Dr. Lucy L. Pinkston, D.V.M.
in this series: Nutrition
 • General nutritional guidelines
 • Large breed puppies
 • Hypoglycemia in toy breed puppies
 • Specific dietary situations
 • Dogs with kidney problems
 • Questions & Answers: 1  2
 • Bloat (GDV) & Survey vet@dog   Dogs with kidney problems
Introduction to the Urinary System: Anatomy and Function
The kidneys are responsible for filtering many toxic substances from the blood, especially the by-products of protein digestion and other nitrogen-containing compounds. They are also responsible for regulating precisely the levels of minerals and electrolytes (salt-like compounds) in the blood stream. Another very important function that is unrelated to its role in urinary function, is the production of the hormone erythropoeitin, which stimulates the bone marrow to produce red blood cells. Red blood cells carry oxygen from the lungs to the rest of the body.

There are two kidneys in the body, both located under the back-bone, close to where the last rib meets the spine. Through a number of complex processes, the kidneys filter the blood, remove certain toxins, and retain certain minerals and electrolytes. The fluid that remains is urine, which is collected in a central area of the kidney and funneled into a small tube called the ureter. The ureters (one from each kidney) run from the kidney to the bladder, which is located just in front of the pubic bone of the pelvis, and collects the urine until the quantity is sufficient for the dog to feel the urge to urinate. The urine is retained inside the bladder by a circular muscle called a sphincter, which relaxes at the same time the bladder contracts, allowing urine to exit the bladder into the urethra, which is the passageway to the outside.

Urinary problems can occur at any point along the urinary tract. Infections are very common in the bladder, especially in female dogs, whose urethra is wider and shorter than the males. Males, however, can and do get bladder infections. In intact (non-neutered) male dogs, these infections can be more difficult to treat than those of neutered males because it is easier for bacteria to stay hidden from antibiotics in the prostate, which shrinks substantially following neutering. Recurrent lower urinary tract infections (i.e. of the bladder and/or prostate) are the number one cause of kidney infections, because, with time, the infection may travel up the urethra to infect the kidneys. Although there are several other important causes for kidney function to be reduced, damage from ascending urinary tract infections is a significant cause of age-related kidney insufficiency or failure. Dogs and cats can lose up to 2/3 of their functional kidney capacity without losing any of the ability of their kidneys to do their job! After 2/3, most dogs/cats will start drinking more water to help compensate for reduced function. It is only when 3/4 of the capacity is gone, that the kidneys can no longer compensate completely and toxins and abnormal levels of minerals and electrolytes begin to build up in the blood stream.
Dietary Assistance for Dogs with Failing Kidneys:
Dietary changes for dogs with renal (kidney) insufficiency or failure may be helpful, but it is important to understand that they are not going to cure or even treat the disease itself. Diet modification merely gives the kidneys an easier job to do. It does little to help the function itself.

Because by-products of protein digestion are the main toxins that need to be excreted by the kidneys, an obvious assumption might be that all one needs to do is to cut out the protein and the kidneys wouldn't have any more hard work to do. Of course, things are never that simple. One certainly would not want to give an excessive amount of protein, but how much is too much? Dogs do have a minimum daily protein requirement, the amount of which depends on the quality of the protein being fed and on the health status of the animal. Proteins are graded on their "biologic value." High biologic value means that the protein is highly digestible, easily absorbed by the intestinal tract, and that its amino acid components (the building blocks of proteins) include all the essential types of amino acids in their optimal proportions. Egg protein and milk protein (casein) are the dietary proteins with the highest biologic value. Lean meat protein from muscle or organ meat, not meat by-products, are a close second. Normal, healthy dogs, with average activity levels, need approx. 3 - 3 1/2 gm of high-biological-value protein, "as fed," per lb. body weight per day. This translates into approximately 0.6 - 0.7 gm of dried cooked egg/lb/day. There is significant evidence, however, that the daily protein requirements actually increase slightly for dogs in chronic renal failure. Therefore, severely restricting the protein for such a dog is likely to result in protein malnutrition, in spite of the fact that the levels of blood urea nitrogen, or BUN (the primary by-product of protein metabolism) would be correspondingly lower. Typical prescription "kidney disease diets" formulated by various commercial pet food companies are designed to provide high quality protein in moderately restricted amounts (generally 0.9 gm of dry-weight protein/lb/day), while providing adequate caloric intake from non-protein ingredients. Further adjustment of the diet must be based upon the individual animal: (1) blood test evaluations of kidney function (e.g. BUN levels); (2) general appearance of the patient (e.g., muscle mass, maintenance of body weight; and (3) clinical assessment of health status. If the BUN levels are in a "good" range, but the dog is progressively losing weight, then the protein may have to be increased. Conversely, if the dog is maintaining adequate nutritional status, but the BUN is steadily climbing, then reducing the protein further may be of benefit.

Other dietary issues for dogs in chronic renal failure include (1) maintaining adequate caloric intake to keep other bodily processes functioning properly; (2) maintaining adequate levels of water soluble vitamins (B complex and vit.C); and (3) preventing excessive calcium loss because of the elevated phosphorus levels that develop secondarily in renal failure.

Caloric requirements are usually met by the addition of extra carbohydrates and fat to the diet. It is recommended that dogs receive 35 - 50 Cal./lb/day, on average, and that these amounts be tailored to meet the needs of the individual patient. The commercial kidney diets usually fulfill these requirements. To prevent excessive loss of the water soluble vitamins, supplementation of balanced B complex vitamins and Vitamin C is usually recommended. For dogs with excessive blood levels of phosphorus, a phosphorus binder such as Amphojel, Basaljel, or Alternagel, is given with each meal, in order to bind some of the phosphorus present in the food. The amounts of these supplements should be determined by the veterinarian, based on the status of the individual patient.

Kidney failure is a varied and complex disease, affecting many organ systems and affected by numerous intrinsic and extrinsic factors. Dietary management is only one factor that can affect the quality of a kidney patient's life. There are many others, which your veterinarian can discuss with you. Appetite loss, nausea, and other problems can complicate the picture and a number of symptomatic treatments can provide significant relief for a time. Fluid therapy, administered either intravenously or between the layers of the skin, can make a significant temporary improvement in the animal's clinical status. Unfortunately, most cases of chronic renal failure are cases of management, not cure. With that in mind, the "ideal treatment regimen" becomes secondary to the patient's quality of life. For example, if the dog has no appetite for the food he is "supposed" to eat, but wants something he is not supposed to have, the question arises, "Isn't it better to eat something than nothing?" If an antiulcer medication will decrease the nausea caused by excessive BUN levels, but the dog fights it bitterly, is it worth the battle? These are very difficult questions that all owners of kidney patients face. There are no easy answers, but the support of your veterinarian, the veterinary staff, and your circle of dog-friends can help you through a lot of them. Dietary management is only a portion of the bigger picture.

vet@dog mission
Dr. Pinkston and hope you find the vet@dog articles educating and thought provoking. The more information you have when taking your dog to your vet, the better. When you take your dog to the vet, it is useful to write down symptoms and questions: You will be sure to ask all your questions, and your vet will have more information in making a diagnosis.

If you have a question about a vet@dog article, or have a question about your dog, you may want to post to the i-dog message board or the i-dog e-mail discussion list. Dr. Pinkston reviews i-dog postings and responds to discussions likely to benefit a large number of dog owners.

Internet advice... and Dr. Pinkston do not offer advice on specific medical problems since any answer given without examining a dog thoroughly, in person, would be incomplete, at best. It is too easy to jump to erroneous conclusions and give unintentionally misleading advice.

If your dog has a problem that has not resolved with treatment, Dr. Pinkston highly recommends that you consult your own vet about performing additional diagnostic tests, if warranted. If your vet has already done as much as possible at that clinic, you might ask to be referred to a specialist. If that is not possible in your area, then consider getting a second opinion. Keep in mind, though, that your own vet may not realize the full extent of the problem or your concerns about it. It is always a good idea to start by explaining to your vet that a particular problem has not been resolved and that you are really worried about it.

copyright & disclaimer
Information and opinions stated are for educational purposes only, should not be used for diagnosis or treatment, and are not intended to replace advice and/or treatment provided by your veterinarian. and Dr. Pinkston disclaim responsibility for the consequences of any action you may or may not take based on this information. Please consult your veterinarian for specific advice and treatment of your dog.

Copyright 2000 Dr. Lucy Pinkston. All rights reserved.
This material may not be published, broadcast, rewritten, or redistributed.

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