developed more urinary tract stones that pets and owners living in the countryside.
Although female dogs are susceptible to oxalate stones, many more occur in male dogs. More cases occur in midlife (5-9 years), rather than in younger or very old dogs. More cases occur in smaller and toy breeds than in the larger dog breeds (other than keeshonds). In order of frequency in California, the breeds with the highest frequency of calcium oxalate stones are Bichon Frise , Miniature Schnauzer , Shih Tzu, Lhasa Apso, Pomeranian, Cairn Terrier, Yorkshire Terrier, Maltese and Keeshonds. Breeds with the lowest frequency of calcium oxalate stones are German Shorthair pointers, Great Danes, Rottweilers, Australian Cattle Dogs , Labrador Retrievers , German Shepherds , Border Collies and Bull Mastiffs. You can read the source of much of that information here. You can read the statistics in Canada here.
Don’t assume that all these statistics are due to genetics; the small dog breeds that show the greatest incidence of oxalate stones are also the most popular breeds today - so there are more of them from which to submit samples. Also, the lifestyle of small breeds of dogs tends to be quite different from the lifestyle of the larger breeds. For example, larger breeds tend to spend more time outside with greater opportunities to urinate frequently throughout the day.
Your Veterinarian’s Physical Examination
The history you give your veterinarian may already cause her/him to suspect that your pet’s problem involves its urinary system. Over their careers, veterinarians become very deft at probing and palpating the tummies of pets. They can feel many things through the walls of your pet’s abdomen that might not be apparent to you. Some dogs are much easier to palpate(feel) than others. Fat dogs, large dogs, anxious dogs and dogs that are tensing their abdomens due to pain (splinting) are harder to palpate. Your veterinarian might notice that your pet is tensing its abdomen due to pain and that the area of its kidneys might appear to be the most painful.
Your veterinarian will be able to palpate your pet’s bladder. When bladders are chronically inflamed by stones or infection, they become thicker than normal. If a large stone(s) is located in your pet’s bladder and the pet is relaxed enough, that stone should be palpable to your vet. When several stones are loose in the bladder, they often grind during palpation – similar to a handful of marbles.
When a small stone has blocked the urethra, leading from the bladder to the penis, in male dogs, the vet can sometimes palpate it through the rectum wall using a finger cot.
In smaller, leaner dogs, the kidneys can often be palpated as well. When those kidneys are abnormally large or small or lumpy or hard, or of unequal size, your vet knows that something is amiss.
At that point, your veterinarian is going to want to do two things, examine your pet’s urine and x-ray its urinary tract.
One or two x-ray views (survey x-rays) of your dogs abdomen usually detect oxalate urinary stones when they are present. Both of the common stone constituents, oxalate and struvite, have a density similar to bone, so these more-or-less round objects are relatively easy to detect. Other forms of urinary stones (urate, phosphate or cystine) can be much harder to see (less radiopaque).
Survey x-rays will not detect all oxalate stones. Very small ones can be missed when only a few are present or when a single stone has plugged the dog’s urethra or ureter. But survey x-rays detect stones in about 8 out of 10 dogs that have them. When calculi are small, stool in the colon can obscures them. So your vet may give your pet an enema prior to the x-rays.
If no stones are seen, but your vet still suspects them, the vet may use a more complicated, but more sensitive, technique to detect them. (double-contrast cystography)
Your Pet’s Urine Specimen Examined In The Lab
All veterinary hospitals have small reagent strips of paper that give a color indication of the things that are present in urine. They are the same strips physicians use. In most cases of urinary tract stones that I have dealt with, these strips will indicate the presence of blood in the pet’s urine. They may also be positive for the presence of nitrite – an indication of urinary tract infection. The strip also indicates the acidity (pH) of your pet’s urine. If the pH is less than 6.5, it may make your veterinarian suspicious that the stones are composed of oxalate. Some strips also give a crude measurement of urine concentration (specific gravity = SG). However, pH and specific gravity during a crisis is not a good indication of what your pet’s day-to-day urine characteristics are.
You veterinarian will centrifuge the urine specimen and examine the sediment that forms on the bottom of the tube. The presence of an abnormally high number of white blood cells confirms urinary tract infection or inflammation and small crystals of oxalate or other stone-forming elements may be seen as well. Bacteria play an important role in the formation of struvite stones, they do not appear to be an important factor in the formation of oxalate stones.
If your pet managed to pass a stone or if stones were removed from your pet in some other manner, they will most likely be sent on to the Minnesota Urolith Center to determine what they are made of. That is the only sure way to tell one type of urinary tract stone from another. It is important to do that because the treatment for each type of urinary tract stone is different. Occasionally the results will indicate that your pet has formed compound stones that contain elements of more than one common type. In that case, it will need treatments directed at both. You can read more about urinary stone analysis here.
Bacterial Culture Of Your Dog’s Urine
When any foreign object is present in your pet’s urinary system, it is common for bacteria to hide within it. Urinary tract stones are porous, and these pores give bacteria places to hide and avoid the body’s natural defenses to eliminate them. In some cases (struvite stones) it is often the urinary tract bacterial infections that gives rise to the stone. In the case of oxalates, it is usually the opposite.
the cause, all urinary tract infections need to be eliminated with antibiotics.
One can not know for sure which antibiotic is the best to use, unless
the urine is cultured and the bacteria’s sensitivity to antibiotics
is determined (= MIC).
For your veterinarian to obtain an accurate sample of your pet’s urine, it will need to be collected through a urinary catheter or a needle placed through the pets abdominal muscles (cystocentesis).
Yes, it can.
always need to be able to pass their urine. If the tubes leading from
each kidney to the bladder (ureters)
or the tube leading from the bladder to the penis or vagina (urethra)
are blocked (obstructed), your dog’s
condition will deteriorate rapidly. Dogs rely on urination to regulate
their body’s water and blood ion (electrolyte)
balance. The ability to urinate is also critical in maintaining the pet’s
proper blood acidity and in eliminating the waste products of metabolism.
The most common crisis situation is a male dog with a stone present in its bladder
that is just small enough to enter its ureter but not small enough to
pass through the narrow portion surrounded by its os
If this blockage lasts more than the greater part of a day, one of these blood ions, potassium, that is normally excreted through its urine can reach dangerously high levels. Abnormally high potassium levels (hyperkalemia) affects the ability of the heart to beat normally (cardiac arrhythmias). Obstructed dogs quickly become depressed and weak. They usually experience nausea and vomit. When partially or fully obstructed dogs are left untreated, the abnormally high pressure of urine behind the obstruction leads to rapid destruction of the pet’s kidneys.
dogs that have repeat episodes of this problem, a surgical procedure called
a perineal urethrostomy can be performed that vents the urine from your
pet’s bladder and urethra before it passes through the penile bone
where they usually lodge. (the os penis).
You can read how that procedure is performed here.
The unfortunate reality is that physicians and veterinarians have nothing that will dissolve calcium oxalate stones in you or your pet. Calcium oxalate will dissolve – but only in solutions too alkaline for the body to tolerate. (ref)
So most calcium oxalate stones need to be removed surgically.
dogs are very fortunate, a single small stone or cluster of stones can
be removed through a non-surgical technique called urohydropropulsion. In that technique,
the natural elasticity of the urethra under forceful urine flow is used
to allow small stones present in the dog’s bladder to make their
way out via the urethra – much like a water balloon jet increases
the diameter of the balloon’s neck when you squirt someone at a
party. Saline solutions are passed up a catheter and into the pet's bladder
to provide the liquid volume needed. The technique works best in dogs
weighing more than 18-20 pounds and when the estimated diameter of the
calculi is no greater than 5mm. Dogs need to be anesthetized and held
in a position so that gravity assists in increasing the force of the urine
stream. The technique is more successful in female dogs than males. It
is not without hazard because it is possible to rupture the bladder if
pathology has weakened its walls or if the procedure is performed too
forcefully. You can read about the procedure here.
When dogs are large enough to allow the passage of instruments up the urethra and into the bladder, it is sometimes possible to nibble away or crush bladder stones into fragments small enough to leave the pet naturally in its urine or net them up in a small basket-like apparatus and draw them out the urethra that way. You can see what one of these devices look like here. It is not a technique you will find performed by veterinarians in general practice; but it is performed by specialists at a number of university veterinary hospitals. Some of those Centers are listed in the next section on Lithotripsy. When a dog is cat-size and the diameter of the tract is too narrow, the bladder can be approached through a tiny skin incision (percutaneously).
The majority of dogs with calcium oxalate bladder stones must undergo surgery to remove them. It is the simplest, and most direct way to remove them and the techniques to do it are readily available at surgical centers throughout the USA and Europe. Luckily, the majority of calcium oxalate calculi form in the bladder (about 90%). Unless your pet has multiple health issues, the surgery to remove them there is rather straightforward and recovery is rapid.
But removal of these stones when they are present in your pet’s kidneys or ureters is much more difficult and, possibly, even unwise. The decision to do so or to let matters remain as they are is best left up to an experienced, board-certified veterinary surgeon experienced in those matters. There are only a few of them in the United States and they are located at the same veterinary centers where lithotripsy is performed. Because there are so few of them, and because their techniques, equipment and success rates vary, there will be cases when they will not all agree on the best decision. At a minimum, the insertion of stents should be considered if a stone threatens to block a ureter.
The smaller the dog, the more delicate kidney or ureteral surgery becomes but the decision is also based on the location within the pet’s kidneys and any evidence that the calculi are obstructing urine flow. Other factors that enter into the decision as to removal of kidney stones (those actually in the kidney) are the frequency of urinary tract infections, the shape, size and number of stones and the rate at which they are increasing in size and the number of times the problem has reoccurred after prior surgeries.
Larger calcium oxalate stones, found in the bladder, are often mixed with sandy grit of the same material. When this grit is present in your pet’s bladder, the lining of the bladder will be highly inflamed and thickened, so it is very difficult to find and remove every last grain of calcium oxalate. Any that remain after surgery serve as seeds for new calculi to develop. Veterinarians must be extremely careful to flush away every last grain of that material. But even then, up to 20% of the time they may miss some.
You can read about the decisions that went into the determination in a single case here.
Lithotripsy is a procedure whereby urinary tract stones are broken up (fragmented) into pieces small enough to pass out of the pet’s body, either naturally or with assistance. It avoids a large surgical incision and, in some cases, any surgery at all.
are two ways to do this. The common method in humans is also performed
by a few veterinarians in dogs and cats. It is called extracorporeal lithotripsy
and more widely practiced form of lithotripsy uses a laser to destroy
the stones. The most commonly used apparatus is a holmium YAG laser. In
this procedure, the conduit conveying the laser energy is inserted up
the pet’s urinary tract until it is in direct contact with the stone.
I know of less than ten veterinarians World-wide who are competent to perform this procedure. All are in the US and Canada. Although the Royal Veterinary College, London, expressed an interest in providing the procedure, they had not done so as of 2008.
Many of my links go to articles written by these specialists. Please do not pester them with questions. Your local veterinarian is the one who needs to make those contacts for you. If these specialists complain, I will have to remove their articles.
Extracorporeal lithotripsy is available at both the Animal Medical Center (AMC) in New York, Purdue University Veterinary School and the University of Tennessee .
Laser lithotripsy is available at AMC, The University of California Veterinary School in Davis, The University of Minnesota Veterinary School’s , Minnesota Urolith Center, the Veterinary School at Purdue University and the Cummings School of Veterinary Medicine at Tufts. It is also performed at the veterinary school in Montreal and in Guelph .
There may well be other veterinary centers performing lithotripsy that I am unaware of.
Both techniques have their advantages, disadvantages and possible complications when compared to surgery.
The cost of these procedures are currently $1,500 – $7,000.
The size of your pet, its sex and the location of the stones decide if these procedures can be used. When they can, and when the cost is not prohibitive to you, they are an option that might spare your pet from traditional surgery. The outcome of any procedure this complicated can never be fully predicted, so these specialists are either expert surgeons themselves or have one close at hand.
Should I Consider Those High-tech Procedures For My Dog ?
In most cases, a skillful veterinary surgeon can remove urinary tract
Oxalate bladder stones are painful to your pet. And small stones that block its urethra can be fatal. Your veterinarian may be successful in pushing small stones back into the pet’s urinary bladder to gain time. But oxalate bladder stones tend to have rough surfaces that irritate the bladder lining and lead to chronic urinary tract infections. When stones are composed of struvite, you probably have non-surgical options. But when they are composed of oxalate, you do not.
Some veterinary specialists do not always recommend surgery when calcium oxalate stones are located in your pet’s kidneys. They distinguish between those they consider “clinically active” and those they consider “clinically inactive”. In some of those cases you probably do have the option to “manage” the pet - periodically checking it for bacterial infections, discomfort or evidence that the stone(s) are obstructing urine flow. That is particularly true if you pet has multiple health issues or if the stones have returned after a prior surgery.
There is a reason these veterinarians may be reluctant to remove kidney stones. It is because the surgery or procedures necessary to remove them sometimes damages the kidneys themselves. Since so few veterinarians in the World possess those skills and highly specialized equipment, my advice to you is to have radiographs and medical records from your pet sent by your veterinarian to one of the urology centers I mentioned earlier.
If you do not make major changes in your pet’s lifestyle and nutrition, the likelihood of your pet reforming oxalate stones is quite high. Somewhere around half of the dogs that experience one incidence of calcium oxalate stones will go on to have another attack within three years. It will take considerably more than just feeding a commercial prescription diet purported to prevent oxalate stone formation to change those odds.
If your pet’s calculi were removed surgically, your initial visits will be to be sure the surgery went well and that the pet’s urinary tract allows for the free passage of urine. Your vet will also run tests to be sure the pet is free of infection. X-rays will have been taken when the surgery was completed to be sure all stones were removed. It the pet was treated with lithotripsy, it is not that uncommon for a second lithotripsy to be required to break up residual stone fragments or for other procedures to be used to assist you dog in purging itself from the granular debris.
From then on, the visits will be to access the success of the dietary and lifestyle changes you have made in your pet’s life. Although the veterinarian may check your pet’s blood for calcium level, acidity (TCO) or other problems that may have contributed to the problem, the most important periodic examination will be the characteristics of your pet’s urine. Unless the urine is to be cultured for bacteria, there is no need to catheterize the pet – a fresh clean-catch specimen is sufficient.
Your vet will want to do periodic x-rays to see if the stones have returned or if those that could not be removed have moved or grown in size.
Your veterinarian will want to analyze your pet’s urine periodically. (Some veterinarians recommend that as frequently as every two months, indefinitely) The vet will be particularly interested in your pet's urine pH, urine specific gravity or any indication of blood or infection. The vet will also look at the sediment present in the urine specimen for any signs of oxalate crystals.
The best urine to bring in for testing is the first urine of the day – before your dog has eaten. It should be free of contamination, refrigerated or chilled and brought to the animal hospital as rapidly as possible. A foam cup, taped to a broomstick helps in collection. You do not need much – a tablespoon full will do. You can also attempt to get your pet to pee on a layer of Saran Wrap and transfer what you can to a cup. Cover the sample with a piece of Saran Wrap held in place with a rubber band or ask your vet for a urine collection vial.
Owners who are not health professionals cannot identify crystals or bacteria microscopically. But they should learn to perform some of these simple tests themselves. Owners who perform these simple tests at home are more likely to test their pets frequently and so they are more likely to have better outcomes. You can read the instructions for one popular brand here. You can buy them online or at your local pharmacy. No prescription needed.
No veterinarian has a foolproof plan to guarantee that your dog will not produce oxalate stones again. That is because no veterinarian knows for certain why some dogs develop these stones and others do not. What veterinarians can do is use their general knowledge of oxalate chemistry and dog metabolism to accomplish things we think would be helpful in preventing a relapse in your pet:
water consumption = dilute urine. From what we know about calcium oxalate,
it is very unlikely to crystallize into discrete, urinary tract stones
when your pet’s urine is dilute – even if oxalates are present
at the time. A Waltham study found that breeds of dogs that generally
drink more form less oxalate stones than breeds that do not (miniature
schnauzers vs Labrador retrievers) – although one can
not say for sure that one influences the other. (ref)
Observations at the University of Minnesota were similar (Osborne,
C. The Rocket Science of Canine Urolithiasis Veterinary Clinics of North
America- Small Animal Practice 29(1) January 1999). There
are several ways that you can increase your dog’s water consumption.
They include feeding you dog only canned, frozen or home-cooked diets,
moderately increasing the amount of salt in your dog’s diet, and, in carefully
chosen cases, administering diuretic medications like hydrochlorothiazide.
There is a section on each of those options below. You will only know you are
succeeding by measuring the specific gravity of your pet’s urine on multiple occasions.
Because the most important things you can do to prevent urinary stones from reoccurring is to keep your pet well hydrated and it’s urine as dilute as possible, you need to take special care to monitor it. We measure the degree of dilution of urine by its Specific Gravity. The lower the specific gravity, the more dilute the urine sample is. Aim at keeping your pets urine specific gravity below 1.025. Because low specific gravity is so critical, it is safer to measure it with a specific device called a refractometer, rather than to rely on the readings obtained from Multistixs and similar urine dipstick strips.
I encourage all my clients with stone-forming pets to purchase a refractometer. Do not be intimidated by the gizmo’s name or weird construction – it will not bite and it is very easy to use. Once you get the hang of it, your readings will be as accurate as a PhD chemist. Just be sure the instrument has been calibrated to zero with distilled water and that you are reading the specific gravity scale (SP) , not the serum protein (SP) scale. You can read more about urine refractometers and urine specific gravity here.
Oxalate stones only form in urine that is acidic. We measure acidity by the pH of your dog’s urine. It is normal for dog urine to be acidic (pH less than 7) – dogs are basically carnivores, and all carnivore urine is acidic. Urine that is too basic (pH more than 7) brings its own set of problems. Most dogs that initially come to veterinarians with oxalate stone problems have urine pH of 6.5 or less. You need to make changes in your pet’s nutrition and lifestyle that keep its urine pH consistently higher than that. I suggest aiming at between 6.6 and 6.8, but these recommendation vary greatly between veterinarians. Urine pH is another test you can easily perform at home using urine dipsticks or color-indicator paper. The sample to check is the first fresh void of the morning. Urine pH varies during the day. After your pet has eaten breakfast, its urine pH will begin to rise from its nighttime levels. You may not be successful in keeping your pet's urine pH where you want it. When you can't, remember that as far as we know, dilute urine trumps less acidic urine. That is, it is more important to keep your pet's urine dilute than to raise its pH.
Dogs that are free to urinate when they wish appear to be less susceptible to oxalate bladder stones than dogs that must wait for their owners to return home from work. Fewer urinations and lower urine quantities were found to be associated with greater potential for oxalate stone formation (RSS index).
Lack of opportunities to pee throughout the day might also account for the fact that dogs in urban Toronto have a significantly greater incidence of oxalate bladder stones than those that live in the surrounding rural areas. The abstract is here. A pdf of the entire study was given earlier. (Wisener2010b.pdf)
The acidity (pH) of your dog’s urine fluctuates during the day. It is usually lowest during the night and then slowly rises after the pet’s morning meal (postprandial alkaline tide).
So having many chances to munch during the day should give your pet a urine pH profile that is less acidic and therefore, less conducive to oxalate stone formation. Give it its last meal shortly before you go to bed. Just be sure that the total amount you feed your pet does not increase. We do not want your dog to become overweight. You can read more about those pH fluctuations in relation to eating here. Frequent small feedings might also minimize the postprandial (after meals) increase in urinary calcium that is thought by some to occur. (ref)
Much of my advice on prevent oxalate urinary tract stones relies on research conducted at the Waltham Centre For Pet Nutrition, located in Waltham-on-the-Wolds, Leicestershire, UK. The Center conducts nutritional research on dogs and cats there and funds promising projects elsewhere.
In an attempt to predict oxalate stone formation before it occurs, Waltham pioneered the use of relative supersaturation (RSS) testing in pets. RSS testing predicts when conditions in your pet’s urine are conducive to stone formation and when they are not. That is critical information to know, because it allows you to decide if the changes you have made to your pet’s diet and lifestyle are working. If you plan to prepare your dogs meals at home, RSS and a standard urinalysis are a good way to see if you are on track. If you feed a commercial canned diet designed to prevent oxalate stones, RSS and urinalysis are a good way to decide which brand is working best for your dog. Although RSS makes sense theoretically, there are no scientific studies to prove it actually works in dogs or humans. You can read about RSS testing here.
Although this is a great test, there is one problem - no US labs that I know of offer it for pets. Quest Diagnostics offers the tests to people who have a calcium oxalate stone problem but their veterinary division does not. You can see what a typical report looks like here. Only physicians can submit samples - perhaps you will have better success in dealing with that than I.
It is always prudent to run standard blood chemistry panels from time to time. This is especially true when oxalate stones remain in your dog’s kidneys or when there was any prior elevation of blood BUN or creatinine levels.
There are a few dogs that develop oxalate stones because their blood calcium levels are abnormally high (hypercalcemia). Some of these dogs often have underlying hyperthyroid gland problems . Keeshonds are noted for this problem (ref) ; but it can occur for a number of reasons in any dog. (ref)
Periodic x-rays are important in detecting new calculi that may form and in judging the growth and position of calculi that have not been removed. When calculi are discovered early, it might be possible to removed them from the bladder through urohydropropulsion or extract them in a retrieval basket through the urethra or through a very small abdominal and bladder incision.
Veterinarians have traditionally dispensed potassium citrate solutions to dogs that have developed oxalate stones. The hope was that when the citrate passed out in the dog’s urine, it would tie up urine calcium making it unavailable for calcium oxalate formation. It was also hoped that the citrate would keep the urine less acidic.
Some studies make it unclear if this theory holds up. Certainly, to have a continuous effect, the potassium citrate would have to be given many times during the day. If not, it would probably be best to give the whole daily dose at bedtime because we suspect that night time conditions are most conducive to stone formation. That link was given early in this article Stevenson2000potassiumcitratepH.pdf
that keeping your dogs urine specific gravity under 1.025 was very important
in preventing reoccurrence of stones because all forms of urinary tract
stones are less likely to form in dilute urine. When you can not achieve
that with canned or fresh diets and water supplementation, some veterinarians
resort to medications that make your pet thirstier and urinate more. These
are the diuretics. The most commonly used non-thiazide diuretic, furosemide, is not used
because it is known to increase the calcium content of urine - something
we do not want. So some veterinarians give these pets thiazide
One of the simplest ways to increase your dog’s water intake is to increase the saltiness of its food. Based on what they had read about human medicine, there was a time that veterinarians thought that doing so would increase the calcium content of urine which might aggravate an oxalate stone problem. But that does not appear to be true in cats. The higher salt diet produced urine was more dilute an less likely to form calcium oxalate stones (based on a lower RSS). You can read about the study done in the US here and the one in the UK here. Despite those results, recommendations regarding optimal salt content in your pet remain confusing. (ref)
we hear everyday that we ought not eat salt. And certain people probably
should limit their salt intake. But the most recent study in dogs found
that a low sodium diet in otherwise healthy dog might cause more damage
than good (ref) and the most recent human study found the same thing in otherwise healthy people. (ref)
Have your pet’s blood pressure, heart and kidney function checked in 2 months and then occasionally if you increase its salt intake significantly. Don’t get carried away - if it tastes too salty for you, it’s too salty for your dog.
Special diets will not dissolve calcium oxalate stones that have already formed. But dogs that have had an episode of calcium oxalate bladder or kidney stones have special needs. They should not be fed dry dog chow again and they should not receive a diet that contains plant products that are high in oxalates.
If you prepare your dog’s diet yourself or feed it considerable foods you yourself eat, there are food ingredients you really should avoid feeding. You can read a list of those foods here.
You can purchase many diets from your veterinarian that were designed, theoretically, to reduce the likelihood of calcium oxalate urinary tract stones. Whether these diets actually work, is unknown. They are all formulated to provide as little dietary oxalate as possible, provide no more than the necessary amount of calcium and attempt to keep your pet’s urine pH and specific gravity in acceptable ranges. If you determine, through urinalysis, that they are doing that, they are fine. If not, they are not fine. These diets are a Godsend for dealing with struvite stones; they are not nearly as effective in managing oxalate stones. So do not let using them lull you into a false sense of security that the problem is solved. Remember that a relatively high percentage of dogs will reform calcium oxalate stones on or off these diets. So you still need to monitor your pet’s urine specific gravity and other parameters of its urinary tract health.
You can also make your pet’s diet at home. Most dogs that develop oxalate problems are small, so you do not have to prepare large quantities. The diet you prepare should be made from the same quality ingredients that you eat. That is the only way you will truly control what is going into your pet. It should be based primarily on meat, with the addition of moderate amounts of low-oxalate vegetables. It needs a source of supplemental vitamins as well as calcium. You can find suggestions in that same article mentioned above. Contrary to what is often written, there is no evidence that protein restriction is beneficial to dogs with calcium oxalate problems. You can read two recent US studies on that here and here.
Red meat, chicken and turkey are quite low in oxalate, organ meats, like liver, can be higher because much of the oxalate formed in the body is produced in the liver.
Remember, what you feed is not nearly as important as the effects it has on your dogs urine concentration (specific gravity) and pH. There is evidence that some “stone-forming” dogs absorb and process dietary ingredients differently than non-stone forming dogs. Focus on how diet and lifestyle are effecting your dog's urine, not just on what it is eating.
Do not feed your dog products that contain soy or yellow corn or ingredients that are derived from soy or corn. Soybean products have the potential to be very high in oxalates. (ref)
same goes for corn and corn-derived products (the amount
in feed corn = hard yellow corn appears to
be more than in white corn). Many pet foods , both dry and canned,
are chocked full of yellow corn products and corn gluten isolates to boost
the label’s protein content. Besides being potentially high in oxalates
, corn glutens have the potential to make your pet’s urine too acidic.
Raw diets are not a good idea for pets with oxalate urinary tract stones if they contain vegetable ingredients. Boiling, and discarding the water that was used, greatly reduces the amount of absorbable oxalate in vegetables and grains. (ref)
Do not attempt to increase your pet’s water intake by pouring water on dry dog food in hot weather or when the food will stand for more than an hour. Bacterial growth in the mixture can cause digestive upsets. The same goes for leaving canned food at room temperature for long periods.
If I Prepare My Cat's Diet At Home, Should I restrict It's Calcium Intake ?
That is probably not a good idea. Calcium Oxalate does require free urine calcium to form. So for a long time, both physicians and veterinarians thought that restricting dietary calcium would help prevent oxalate stones. That theory did not hold up. You can read a bit about that here.
One reason is probably that the lifestyles of owners and pets have also changed dramatically over the last 30 years. There is been a shift to smaller breeds, that appear to be more susceptible to the problem and more owners are working full time and unable to provide spaced intervals for their dogs to urinate and exercise during the day. We know that lack of exercise predisposes humans to calcium oxalate calculi. (ref) Perhaps it affects dogs similarly.
there is another reason. It is the pet food industry itself. The last
30 years have seen two important changes in that industry. Conglomeration
into a few megafirms that dominate the World pet food market , a worldwide
explosion of demand for prepared pet foods and intense competition for
limited animal protein resources (meat-based products)
Conglomeration means limited competition and increased focus on profitability. As in all industries , without competition from smaller start-up firms, the incentives to produce quality products decreases. Exploding demand for meat-based products has driven up the price of these ingredients. To maintain profit margins and satisfy investors, these companies have had to search out other sources of protein than meat. The price of plant-source proteins has remained more static over that period. That is why these firms funded an explosion of research attempting to prove that dogs would do just as well if a major source of the protein in their diets was cheaper plant protein (soy and corn gluten). God created dogs as carnivores – meat eaters. You only need to look at their teeth to know that. There were bound to be negative consequences of feeding them primarily plant-based , rather than meat-based diets. I believe that the dramatic increase in the rate of calcium oxalate urinary stones is likely one of them.
Pet Food Conglomerates are masters at serving up cheap food ingredients wrapped in fancy labels and snazzy TV add campaigns. Let’s look at the ingredients in a popular Nestlé’s (aka Purina) product, Chef Michael’s. It’s no better and no worse than the other mass-market dog foods you find at your retailer.
take Chef Michael's Filet Mignon Flavor Dry Dog Food for example: 32%
protein, 18% fat and about 42% carbohydrates. All dog owners know their pets
like meat protein – so that looks good. Besides, you’ve seen the
add on TV with the Chef cutting up that good-looking ribeye !
Hmm.... Beef is listed as the first ingredient – that sounds good. But beef is 65-75% water and the other ingredients are dry. So they are not comparing apples to apples. If you considered the beef more accurately – as to how much it contributed to the dry mix – it would be way down the list. But these companies know that pet owners like to see meat as the first ingredient and there is no USDA rule against this slight-of-hand. The soybean meal and soy flour are actually the primary ingredients that Chef Michael puts in his dog food – but you don’t see Chef Michael cutting up soybeans or corn. Soy is known to be very high in oxalate. (ref 1, ref 2) . The soybeans are added solely to make this a high protein product while still retaining a high profit margin. There is debate as to whether soy protein is inferior to meat protein. (ref 1, ref 2) But there is no debate in that soy products are very high in oxalate.
Brewers rice is a byproduct of human rice cultivation – not something in beer. It is made up of the culled, broken grains resulting from the rice milling process. (The fragments that pass through a #4 sieve but not a 2.5 sieve). It is added to keep the meat to the front of the ingredient list and the corn products lower down. It also adds starch necessary to form the extruded pellet.
Corn gluten meal is a byproduct obtained when corn is processed into ethanol for your car or corn syrup. It is a traditional ingredient in cattle feed. You can read about it here. Gluten has also been associated with increased urinary tract stones in dogs. (ref)
Animal digests, meat and bone meal are the products of rendering plants and slaughterhouses. There is no telling what their oxalate content might be. But a lot of USDA condemned livers and organ meats, the carcass parts containing the most oxalate, end up in the brew. (ref 1, ref 2) That is because up to 78% of pig livers are condemned due to roundworm parasite scars.(ref)
Cats have not experienced as dramatic an increase in oxalate urinary tract stones as dogs have. Interestingly enough, the percentage of animal protein in commercial cat foods has not decreased as dramatically as it has in many dog food brands.
Veterinarians would like to keep as much calcium out of your pet’s urine as possible. A common diuretic, Lasix (furosemide) increases the calcium content of urine. Most dogs receive it for chronic heart problems. If your dog is a known stone-former, perhaps your vet would consider a thiazide diuretic like Chlorthiazide (Diuril) or Hydrochlorothiazide (Hydrodiuril).
Some dogs receive steroid medications for chronic inflammatory conditions or itching. One of the minor side effects of these medications (prednisone, Dexamethasone, etc.) can be increased calcium excretion through the urine. Some dogs have no choice but to receive long-term or intermittent steroids. But any dog that can avoid it with another option, should. A similar effect can occur in dogs with Cushing’s disease that produce to much of these compounds on their own.
Supplements containing vitamin C, excessive vitamin D or excessive amounts of calcium should probably not be given to dogs that have a tendency to form calcium oxalate urinary tract stones.
Diets designed to prevent struvite urinary stones appear to, on occasion, make pets more susceptible to oxalate stones. There was a time when these diets were formulated to produce a markedly acidic urine. When oxalate stones began to increase in frequency, these diets were reformulated to come closer to a neutral pH. Today, it is more likely that dogs that develop oxalate stones on those diets just aren’t drinking enough.
Some veterinarians think of oxalate stones as the “little white dog” syndrome. That is not true, but Bichon Frise develop more than their share of calcium oxalate urinary tract stones. More than half of the calculi this breed develop are the struvite kind. But calcium oxalate and mixed stones form most of the rest. As in all dogs, males are more likely to form stones and for those stones to be oxalate. They also have a sad tendency to reoccur in this breed. There are no special ways to protect Bichons from reoccurrence other than the ones I have outlined – just be very aggressive in keeping your dogs urine dilute and feeding it properly.
About 1994, human urologists became interested in a fragile bacteria that inhabited the large intestine of humans and many animals. That bacteria, Oxalobacter, was capable of destroying oxalate. In fact, oxalate was what it lived on. A study performed in 2003 appeared to indicate that humans with oxalate stone problems were less likely to have this bacteria. (ref)
One theory was that prior antibiotic use might have killed of the bacteria, making those humans more susceptible to oxalate urinary tract stones. The bacteria is also present in some dogs, you can read an article about that here.
or not the presence or absence of Oxalobacter plays a part in oxalate
calculi formation in humans or dogs remains unknown. Some studies suggest
it might (ref)
It may turn out that some of my suggestion are unnecessary and that some are ineffective; but until veterinarians better understand why some dogs form calcium oxalate stones on one diets and lifestyle, while others with that same diet and lifestyle do not, this is the best advice I can give you.