Diets have been a mainstay of chronic renal failure treatment in pets for decades. Considerable research has been done on which dietary factors influence renal disease.
Restricting dietary protein, based on the marked exacerbation of signs of uremia associated with feeding high protein diets, has been a cornerstone of renal diets.
However, certain species, especially cats, are obligate carnivores and require higher-protein diets. Significant protein restriction can result in protein-calorie malnutrition. There are many other potential positive effects of renal diets, including increased potassium concentrations, decreased phosphate levels, decreased sodium and improved acid-base status.
Scientific publications support the positive effects of dietary management of CRF in dogs and cats with spontaneous renal disease. In one study of 50 cats, 29 were fed a veterinary renal diet and 21 were not because of lack of compliance (by cat or owner).
The veterinary diet led to lower phosphate, urea and PTH concentrations as well as more than doubling the lifespan of the patients (Elliott J. Rawlings, JM, et al. "Survival of Cats With Naturally Occurring Chronic Renal Failure: Effect of Dietary Management." Journal of Small Animal Practice 41;235-242:2000).
Renal Beats Maintenance
A retrospective study compared 175 cats on maintenance diets to 146 cats on various renal diets. Survival time was seven months for the conventional diets and 16 months for the renal diets (Plantinga EA, Everts H., et al. "Retrospective Study of the Survival of Cats With Acquired Chronic Renal Insufficiency Offered Different Commercial Diets." Veterinary Record 157;185-187:2005).
A randomized clinical trial in dogs showed similar results.
Dogs fed a renal diet took longer to develop a uremic crisis, had less azotemia and longer lifespan (Jacob F., Polzin D.J., et al. "Clinical Evaluation of Dietary Modification for Treatment of Spontaneous Chronic Renal Failure in Dogs." JAVMA 220;1163-1170:2002).
Researchers from the University of Minnesota, University of Tennessee and Hill's Science and Technology Center carried out a double-masked, randomized clinical trial in 45 cats with spontaneous renal failure (Ross S, Osborne C, et. al. Clinical evaluation of effects of dietary modification in cats with spontaneous chronic renal failure. JVIM 19;433:2005).
The cats received either a renal diet or a maintenance diet. The renal diet was modified in protein, phosphorus, sodium and lipid composition in comparison to the maintenance diet. The cats were evaluated every three months for two years.
The cats receiving the renal diet had lower serum urea concentrations and higher bicarbonate values. Cats on the renal diet also had fewer instances of a uremic crises and a reduction in renal and all-cause mortality.
This study is consistent with others that have been carried out, though these studies in cats were not randomized.
Water Intake and Feeding
Cats often do not consume large quantities of water and tend to have very concentrated urine. It would be preferable in some disease states, such as feline interstitial cystitis, to have cats consume larger quantities of water. A variety of techniques have been recommended to achieve this goal, including adding salt to their food.
Researchers from University of Liege in Belgium investigated whether changing feeding frequency and/or energy intake changed water intake (Lhoest E., Leemans J., et al. "Effects of Feeding Frequency on Water Intake in Cats." JVIM 19;476:2005).
Twenty-four cats were included in the study. The cats had access to ad libitum water and received the same diet.
After two weeks on a diet protocol, the next week was used to obtain values. The cats were fed either once, twice or three times daily. The cats received either 71 (low energy) or 91 (high energy) kcal/kg body weight per day.
Water intake increased from 72 + 10 when the cats were fed once daily to 95 + 6 ml/day when the cats were fed three times daily. Feeding more calories led to more water intake.
This study shows that feeding multiple meals is an effective way to increase water intake in cats. Feeding more calories will also achieve this goal, though weight gain may occur in this scenario.
Tracheal Collapse, Obesity
Tracheal collapse is a common diagnosis in small-breed dogs. In acquired disease, the tracheal rings become too soft and collapse. The disease can be asymptomatic or debilitating. A variety of factors can play a role.
Researchers from the University of Murcia in Spain investigated 21 dogs with radiographically confirmed tracheal collapse (Talavera J., Fernandez del Palacio M.J., et al., "Clinical Findings and Associated Conditions in Dogs With Radiographically Diagnosed Tracheal Collapse: 21 Cases." JVIM 19;449:2005).
Of these, 38 percent were Yorkshire terriers. The most common clinical sign was cough (86 percent of the dogs). Syncope occurred in a quarter of the dogs, as did noisy respiration. Chronic mitral valve disease was a concurrent problem in 20 percent. A large percentage of patients were overweight (76 percent).
Tracheal collapse is a complex problem. Several factors may play a role in the development of clinical signs including smoking in the household, underlying lower airway disease and hepatomegaly. This study shows that obesity is common in these dogs. Obesity may cause hepatomegaly, as well.
How hepatomegaly and obesity cause clinical signs is uncertain, however in obese patients with collapsing tracheas and clinical signs, it is absolutely vital to include an aggressive weight reduction program. In some cases this can result in a significant improvement in symptoms seen.
Anthony Carr, DVM, Dipl. ACVIM, is an associate professor at the Western College of Veterinary Medicine in Saskatoon, Saskatchewan, Canada.