Chronic kidney disease (CKD) is a common occurrence in our senior cat population. Increasing water intake (i.e., improving hydration status) and dietary changes have traditional been advocated for cats with CKD. Conflicting opinions exist regarding when to switch CKD cats to a renal protective type diet. Many feline specialists have recommended that nutritional management should begin when cats develop azotemia (i.e., with IRIS stage 2 and higher CKD). Other studies, including this study, suggest initiating renoprotective dietary therapy earlier (i.e., with IRIS stage 1 CKD) in order to slow progression of CDK.
Dr. Hall from the College of Veterinary Medicine at Oregon State University and Hill’s Pet Nutrition, Inc. and IDEXX Laboratories, Inc. conducted a prospective study in client-owned geriatric cats to evaluate short-term effects (i.e., up to 6 months) of a renoprotective dry food (i.e., test food) on serum symmetric dimethylarginine (SDMA), creatinine (Cr) concentrations and other renal parameters. The control group was comprised of matched (i.e., > 9 yrs, neutered, indoor only, similar age, etc.) cats and were fed owner’s-choice dry food only.
An initial enrollment of 105 cats met the inclusion criteria, and a total of 80 cats completed the 6-month study. Eighteen of 51 cats consuming the test food, and 7 of 54 cats consuming owner’s-choice foods had incomplete data or failed to complete the study. Detailed breakdown on reasons why these particular 25 cats failed to complete the study was not given.
Cats consuming test food showed statistically significant decreases in serum SDMA, Cr and BUN concentrations across time. Cats consuming owner’s-choice foods showed statistically significant increases in serum SDMA concentrations and decrease in urine specific gravity at 3 and 6 months compared with baseline (all P < 0.05).
A subset of nonazotemic (CR < 2.0/dL) cats with increased serum SDMA concentrations (SDMA > 14 indicating early renal insufficiency) was also analyzed. This included 17 cats fed owner’s-choice foods and six cats fed test food. Based on serum SDMA concentrations, of the 17 cats fed owner’s-choice foods, three improved during the course of the study (serum SDMA decreased), 13 got worse (serum SDMA increased), and one stayed the same (no change in serum SDMA). The increase in serum SDMA concentration was statistically significant (P = 0.02) for cats fed owner’s-choice foods. Of the six cats fed test food, three improved (serum SDMA decreased), two got worse (serum SDMA increased), and one stayed the same (no change in serum SDMA). Therefore, researchers suggest that a renoprotective diet should be considered as early as IRIS stage 1 CKD.
Although many changes were made to the Hill’s test diet, its nutrient content is different than what is listed on their website regarding Hill’s K/D (http://www.hillspet.com/en/us/products/pd-feline-kd-dry); Hill’s K/D dry mass percentage is protein = 30.1%, fat = 23.1%, and carbohydrate = 40.5% compared to this study's content of protein = 35.6%, fat = 17.7%, and carbohydrate = 40.8%. It is also unfortunate that these researchers chose to feed only dry food in this study, which has too high of a carbohydrate content for cats. The control group may be difficult to interpret since some of these owner’s-choice diets may also have a slightly lower protein and phosphorus content, and account for the improvement in renal parameters seen in a few of the control cats.
One of the concerns regarding commercial renoprotective diets is that cats would not eat sufficient calories to maintain weight. Although the test food had a better quality meat source than previous prescription diet from Hill’s, and the diet was spiked with essential amino acids - body condition score, muscle mass score, and 3- and 6-month body weights of the cats were not provided in this study, only initial weights. Although statistical significances were noted in this study, clinical significance in starting ISIS stage 1 CKD cats on renoprotective diets still needs further evaluation.
