Today's Veterinary Practice

TVP_JUL-AUG2018

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PEER REVIEWED 16 JULY/AUGUST 2018 todaysveterinarypractice.com while providing adequate protein to support albumin production 1,3 and maintain body weight. 3 Phosphorus While there is still much to learn regarding the need and extent of protein restriction that is optimal for dogs with CKD, the need for phosphorus restriction is less controversial. As the kidneys retain phosphorus, the parathyroid gland is stimulated to release parathyroid hormone (PTH) to increase renal phosphorus excretion. However, PTH also stimulates the release of phosphorus from bone, which exacerbates hyperphosphatemia. In addition, calcitriol deficiency occurs secondary to decreased renal production of 1-α-hydroxylase and hyperphosphatemia. This ultimately leads to calcium deficiency and increased PTH production. Studies have shown that reducing phosphorus in the diet reduces hyperphosphatemia and the sequela of renal secondary hyperparathyroidism. 10,11 The importance of phosphorus restriction was demonstrated in a study in which 24 dogs with induced kidney disease were fed a diet with 32% protein dry matter with and without phosphorus restriction over 2 years. Dogs on the high- phosphorus diet had a lower survival rate (33%) than the restricted-phosphorus group (75%). 11 OTHER NUTRIENTS Other nutrients to consider in dogs with renal disease are sodium, potassium, and omega-3 fatty acids. Sodium restriction has been recommended as a method to combat hypertension associated with CKD. However, studies demonstrating that sodium reduction improves hypertension are lacking in dogs. Hypokalemia is a well-recognized consequence of renal disease in dogs, and most prescription renal diets have moderately high levels of potassium. Although it is more common in cases of acute kidney injury, some dogs with CKD can become hyperkalemic and may need a potassium-restricted homemade kidney diet formulated by a board-certified veterinary nutritionist. Omega-3 fatty acids—notably eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)— competitively inhibit the formation of proinflammatory leukotrienes and prostaglandins by omega-6 fatty acids. Diets high in omega-3 fatty acids have been shown to reduce glomerular capillary pressure and proteinuria and to abate the decline of glomerular filtration rate in dogs with experimentally induced CKD. 12 A dosage of 40 mg/kg EPA combined with 25 mg/kg of DHA q24h has been recommended for dogs with CKD. 13 This equates to approximately 1 g of EPA and DHA per 1000 kcal of diet when fed at 1.4 times resting energy requirements for adult maintenance. Some foods are supplemented with high concentrations of the omega-3 fatty acid alpha-linolenic acid (ALA). While this is an essential fatty acid for dogs, the conversion of ALA to EPA and DHA is poor and consideration of omega-3 fatty acid doses should not be based on ALA concentrations. ADDITIONAL CONSIDERATIONS Most veterinarians know that renal diets are a critical part of managing CKD; however, several factors can limit the use of these diets. Although renal diets are often highly palatable, as renal failure progresses, animals tend to become hyporexic. It is important to minimize food aversion as much as possible by avoiding renal diets when patients are nauseous or stressed in the hospital setting. As a dog becomes more averse to eating, it may be necessary to try different flavors or brands or to have a homemade diet formulated by a nutritionist. If a patient is unable to meet its energy requirements, a feeding tube may be useful for supplying calories, medications, and/or fluids. Homemade diets can also be used for clients opposed to feeding conventional pet foods or if a patient has multiple diseases that cannot be managed with a commercial renal diet (e.g., a dog with CKD and pancreatitis requiring a low-fat diet). While homemade diets can be used for managing CKD in dogs, a board-certified veterinary nutritionist should formulate them. SUMMARY There is still much to learn about the nutritional needs of dogs with CKD. While the combination of moderately low protein, low phosphorus, moderate sodium, and moderately high potassium and EPA/ DHA is proven to reduce uremia and extend the lifespan of dogs with CKD, controversy remains regarding the optimal dietary protein concentration for dogs with this disease. Dogs with early stages of CKD will likely tolerate less protein restriction than dogs with severe azotemia. In addition, hyporexia

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