ABSTRACT: It is widely accepted that nutrition plays an important role in supporting cats and dogs with renal disease, and it is proven to increase longevity when a specifically formulated renal diet is fed. Adapted levels of nutrients such as phosphorus, protein and calcium are important to assess when selecting an appropriate diet, and the hydration status of the patient and how to keep on top of water intake must be considered alongside this. Not only is the choice of diet important, but also the palatability as well as when and how the diet is introduced and fed.


Veterinary Nurses are often involved in the diagnosis, treatment and management of cats and dogs with renal disease, so it is important to understand not only the disease process itself, but also the treatment and management options. This article focusses on the importance of nutrition for cats and dogs with renal disease, and how adaptations to both the diet and how it is administered can contribute to successful management.


The two most common renal conditions which affect cats and dogs are Acute Renal Failure (ARF) and Chronic Renal Failure (CRF).

In ARF there is a sudden and rapid deterioration of the ability of the kidneys to regulate water balance. Causes include ischaemia, nephrotoxic injury and post-renal causes such as urinary obstruction or rupture, and may be reversible or irreversible (Allen, Polzi, & Adams, 2000). Clinical signs include sudden onset anorexia, vomiting, diarrhoea and oliguria/ anuria.

In CRF, there is a progressive and irreversible loss of kidney function, with functional nephrons being replaced by non-functional scar tissue. CRF may be congenital/familial or secondary to acquired disease, insult or injury (Elliott & Lefebvre, 2006). Clinical signs include polydipsia/polyuria, vomiting and anorexia. Diseased kidneys have a mixture of functional and non-functioning nephrons, with renal function being influenced by the number of functional nephrons remaining (Elliott & Lefebvre, 2006). Loss of functional nephrons leads to a decreased glomerular filtration rate, which in turn reduces the ability of the kidneys to filter and excrete waste products efficiently. Accumulation of nitrogenous waste products such as urea, creatinine and ammonia leads to azotaemia and uraemia, which can affect the gastrointestinal tract, cardiopulmonary, metabolic and endocrine systems as well as fluid, electrolyte and acid-base balance (Elliott & Lefebvre, 2006). Reduced renal function also affects the production of calcit- riol and the kidneys’ ability to degrade parathyroid hormone, and the resulting changes to calcium and phosphorus metabolism may lead to hyperphosphatemia, osteodystrophy and deposition of calcium in soft tissues (Case, Daristotle, Hayek, & Raasch, 2011).

Nutritional considerations

The aim when managing cats and dogs with renal disease is to stabilise the patient, alleviate clinical signs and limit further deterioration. When presented with an animal with renal disease, the priority is to administer any necessary emergency treatments and rectify any fluid and electrolyte imbalances (Figure 1). Once the patient is stable, medical treatments and nutrition can be instigated. Any complicating factors will need to be resolved, for example by treating concurrent conditions such as urinary tract infections.

Nutrition is an important factor to consider in renal disease, with several studies showing that patients fed a “renal” diet live longer than those who remain on a “standard” diet (Bartges, 2012; Elliott, Rawlings, Markwell, & Barber, 2000; Plantinga, Everts, Kastelein, & Beynen, 2005).

Figure 1. Fluid and electrolyte imbalances should be addressed before commencing nutrition


Water is often not mentioned when discussing nutrition as animals are provided with this separately to the diet. However, hydration is particularly important in patients with renal disease as they have reduced urine concentrating ability, and combined with reduced water intake due to inappetance, this makes them more susceptible to dehydration. Patients with renal disease should be encouraged to take in more water, either by encouraging spontaneous water intake, or including it in the diet. Methods include water fountains or slow dripping taps for cats, or adding water to the diet, whether that is wet or dry.

Although there are currently no studies which confirm the benefits of maintaining hydration in patients with CRF, the ISFM consider this to be a crucial part of management (Sparkes et al., 2016). They believe that as well as maintaining hydration (which may support renal blood flow); fluid therapy may also be beneficial in addressing electrolyte and acid-base disturbances and diluting uraemic toxins. Patients which are presented with unstable CRF may therefore require hospitalisation for intravenous fluid therapy to achieve a good hydration status as well as helping to correct any electrolyte and/or acid-base disturbances.

In patients which are being tube fed, the nature of the diet will in itself be high in moisture content, so as long as the patient’s electrolyte and acid-base balance is stable, it is possible to provide daily water requirements via enteral tube feeding alone, removing the need for intravenous fluid therapy. Sparkes et al. (2016) comment that administering water via a feeding tube may be preferable to subcutaneous fluids in many cases.

Wet or dry food?

In terms of nutrient profile, there is little difference between wet and dry renal diets. Wet diets have the added benefit of a higher water content (±80% versus ±8% in dry diets), which, if the patient is eating well, means that their dietary water intake will be increased. Wet diets do have a lower energy content gram for gram compared with dry diets, as this extra water content dilutes the calories, meaning that the patient has to eat more volume to meet its nutritional needs compared to dry. The main factor will be patient (and possibly owner) preference. As long as the patient consumes the recommended amount of food and has a good water intake, then there is no particular preference of one over the other.

Tube feeding

Often overlooked as a long-term solution for the nutritional, hydration and medical management of patients with chronic kidney disease, enteral feeding tubes (particularly oesophagostomy) can play an important role in increasing owner and patient compliance and minimise hospitalisation (Ross, 2016). With liquid renal diets now available for cats and dogs, placing a long-term feeding tube is a proactive way to provide appropriate nutrition as well as to ensure adequate water intake and may allow easy administration of medications.

In hospitalised patients, nutrition is an important part of patient management and should be addressed early on. If a patient has been anorexic for more than three days (including days before it was admitted), or has not eaten at least 80% of its resting energy requirement per day for the last three days, then assisted feeding must be implemented. Naso-oesophageal tubes are easy to place, do not require general anaesthesia, and can be left in situ for up to a week (Figure 2). A liquid diet should be used when feeding via a naso-oesophageal tube, with a specially formulated diet for patients with renal disease the diet of choice.

Figure 2. Naso-oesophageal tube

Key nutritional adaptations

Phosphorus – hyperphosphataemia can be managed by limiting dietary phosphorus intake to help normalise serum phosphorus levels and help prevent secondary hyperparathyroidism (Elliott & Lefebvre, 2006) . A study of cats with naturally occurring renal failure by Elliott et al. (2000) concluded that severe restriction of phosphorus can double life expectancy after diagnosis of CRF. Current consensus is that restriction of phosphorus is a key factor in slowing the progression of renal disease.

Protein – in patients with renal disease, damage to the glomeruli, tubules and/ or interstitium causes protein to be lost via the urine, resulting in proteinuria and hypoproteinaemia. Azotaemia and uraemia occur due to accumulation of metabolites derived from dietary protein, with high levels exacerbating azotaemia (Elliott & Lefebvre, 2006).

It is important to provide enough protein so that the animal does not suffer from protein deficiency. Protein also enhances palatability, as well as providing energy. For patients with renal disease, a moderately restricted yet high-quality protein is recommended to help limit the amount of nitrogenous waste products produced and therefore the workload on the kidneys.

Fat – fat increases the energy density of the diet, allowing the patient to obtain its nutritional requirements from a smaller volume of food, which minimises gastric distention, thereby reducing the risk of nausea and vomiting (Elliott & Elliott, 2008). Providing energy in this form also spares protein from being used for energy. Fat also improves palatability, which is another important factor in managing patients with renal disease whose appetite may be affected by the underlying disease processes.

Introducing a renal diet

It is important to remember to never start a patient on a renal diet in a hospital situation. Although it is tempting to get the patient eating the diet before it goes home to help with owner compliance, it is actually more likely that once the patient gets home it will no longer eat the food. This is because the animal may associate the food with either nausea and/or depression experienced during this time, or the stress of being in the hospital environment (or both).

Ideally, a highly palatable, highly digestible diet (such as a gastrointestinal diet) should be fed during hospitalisation (Figure 3). However, it is better that the patient eats something than nothing at all, so in the inappetant patient it is a case of trying different foods little and often.

Figure 3. A highly palatable, highly digestible diet should be fed during hospitalisation

On discharge, the owner should be fully informed of the benefits of a renal diet and be given a selection of wet and dry products to take home and try. It is also important to educate the owner that the animal is likely to “go off” its food at some point for no particular reason. This is because the renal disease process affects the animal’s sense of taste and smell, and they may suddenly refuse a diet they have been happily eating for several weeks or months. Encourage the owner to keep a selection of different variants of the diet at home in case this should occur, remembering that because an animal refused a particular variant in the past it does not necessarily mean that it will refuse it again. As with any dietary change, the new diet should be introduced over a 7-10-day period by slowly mixing it in with the current diet. Sparkes et al. (2016) recommend that medications should be administered via an alternative food to avoid food aversion.

As mentioned previously, consider the use of a long-term feeding tube, particularly in chronic patients. If long-term tube feeding is indicated, then also consider if this option is suitable for the pet owner – do they have the time/ability to carry this out? If the pet owner is committed to tube feeding then take time to show them how to care for the tube and actively get them to participate in feeding sessions while their pet is in the hospital and you are on hand to assist until they are confident to carry the procedure out alone at home.


Sarah Collins Dip Avn (Medical), RvnVts (Ecc), Cert San Cert Cfvhnut

Sarah qualified as a veterinary nurse in 1995. Following 11 years in first opinion/ referral practice, Sarah moved to the University of Bristol to work in the intensive care unit. During her seven years in this role, Sarah obtained both the Diploma in Advanced Veterinary Nursing (Medical) and the Veterinary Technician Specialist in Emergency and Critical Care qualifications. Sarah now works for ROYAL CANIN® as a Veterinary Marketing Executive.

Email: Sarah.collins@effem.com


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Sparkes, H. A., Caney, S., Chalhoub, S., Elliott, J., Finch, N., Gajanayake, I Quimby, J. (2016). ISFM consensus guidelines on the diagnosis and management of feline chronic kidney disease. Journal of Feline Medicine and Surgery, 18, 219-233.

Veterinary Nursing Journal •
VOL 32 • September 2017