Today's Veterinary Practice

NOV-DEC 2015

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tvpjournal.com | November/December 2015 | ToDay's VeTeriNary PracTice acVN NuTriTioN NoTes Peer reviewed 73 Feline struvite uroliths include the component ammonia; protein sources contain both phosphorus and nitrogen, which contribute to struvite formation. Therefore, lower protein diets may be associated with reduced sterile struvite risk in cats. 20 struvite crystals, in the absence of uroliths, are rarely an indication for dietary modifcation. Calcium oxalate urolith recurrence was historically managed with reduced dietary protein given suggestions that protein promotes calcium excretion. However, higher levels of dietary protein reduced risk in dogs and cats, which may be due to increased water intake, urine output, and phosphorus excretion. 20-22 Cystine uroliths form in dogs with a genetic defect in the renal tubules. Protein restriction reduces cysteine, but animals may also have increased loss of other amino acids and carnitine; 23 therefore, defnitive recommendations are not available. Urate uroliths are a product of abnormal purine metabolism, and urate urolithiasis is prevented by purine, rather than protein and amino acid, restriction. While the purine concentration of most commercial diets is not reported, therapeutic diets for urate stones generally restrict dietary purine. Feline lower urinary tract disease is associated with several conditions, and the role of protein is unclear for many of them. However, some authors now recommend moderate to high protein diets (> 75 g/1000 kcal) because they increase water intake, urine production, and urine acidifcation. 24 Renal Disease Blood urea nitrogen (BuN), an unreliable marker of glomerular fltration rate (GF r), is infuenced by dietary protein because ammonia is liberated during amino acid processing; then it is converted to BuN, a nontoxic product, in the liver. urea itself does not contribute to renal disease but rather serves as a marker of uremic toxins. High protein diets increase BuN in both healthy animals and those affected by kidney disease; therefore, protein restriction for canine and feline renal disease is a well-accepted practice. However, the optimal amount of protein to feed animals with either kidney disease or proteinuria is unknown, and there is no substantial evidence that protein is directly toxic to renal tubules in dogs as it appears to be in humans and rats. 25 Protein content of a pet food is correlated with dietary phosphorus concentration, and some proteins contain more phosphorus per unit of protein than others (Table 3, page 74). Hyperphosphatemia reduces survival in animals with renal disease and is associated with renal secondary hyperparathyroidism; 26,27 therefore, in dogs with experimental kidney disease, diets containing elevated protein, but reduced phosphorus, were as benefcial as those with reduced protein and phosphorus. 28 Commercial renal diets provide more protein (25–55 g/1000 kcal for canine diets) than the recommended allowance for adult dogs (ie, > 25 g/1000 kcal). 2 • When consumed in appropriate amounts, they should not cause amino acid defciencies. • Dogs and cats fed these diets have median survival times 2× greater than those fed maintenance diets. 26,29,30 However, diets also contain reduced phosphorus and other modifcations compared with maintenance diets. • Most renal diets, however, do not meet the aaFco standard for adult maintenance (51 g/1000 kcal) 1 and, therefore, are sold only by veterinary recommendation. Commercial maintenance foods contain added phosphorus and are, therefore, generally not appropriate for dogs and cats with renal disease. Home-prepared diets are often used to increase protein, while maintaining reduced phosphorus, when the patient's condition dictates such an approach. Some senior and other therapeutic diets have lower phosphorus concentrations (1–2 g/1000 kcal) than many adult maintenance diets, but these concentrations are still higher than those of most therapeutic renal diets (< 1 g/1000 kcal). These diets may be used in select situations. additional considerations for feeding pets with renal disease include: • renal diets lower urine protein-to-creatinine ratio by reducing protein concentration reaching the glomerulus. • These diets may cause a mild reduction in systolic blood pressure in dogs concurrently treated with benazepril. 31 • renal diets shown to prolong survival also contain omega-3 fatty acids, which can modulate GFr, 32 but it is unclear which combination of dietary factors is contributory to the positive effects.

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