The kidneys are vital organs which act as the body’s filtration system, keeping the blood clean and free of toxins. They regulate blood pressure, water consumption, pH levels, and minerals such as phosphorous, magnesium, and sodium. The nephron is the functional unit of the kidney, as the number of working nephrons decreases in the kidneys, the symptoms of kidney disease become more severe. A reduction of nephrons subsequently leads to a reduced blood filtration rate, which reduces the ability of the kidneys to filter and excrete waste products efficiently (1). When the kidneys are not functioning correctly, these waste products can build to dangerous levels in the blood, which is known as azotaemia (2).
Acute or Chronic?
| Acute Kidney Disease Symptoms | Chronic Kidney Disease Symptoms |
| Lethargy Diarrhoea Vomiting Disorientation Severe weakness Difficulty urinating | Excessive thirst Excessive urination Reduced appetite Weight loss Urinary infections Vomiting and diarrhoea |
Acute Kidney Disease (AKD)
AKD is typically short term, and often rapidly diagnosed due to its sudden onset of symptoms. Correct medical and nutritional intervention can see dogs fully recovered (3). It can be caused by a restriction of blood flow, or due to the ingestion of a toxin (such as antifreeze or rat poison) or eating poisonous foods such as raisins or grapes.
Chronic Kidney Disease (CKD)
CKD is a slowly progressing illness, where the kidneys gradually lose function. Although there isn’t a cure, the disease may be managed and slowed with the correct care.
There a 4 progressive stages to CKD (4)
| Stage I – Damage begins to occur, but elevated waste products are not yet identifiable in the blood. Typically, no symptoms present. |
| Stage II – Waste filtration continues to decline, elevated waste products in blood and urine. Typically, no physical symptoms present. |
| Stage III – Waste filtration continues to decline, further elevating waste products in blood and urine. Symptoms begin to present as excessive thirst and urination. |
| Stage IV – Severe decline in kidney filtration, causing toxins to build up in the blood. Myriad of physical symptoms, including weight loss, vomiting, diarrhoea and lethargy. |
Most dogs do not present with physical symptoms until around 70-75% of renal function is lost and they are at stage III or IV (2).
Dietary Management of CKD
Many vets will recommend a ‘prescription’ kidney diet for dogs with CKD, which has altered protein, phosphorous and sodium levels. However, the condition can also be successfully managed with a raw diet, albeit with some certain criteria being met. Some of they key nutrients to consider are Protein, Phosphorous, Moisture, and Fats.
Protein
Dogs would naturally choose to obtain their calories from protein and fat, with some complex carbohydrate content to provide additional benefits. Protein quality is defined by the amino acid composition of the protein source, as well as its digestibility and bioavailability, which is typically higher in animal sources as opposed to plant materials. It is important to feed dogs with CKD highly digestible, quality animal protein.
The efficacy of protein restriction divides opinion. Whilst protein moderation has been shown to improve symptoms in uraemic dogs, restriction of protein has not been shown to slow disease progression (1). Protein itself does not contribute to kidney damage, it’s the waste products of it’s digestion which can cause the issue. Thus, protein restriction is initially suggested, to reduce nitrogenous waste (5). In late-stage CKD, nitrogenous waste can build up in the blood, at which point restriction may be necessary. In advanced stages of CKD proteinuria may occur, as damage to the glomerulus causes leakage of protein into the urine, and as the number of functioning nephrons decreases, this will worsen. Whilst protein may need to be moderately reduced to control proteinuria, a very low protein diet is not recommended.
Protein quality will also have an impact, which affects their digestibility, and subsequent waste products (this is important as the kidney is responsible for removing these). The higher the protein quality, the less nitrogenous waste is left behind when digested (eggs and raw meat are the highest quality protein for dogs). Thus, a dog with kidney issues can eat a larger quantity of high-quality protein compared to low-quality protein, without as much waste being left behind. Raw animal protein is most suitable, as less nitrogenous waste is produced than when protein is processed and more challenging to digest (6).
Phosphorous
Dietary phosphorus is an essential nutrient, being a component in DNA, RNA, cell membranes and ATP, making it the spark for life (7,8). Phosphorus content in the body is maintained by intestinal absorption, and excretion via the kidneys. When kidney function is impaired, phosphorous can accumulate in the blood. Thus, in the case of CKD, a lower phosphorus diet is recommended to ease stress on the kidneys. Phosphate binders, such as calcium carbonate, may be used to further reduce phosphorous uptake, by binding the phosphorous in the food, allowing more flexibility when feeding (1). We suggest consulting your vet to discuss your dog’s options.
It is also important to note that not all phosphorus is equal. Inorganic phosphorous proves a greater risk than organic phosphorous for absorption issues. Organic phosphorous is typically water soluble, and present in raw animal and plant ingredients in the diet. Whereas inorganic phosphorous is often added during processing, to meet nutritional requirements (7). In fact, dietary phosphorous from natural food ingredients, such as meat and vegetables, does not appear to affect post-prandial plasma phosphorous levels as drastically (9).
Some low phosphorus meats include: Green tripe, Chicken, Duck, Rabbit
Some medium phosphorous meats include: Beef, Lamb, Turkey
The highest phosphorous foods are considered to be bones, dairy and organ meat (particularly liver), however this does not mean these foods need to be avoided, they should just be fed in moderation. The best way to reduce phosphorous is feeding fattier meats, containing moderate amounts of quality protein, and low phosphorous carbohydrates. Remember to increase fat levels gradually to prevent tummy upsets. In dogs prone to pancreatitis, fat may need to be reduced, and the content of low phosphorus vegetables increased.
Moisture
Ensuring adequate hydration is important in all animals but is particularly important for those with kidney disease. Feeding a dry food with inherently low moisture content (<10%), will exert chronic stress on the kidneys if the daily water quota is not met, increasing the risk of kidney disease and stones (10). A raw diet contains >60% moisture, allowing dogs to receive hydration through their meals.
Fats
Inflammation is a primary factor contributing to the development of kidney disease. The excess carbohydrates and cooked fats in dry foods can elevate Omega 6 levels, and subsequently impact the Omega 6:3 ratio, becoming pro-inflammatory (3). Omega 3 fatty acid supplementation is suggested, specifically DHA and EPA due to their anti-inflammatory properties and renoprotective effects (5). In experimental studies, supplementation of DHA and EPA reduced proteinuria in dogs suffering from CKD (11). Occasional oily fish, salmon oil, and flaxseed provide dogs with a good source of additional omega 3 fatty acids.
So, What Criteria Should My Raw Diet Meet?
In the early stages of CKD, fresh raw meat, greens and herbs is the best diet you can offer, but as the disease progresses you may need to tweak the diet, by dropping the phosphorous content and supplementing additional omega-3, eventually, protein may need to be dropped in end stage CKD.
Palatability is another key aspect of the diet, especially in elderly pets, as circulating toxins and reduced olfactory senses can cause a disinterest in food (1). Raw food contains fresh fats, making it naturally palatable. Additionally, fresh raw kidney is packed with nutrients that the kidneys need. It packs a punch nutritionally, so only feed as 3-5% of the diet, to ensure you do not feed too much phosphorous.
Pets with advanced stage CKD should have high quality protein, in a lower quantity. A moderately restricted yet high quality protein diet is suggested to reduce the work on the kidney and nitrogenous waste products which can exasperate symptoms (1). It may also be beneficial to add more water-soluble vitamins into their meals (mashed fruit and vegetables), as these are often lost due to excessive urination.
References
- Collins, S. (2016) ‘The role of nutritional management of cats and dogs with renal disease,’ Veterinary Nursing Journal, 31(8), 237-240. Available at: http://dx.doi.org/10.1080/17415349.2016.1194634
- Brown, S. A. (2013) ‘Renal Dysfunction in Small Animals,’ MSD Veterinary Manual. Available at: https://www.msdvetmanual.com/urinary-system/noninfectious-diseases-of-the-urinary-system-in-small-animals/renal-dysfunction-in-small-animals
- Olson, L. (2010) Raw & Natural Nutrition For Dogs
- Brown, S. A. (2018) ‘Noninfectious Diseases of the Urinary System in Dogs,’ MSD Veterinary Manual. https://www.msdvetmanual.com/dog-owners/kidney-and-urinary-tract-disorders-of-dogs/noninfectious-diseases-of-the-urinary-system-in-dogs
- Cline, M. G. (2016) ‘Nutritional Management of Chronic Kidney Disease in Cats and Dogs,’ Today’s Veterinary Practice.’ Available at: https://todaysveterinarypractice.com/nutrition/acvn-nutrition-notesnutritional-management-of-chronic-kidney-disease-in-cats-dogs/
- Kerr, K. R. et al. (2012) ‘Apparent total tract energy and macronutrient digestibility and fecal fermentative end-product concentrations of domestic cats fed extruded, raw beef-based, and cooked beef-based diets, Journal of Animal Science, 90(2), 515-522. Available at: https://doi.org/10.2527/jas.2010-3266
- Stockman, J. (2024) ‘Dietary Phosphorus and Renal Disease in Cats,’ Journal of Feline Medicine in Surgery, 26, 1-6. Available at: https://doi.org/10.1177/1098612×241283355
- Patton, R. (2011) Ruined by excess, perfected by lack: the paradox of pet nutrition.
- Coltherd, J. C. et al. (2018) ‘Not all forms of dietary phosphorous are equal: an evaluation of postprandial phosphorous concentrations in the plasma of the cat,’ British Journal of Nutrition, 121, 270-284. Available at: https://doi.org/10.1017/s0007114518003379
- Billinghurst, I. (2001) The BARF Diet
- Parker, V. J. (2021) ‘Nutritional Management for Dogs and Cats with Chronic Kidney Disease,’ Veterinary Clinics of North America: Small Animal Practice, 51, 685-710. Available at: https://doi.org/10.1016/j.cvsm.2021.01.007
Lucy James, BSc (Hons) Bioveterinary Science
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