Chronic Kidney Disease (CKD) is a prevalent condition, particularly in older cats, and is a common cause of mortality. It is a progressive condition caused by decreased kidney function or renal insufficiency. While there is no cure for CKD, nutritional management, along with other treatments, plays a crucial role in slowing its progression and enhancing the quality of life for affected cats. This article provides comprehensive guidance on feline renal diets, covering various aspects from understanding CKD to practical feeding strategies.
Understanding Chronic Kidney Disease in Cats
CKD is triggered by a loss of nephron function, potentially due to a disease, an injury, or an inherited condition. Kidneys play a vital role in maintaining overall health. They control water balance, excrete byproducts of protein digestion, and regulate potassium and phosphorus levels through urine. In cats with CKD, the kidneys fail to perform these normal functions. Veterinarians use a scoring system called IRIS (International Renal Interest Society) Stage to rank the severity of kidney disease on a scale of 1-4, with 1 being minor and 4 being very serious.
Common Signs and Diagnosis
Early warning signs of CKD can be vague and are shared by other diseases, including increased thirst (polydipsia), more urine production (polyuria), decreased appetite, loss of weight, vomiting, lethargy, and an unkempt hair coat. In the early stages of CKD, it is very common for cats to show no obvious clinical signs, as their body is able to compensate for the decrease in kidney function. As the kidneys lose their ability to concentrate urine effectively, cats may begin to urinate greater volumes and drink more water to compensate.
Diagnosis involves blood tests and urinalysis. Blood tests can determine the concentration of three important waste products normally filtered by the kidneys: blood urea nitrogen (BUN), creatinine, and symmetric dimethyl arginine (SDMA). Creatinine has historically been recognized as the most specific indicator of kidney function, but this test has some limitations. SDMA concentrations are less affected by dehydration and muscle mass and also rise earlier in the progression of CKD. In a urinalysis, a veterinarian will consider the concentration of the urine (urine specific gravity, or USG), its pH, and the presence of blood cells, bacteria, and other cells that generally should not be found in feline urine, all of which provide important information regarding the health of a cat’s kidneys. A low urine specific gravity, indicating poorly concentrated urine, can be one of the earliest indicators of CKD in the cat. Urine protein/creatinine ratio, or UPC ratio, tests for protein loss through the kidneys and can be very important in determining the severity of disease. It is also important to culture a urine sample to rule out the possibility of bacterial infection of the urinary tract in suspected cases of CKD.
Key Principles of Feline Renal Diets
Kidney diets are designed to minimize the impact of CKD on cats. Veterinarians don’t know what causes chronic kidney disease, but we know feeding a special diet helps cats with CKD maintain quality of life. In cats with CKD, kidney diets have been shown to be superior to regular adult cat food in limiting episodes of illness and death related to chronic kidney disease. These specially formulated diets aim to support kidney function and overall health through several key modifications:
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- Low Phosphorus: Phosphorus restriction, independent of other nutritional factors, delays progression of CKD; thus, it is a vitally important nutrient, if not the most important, with regard to nutrition for patients with renal disease. High dietary phosphorus may cause kidney damage in otherwise healthy adult cats, particularly when provided in highly bioavailable forms and when the calcium-to-phosphorus ratio is low. Phosphorus is the most important mineral in its pathogenesis and morbidity. Therapeutic kidney diets typically have less phosphorus than normal diets to compensate for the reduced kidney function.
- Reduced Protein: The diets also contain highly digestible protein in reduced amounts to decrease the demands of protein digestion byproduct excretion. While lower in protein, these diets are often highly digestible, and the provided protein is of high quality, meaning that amino acid composition and ratios approximate the cat's requirement. This allows for maximal utilization of amino acids to minimize endogenous protein catabolism, amino acid oxidation and protein fermentation in the colon.
- Increased Potassium: These diets have more potassium than a normal diet to compensate for the reduced kidney function. Hypokalemia is common in cats with CKD, and diets formulated for CKD may provide supplemental potassium beyond that added to maintenance diets. Maintaining the plasma potassium concentration in the middle or upper half of the laboratory reference range is recommended.
- Low Sodium or Reduced Sodium: The sodium content of therapeutic kidney diets varies widely.
- Increased Non-Protein Calories: To maintain energy.
- Extra B Vitamins: Veterinary therapeutic diets for cats with kidney disease are typically supplemented with B vitamins.
- Omega Fatty Acids: Omega fatty acids to reduce inflammation & maintain kidneys
- More Fiber.
- More Water: Wet (canned) food is likely better than dry food because it provides more water.
Practical Feeding Strategies
In general, cats are not fans of change-but if the kidney diet is going to help, they need to eat it. Don’t hesitate to try different brands of kidney food and introduce the new food slowly. Use a separate plate for the kidney diet and only serve a small portion until your cat is readily eating the kidney food. Then increase the portion size.
Transitioning to a Renal Diet
Make the diet change gradually. At first, you may need to mix your cat’s current diet with the new one. It is important to make a gradual transition to a therapeutic diet and to consider food temperature, texture, and flavor.
Enhancing Palatability
- Gentle warming of wet diets and adding warm water to dry diets can also help cats stay interested in their food. Warm the food to bring out the flavor. Most cats prefer food served at body temperature.
- Make low sodium chicken broth. Boil or microwave a piece of chicken with water and save the broth. Do not skim off the fat. Thighs and legs work well to make broth. Cut up some small pieces of the chicken to include in the broth. This broth can be used to flavor any of the renal diets and make them more palatable.
- Flavor the foods with low sodium canned tuna fish. This product is made for human consumption and available in most grocery stores. Star Kist tuna is one of the low sodium brands
Hydration is Key
A cat with CKD will need access to lots of fresh water. Your cat must drink lots of water. Give your cat fresh water every day. Do not add water to replace that which has evaporated from your cat’s bowl. Water is the most important part of this treatment. We combat this problem with fluids administered under the skin at home.
What to Do If Your Cat Refuses the Diet
It is more important that your cat eat something than to eat very little of a prescribed new renal diet that it does not like. Never try to fast (starve) your cat into eating a prescription diet.
Monitoring and Adjustments
Serial monitoring of these patients is ideal and treatment should be adapted according to the response to treatment.
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Regular Veterinary Check-ups
Your cat’s veterinarian will test a urine sample to make sure there is not an infection or protein leaking from the kidneys.
Home Monitoring
Because the kidneys struggle to control water balance, cats can easily become dehydrated.
Additional Considerations
Managing High Blood Pressure
High blood pressure is common in cats with CKD. Your veterinarian will measure blood pressure as part of a clinical evaluation. If your cat is hypertensive, they will prescribe daily medication to control high blood pressure.
Homemade Diets
Your veterinarian may be able to provide recipes for special diets that you can prepare in your home for your cat. Some of these are quite tasty and successful. Referral to a board-certified veterinary nutritionist is recommended for formulation.
The IRIS CKD Staging System
The International Renal Interest Society, or IRIS, has developed a staging system to categorize cats with CKD based on these testing parameters. It is important that the staging occurs when the cat is well hydrated and stable, as elevated values in a dehydrated or sick cat could make it appear that they are experiencing a higher stage of disease than they truly are. With this in mind, appropriate staging can provide useful treatment and management strategies for owners and veterinarians, as well as prognostic information based on the severity of disease.
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Therapeutic kidney diets vs phosphate binders
The dilemma many clinicians therefore face is whether to prescribe a therapeutic veterinary kidney diet and risk poor intake with resultant decreased muscling and body condition, or to opt for an 'over-the-counter' commercial maintenance diet with or without a phosphate binder such as aluminium hydroxide.
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