Fact or fiction?
All of the following statements are believed by many veterinarians and their clients. Yet none of them are true. Which have you heard before?
1. Urinary struvite crystals represent disease and require treatment.
2. Struvite crystals require a change in diet, usually to a prescription diet like c/d, u/d, or s/d.
3. Dogs prone to forming struvite stones should be kept on a special diet for life.
4. The most important treatment for dogs with a history of struvite stones is a low-protein diet.
Here’s why these common beliefs are misconceptions.
1. The presence of urinary struvite crystals alone does not represent disease and does not require treatment. These crystals can be found in the urine of an estimated 40 to 44 percent of all healthy dogs and are not a cause for concern unless accompanied by signs of a urinary tract infection. According to the Merck Veterinary Manual (2005), “Struvite crystals are commonly observed in canine and feline urine. Struvite crystalluria in dogs is not a problem unless there is a concurrent bacterial urinary tract infection with a urease-producing microbe. Without an infection, struvite crystals in dogs will not be associated with struvite urolith formation.â€(Our emphasis.)
Whether your struvite-crystal dog has a urinary tract infection is the key question. Researchers estimate that more than 98 percent of all struvite stones are associated with infection. Failing to eradicate the original infection and prevent new bacterial infections is the main reason struvite uroliths recur. A recurrence rate of 21 percent was recorded in one study, but the risk can be significantly reduced through increased surveillance and appropriate antimicrobial treatment. In one study, dogs were infected with an experimental Staphylococcal urinary tract infection, and their infection-induced struvites grew large enough to be seen on X-rays within two to eight weeks.
2. Struvite crystals do not require a change in diet. Because struvite crystals do not pose a problem unless the dog has a urinary tract infection, there is no required treatment for crystals, including dietary changes. If the dog does have a urinary tract infection, a prescription dog food will not cure it.
If your veterinarian finds struvite crystals in the urine and suggests a diet change, you’d be well advised to find a new vet. You have to wonder how many other things he or she is misinformed about. It isn’t just a case of not keeping up with newer research; this recommendation is just plain wrong.
3. Dogs prone to forming struvite stones should not be kept on a special diet for life. Struvites almost always form because of infections, for which dogs with a history of stones should be closely monitored and properly treated. No long-term dietary change is required, nor will a special diet prevent the formation of infection-induced struvites. However, short-term changes may help speed the dissolution of stones.
4. Low-protein diets do not prevent stone formation. A low-protein diet can speed the dissolution of struvite stones -when accompanied by appropriate antibiotic treatment -but it is not necessary for the prevention of struvite formation in dogs who are prone to this problem. For almost all dogs, controlling infections will prevent more stones from forming.
The lowdown on low-protein
Several prescription dog foods are marketed as a treatment for struvite crystals and struvite stones. These are called calculolytic foods or diets, and nearly all of them are severely protein-restricted, phosphate-restricted, magnesium-restricted, highly acidifying, and supplemented with salt to increase the patient’s thirst and fluid consumption.
While a low-protein diet is not required to dissolve struvite stones, it can speed their dissolution (when accompanied by appropriate antibiotic treatment). Protein provides urea, which bacteria convert or “hydrolyzeâ€into ammonia, one of the struvite building blocks. However, this approach is not a long-term solution and will not prevent the formation of infection-induced stones. Feeding a low-protein diet to an adult dog to help dissolve stones is acceptable for short periods. Because they are not nutritionally complete, however, low-protein foods are harmful to adult dogs if used for more than a few months, and they should never be fed to puppies.
If stones are not present, there is no reason to feed a low-protein diet. According to Dr. Chew, “No studies exist to show that a specific diet is helpful for the prevention of infection-related stone development.â€
In general, the benefits of a meat-based diet far outweigh the risks posed by protein’s ammonia generation. Plus, by feeding your dog a home-prepared diet of fresh ingredients, you can provide food that is higher in quality and much more to your dog’s liking than diets that come out of cans or packages.
Other prescription pet food strategies -such as keeping the diet low in fiber so that fluids are not lost through the intestines, using highly digestible ingredients for the same reason, and increasing the dog’s fluid intake by adding salt to the diet -can be better accomplished with a home-prepared diet and management techniques that encourage the dog to drink more water. The more concentrated the urine, the more saturated it becomes with minerals that can precipitate out, so extra fluids, which dilute the urine, reduce the risk.
Urinary acidifiers are not used to dissolve or prevent stones caused by urinary tract infections, since acidification does not help while an infection is present.