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renal disease in dogs

By Ness Bird - Nutrition Adviser and RVN Cert CFVHNut ©

Arden Grange regrettably do not manufacture products specific to the dietary management of renal disease. The production of veterinary diets is highly specialised, requiring extensive clinical trials.


Renal 1
introduction

The severity of renal disease is normally graded using the International Renal Interest Society’s scale based on fasting blood creatinine and SDMA concentrations. Creatinine is a waste product excreted by the kidneys when muscle tissue breaks down. SDMA (symmetric dimethylarginine) is a compound formed as the body’s cells metabolise and rearrange their protein content. Stage 1 indicates the mildest dysfunction, whilst stage 4 indicates the most serious [IRIS, 2019].

Dogs with stage 1 renal insufficiency (very mild) may eat a suitable regular diet, providing it is highly digestible and does not supply overly high levels of protein, phosphorous and sodium. It is also important that there are no complications such as a concurrent condition requiring special nutritional management. Renal disease is often progressive, and close monitoring is required so that further dietary changes can be implemented if necessary in the future.

Whilst veterinary diets are not always popular due to their high cost and low rating by some opinion-based pet food critics, dogs with stage 2 - 4 kidney disease will usually benefit more from a product tailored specifically to their condition than a regular pet food. Regular diets must meet the nutritional requirements of normal dogs, so although you may be able to find some products with somewhat lower levels of pertinent nutrients than others, they cannot be restricted to the same degree as those of a veterinary diet.



limitations of veterinary diets

A veterinary diet may be the gold standard for dogs with more advanced renal problems, but what happens if you are finding the cost prohibitive, or your dog can’t or won’t eat it?


If you have tried and struggled with more than one renal diet, there are alternatives to veterinary products which are discussed later. Even the staunchest proponents will agree that any nutrition is better than no nutrition, especially if inappetence, weight loss and/or digestive problems associated with an unsuitable veterinary diet are negatively affecting your dog’s quality of life. In cases of severe inappetence, tube feeding may be necessary.



why diet is so important

Acute kidney damage (e.g. from ingesting pesticides) can be reversible if is it diagnosed at its earliest stage and treated immediately, but in cases of chronic renal insufficiency, improvement is only rarely possible. Clinical signs are not normally evident until there is around 70-85% loss of functional capacity, by which time the damage is irreversible. Therefore, the aim is to stabilise kidney function and slow further progression of the disease. Renal diets can help to achieve this since they are specially formulated to lighten the workload of the ailing kidneys, as well address secondary metabolic changes.



why the need for restricted protein, phosphorous and sodium?


Protein
When the kidneys are not working properly, the waste products of protein metabolism - ammonia, urea, uric acid and creatinine – (which would normally be efficiently excreted via the urine) can build up to toxic levels in the blood. Reducing the protein intake may reduce the amount of waste. As the kidneys also filter useful substances back into the blood, this can reduce the amount of protein itself from entering them, further lessening their load.

Another consideration is that protein-rich ingredients such as meat and fish are generally rich in phosphorous (which requires restriction too), and promote a more acidic urine (the urine of dogs with renal disease is often already too acidic).

However, protein should only be moderately restricted because an insufficient supply results in protein malnutrition and loss of lean body mass, which reduces the dog’s strength and immunity. Furthermore, protein metabolism is less efficient in senior dogs, and they therefore need enough to maintain their reserves and maximise renewal and replacement. There have been many studies regarding protein restriction in the progression of chronic kidney disease in dogs, but further investigation is still required [Cline. M, 2015].

Protein restriction is however recommended for dogs with proteinuria (protein in the urine) secondary to glomerular disease (a type of kidney disease affecting the glomeruli which filter plasma) [CGN IRIS, 2013]. It is also beneficial for dogs with hereditary nephritis, as research has shown that this reduces structural damage to the glomeruli and delays the progression of renal failure [Valli et al, 1991].

At present, the degree of protein reduction is generally dependent on the individual’s diagnostic test results and symptoms, and it is also relative to the protein intake provided by the original diet. It is, however, undebatable that the protein eaten by a dog with renal insufficiency is highly digestible and bioavailable, meeting all amino acid requirements. Poor quality proteins give the kidneys a lot of work for limited, if any, nutritional value and therefore foods comprised mainly of indigestible protein (e.g. rawhide) should not be fed.

Phosphorous
Phosphorous restriction is extremely important because it can slow the progression of renal disease. When filtration is compromised, there are greater circulating levels of phosphorous in the blood. This can then cause a complex endocrine condition called renal secondary hyperparathyroidism and calcitriol (an active form of vitamin D normally made in the kidney) deficiency. Resultant complications include soft tissue mineralisation and fibrous osteodystrophy.

Sodium
In addition to filtration and waste excretion, the kidneys are also involved in the maintenance of the body’s salt and fluid concentrations and help to control blood pressure. Although high sodium diets can increase blood pressure, which may contribute to the progression of renal disease, there is currently no evidence to support that reducing sodium can decrease hypertension in dogs. However, mild sodium restriction is a typical feature of renal diets since it helps avoid the accumulation of high levels when sodium excretion by the diseased kidneys is less efficient [Fascetti & Delaney, 2012]. Sodium should not be suddenly and dramatically restricted since this can cause dehydration, and the ailing kidneys also need time to adjust to a different level.



units of measurement


Nutrient levels expressed as percentages (on a dry matter basis) for dogs with renal disease are typically as follows: -  

Protein 14 - 20% DM
Phosphorus 0.2 - 0.5% DM
Sodium ≤ 0.3% DM

However, it is more accurate to compare values per 1000 calories since the energy density of feeds can be highly variable.



table showing typical nutrient levels of a renal diet compared to Arden Grange products

* Figures from the ACVN’s Nutrition Notes – The Nutritional Management of Chronic Kidney Disease

Protein and phosphorous levels in the Arden Grange products are too high for dogs with Stage 2 - 4 renal disease, but these diets may be suitable for dogs with Stage 1 renal disease and no complications.

Dogs with more advanced kidney problems who will not or cannot eat a veterinary diet may be fed a regular diet (providing it is not overly rich in any of the aforementioned nutrients and meets certain other criteria – please refer to Benefits later in the fact sheet) alongside a phosphorous binding drug such as Ipakitine or Pronefra.

One possible compromise may be to feed some veterinary diet with some normal food, with the longer-term goal of slowly increasing the renal feed and decreasing the regular diet.

Note: In some cases both a veterinary renal diet AND phosphorous binder may be recommended by the patient’s vet, depending on the plasma phosphate concentration.

As with any dog under veterinary care for a nutritionally responsive medical condition, we advise asking your vet’s professional opinion as to the suitability of any diet if it is not one that he/she has suggested.



feeding dogs with stage 1 renal disease
If your vet agrees, Arden Grange Light (ideally fed soaked) may be a suitable option as it is our lowest protein diet. It is also our lowest phosphorous dry food, and sodium falls just on the cusp between the mildly and moderately restricted categories. Please note however that the low-fat content of this product may contraindicate it for inappetent or underweight dogs. A complete wet food such as the Arden Grange Partners Chicken may be a consideration, especially if your dog is not a good drinker and/or will not accept soaked dry food. A combination of wet and dry food is often suitable.


maintaining good fluid uptake is critical because of the reduced capacity to concentrate urine and the risk of dehydration.
  • Feeding wet food (which typically contains 60% + moisture compared to around 8% in a commercial complete dry dog food).
  • Soaking dry food (for about 1/2 hour prior to serving and then topping up with a little more water once the moisture has been absorbed). Uneaten wet, fresh or soaked dry food must be discarded, especially in hot weather, to avoid bacterial and insect contamination.
  • Using a canine water fountain. Many dogs find these more interesting that water from a bowl.
  • Providing several drinking stations. This can be useful for opportunistic drinkers, who may not actively seek out a bowl if they are not particularly thirsty, but if they are passing, they might well take a drink on the way through to wherever they are going. Also make sure the water is not too cold.
  • Using filtered water. Dogs have special taste buds at the tip of the tongue for water which are very sensitive, and tap water is not always appealing, hence why they often prefer to drink from puddles! Some filters can also reduce metal content of tap water


Arden Grange benefits

1. Bioavailable protein at a moderate level from diverse sources - easily utilised and provides an excellent amino acid profile.
2. Chicken oil as the primary fat source - very palatable and highly digestible.
3. Krill - an excellent source of Omega-3 DHA & EPA - these essential fatty acids may help reduce blood pressure within the capillaries of the glomerulus (part of the nephron, the functional unit of the kidney.
4. Digestible complex carbohydrates - providing an efficient source of energy, helping reduce gluconeogenesis (sugar production) from protein and fat. Glucose is the only energy source used by the medulla of the kidney, and it is much more easily manufactured from carbs than non-carbs.
5. Moderate level of soluble fibre - to reduce colonic acidity and trap nitrogen.
6. Prebiotics FOS & MOS - which may reduce ammonia concentrations within the intestine. Increased fermentation leads to higher amounts of nitrogen converted into bacterial protein (Howard et al, 2000). 
7. Antioxidant plant extracts & antioxidant vitamins - which may help reduce renal oxidative stress by decreasing reactive oxygen species generation [Brown. S, 2008].



home-prepared diets

A home-prepared diet can be useful in the short-term to encourage inappetent dogs to eat, and lower phosphorous items which are safe for dogs to consume include chicken thigh meat, egg whites, cottage cheese, rice and pasta. However, if you are intending to cook for your dog long-term, you should ideally use the service of a board-certified veterinary nutritionist to devise a suitable diet to avoid nutritional imbalances. It can be tricky enough getting nutrient levels right for a dog with normal requirements, and a scientific study of home prepared canine and feline diets (both raw and cooked) showed that all 80 of the canine diets were deficient in at least one nutrient. The most common being iron, vitamin E, zinc, calcium, copper, choline, riboflavin, thiamine and vitamin B12.  [Pedrinelli et al, 2017].

One useful resource is Balance IT®, which provides free online formulation software created by Sean Delaney, DVM, MS, Diplomate of the American College of Veterinary Nutrition (DACVN), Davis Veterinary Medical (DVM) Consulting, Inc. [Balanceit.com, 2019]. To be able to view the renal diets, your veterinary surgeon’s approval is required. The accompanying nutritional supplements recommended are shipped from the USA, but delivery costs are reasonable.



a note about puppies

The nutritional management of renal disease in puppies is highly complex, and beyond the scope of this article, since phosphorus restriction can impair normal bone development. Depending on the individual, it may be necessary to either prioritise bone development or delay the progression of kidney dysfunction.



References
IRIS (2019). IRIS Kidney - Guidelines - IRIS Staging of CKD . [online] Available at: http://www.iris-kidney.com/guidelines/staging.html [Accessed 7 Jan. 2020].

Zooplus (2020). Renal Dog Food for Dogs with Kidney Problems | zooplus UK . [online] Available at: https://www.zooplus.co.uk/shop/veterinary_food/dog_vet_food/kidney_heart [Accessed 7 Jan. 2020].

Cline, M. (2015). Nutritional Management of Chronic Kidney Disease in Cats & Dogs | Today's Veterinary Practice . [online] Today's Veterinary Practice. Available at: https://todaysveterinarypractice.com/acvn-nutrition-notesnutritional-management-of-chronic-kidney-disease-in-cats-dogs/ [Accessed 7 Jan. 2020].

IRIS Canine GN Study Group Standard Therapy Subgroup, Brown S, Elliott J, et al. Consensus recommendations for standard therapy of glomerular disease in dogs. J Vet Intern Med  2013; 27 Suppl 1:27-43.

Valli VE, Baumal R, Thorner P, et al. Dietary modification reduces splitting of glomerular basement membranes and delays death due to renal failure in canine X-linked hereditary nephritis. Lab Invest 1991; 65(1):67-73.

Fascetti, A. and Delaney, S. (2012). Nutritional Management of Chronic Renal Disease . [online] UC Davis School of Veterinary Medicine. Available at: https://www.vetmed.ucdavis.edu/hospital/animal-health-topics/chronic-renal-disease [Accessed 7 Jan. 2020].

Howard, M., Kerley, M., Sunvold, G. and Reinhart, G. (2000). Source of dietary fiber fed to dogs affects nitrogen and energy metabolism and intestinal microflora populations. Nutrition Research , 20(10), pp.1473-1484.

Brown, S. (2008). Oxidative Stress and Chronic Kidney Disease. Veterinary Clinics of North America: Small Animal Practice , 38(1), pp.157-166.

Pedrinelli, V., Gomes, M. and Carciofi, A. (2017). Analysis of recipes of home-prepared diets for dogs and cats published in Portuguese. Journal of Nutritional Science, 6.

Secure.balanceit.com. (2019). BalanceIT.com. [online] Available at: https://secure.balanceit.com/recipegenerator_ver4/index.php?rotator=EZ [Accessed 26 Jun. 2019].