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TVP_JUL-AUG2018

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PEER REVIEWED 14 JULY/AUGUST 2018 todaysveterinarypractice.com Most studies evaluating protein restriction in dogs with CKD are based on the remnant kidney model, which induces renal failure through removal of large amounts of renal tissue or ligation of the renal blood supply instead of naturally occurring disease. 2,3 Moderate protein and phosphorus restriction (35 g and 750 mg per 1000 kcal, respectively) reduced morbidity and mortality in beagles with induced CKD while high protein intake (110 g/1000 kcal) worsened clinical signs and increased death rates. Low-protein diets containing 17 g protein/1000 kcal lowered plasma protein and albumin concentrations. 2,3 Unfortunately, it is difficult to determine the true impact of dietary protein in these studies, as the diets varied in caloric density, phosphorus and sodium content, and protein digestibility. Proteinuria The intact nephron hypothesis states that once a critically low mass of nephrons is reached, the remaining nephrons hypertrophy and signal the need for increased blood flow, glomerular filtration rate, and pressure. The chemical and electrical selective barriers of the glomeruli are then impaired, and increased levels of protein pass into the filtrate. Eventually the tubular reabsorption of protein is overwhelmed, and tubular cells begin to secrete inflammatory mediators that further damage the kidneys. 5 Protein-restricted diets have been shown to reduce glomerular damage and urinary protein concentrations in dogs with hereditary nephritis. 6,7 The amount of protein restriction needed to mitigate renal damage secondary to proteinuria in dogs is unclear. For example, when dogs with nephritis ate diets containing 72 or 33 g of protein per 1000 kcal, mean urine protein:creatinine ratios were 4.7 and 1.8, respectively. However, dogs on the lower-protein diet also had reductions in albumin and body weight. 7 A more recent study evaluated a renal diet in combination with angiotensin- converting enzyme inhibitors in proteinuric dogs with CKD and saw no change in albumin or body condition score over a 5-month period. 8 Careful consideration of dietary protein intake, including current protein intake, is required in dogs with proteinuria. For example, a proteinuric dog on a high-protein diet may have substantial improvement if dietary protein intake is reduced by 25% to 50%. Careful monitoring and assessment of other clinical signs are needed to balance protein losses and renal damage in these patients. Dietary Protein Requirements When assessing the protein content of a diet, it is important to remember that animals require amino acids rather than protein. Feeding high-quality protein sources with well-balanced ratios of essential amino acids can lower overall dietary protein content while preventing protein malnutrition. It is also important to note that all diets currently marketed for management of CKD in dogs exceed the amounts of protein recommended by the National Research Council ( TABLE 1 ). 9 More studies are needed to determine whether lowering dietary protein to the level of most renal diets is critical for managing CKD, or if alterations in phosphorus or omega-3 fatty acids are providing most of the improvement seen in research studies to date. Based on the evidence currently available, diets providing approximately 35 g/1000 kcal of high-quality protein, combined with other dietary modifications, improve and prolong the life of dogs with CKD 1,2 TABLE 1 Nutrient Profile of Typical Therapeutic Diets Designed for CKD Management NUTRIENT (G/1000 KCAL) THERAPEUTIC CKD DIETS AAFCO* NRC RECOMMENDED ALLOWANCE FOR ADULT DOGS 9 Protein 31–41 45 25 Fat 40–62 14 14 Phosphorus 0.5–0.8 1.0 0.75 Potassium 1.1–2.3 1.5 1.0 Sodium 0.4–1.2 0.2 0.2 EPA + DHA 0.4–1.2 n/a 0.1 *2017 American Association of Feed Control Officials (AAFCO) adult maintenance minimum. DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; n/a, not available; NRC, National Research Council.

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