NUTRITION is a cornerstone in the management of many diseases and its importance in veterinary medicine is increasingly recognised.
Recent years have seen changes in nutritional recommendations for the management of certain diseases and new discoveries have widened the vet’s armoury.
Heart disease
Heart disease is a common reason for a visit to the veterinary practice, but this area is often neglected in nutritional terms.
Cardiac cachexia can be an important factor in the decision-making process for euthanasia for pets suffering from heart failure, and so should be addressed. Diet can provide much needed energy and helps to correct some of the electrolyte imbalances commonly encountered and sometimes exacerbated by drug therapy.
Much controversy has existed over the years regarding salt restriction in canine cardiac failure: when is it best to start salt restriction, and to what level? Because of the effects on sodium balance of diuretics and ACE inhibitors, judging an optimal level is difficult.
Restricting too much too soon can lead to early activation of the reninangiotensin-aldosterone system, and this is thought to be undesirable. Therefore, moderate restriction during early stages of heart failure and avoidance of high salt is thought appropriate, whilst in later stages, more severe restriction is advocated.
Recent studies show an interesting and potentially beneficial application for the use of omega-3 fatty acids. Fish oil supplementation can decrease interleukin concentrations and lead to a positive effect on appetite.
Furthermore, in a group of arrhythmic boxers with cardiomyopathy, supplementation with omega-3 fatty acids helped to stabilise myocardial transmembrane potentials and decreased frequency of arrhythmias, potentially lessening the risk of sudden death.
Renal disease
Nutritional management remains essential. It is the only intervention (other than using ACE inhibitors in proteinuric CKD cats) that shows a decrease in mortality and increased survival time.
In cats, the benefits of feeding a renal failure diet in early stages (IRIS Stages I and II) are less clear (though potentially beneficial), while intervention for later stages is proven.
An appropriate diet can help deal with many of the metabolic and biochemical derangements seen and help to ameliorate clinical signs. Though previously renal failure diets were associated with palatability issues, great efforts on the part of nutrition companies have helped to increase acceptance.
The detrimental effects of catabolising body protein in any patient refusing to eat can be serious. Therefore early feeding is essential and it is recommended to start with the pet’s favourite food during the initial hospital stay and transition to a renal diet when treatment has allowed a return to the home environment.
In both dogs and cats, phosphorus restriction is key, helping to decrease the toxic levels of PTH and the effects of secondary renal hyperparathyroidism. The benefits of restricting protein on renal function are less clear, although the reduction of nitrogenous waste products and hence improvement in clinical signs is a goal.
In rats and humans there is evidence that protein restriction slows the disease process; there is some evidence for a potential benefit of this kind in cats, but no evidence as yet in dogs. (There are, however, clear benefits in restriction for proteinuric dogs at any stage.)
In cats, restriction has been shown to decrease glomerular hyperfiltration, proteinuria and histological glomerular damage compared to cats on a high protein diet.
Increased calories from fats help to lend palatability to renal diets and are of benefit in combating weight loss. Specific benefits of fatty acids come mainly through their effects on renal blood flow – through prostaglandin and thromboxane mediated effects on systemic hypertension helping to improve renal haemodynamics. There is also evidence that fatty acids may decrease cholesterolaemia and help with preservation of renal function in experimental models.
Extensive studies of the risks v. benefits of salt restriction haven’t been carried out, but work done by Claudia Kirk showed that a higher salt load in cats with sub-clinical kidney disease led to a progression to overt renal failure.
Some salt restriction is helpful in combating hypertension, but too severe salt restriction will adversely affect palatability, and may also promote excess potassium renal excretion.
Inflammatory bowel disease
Food allergy (FA) should be investigated in every case of IBD, as the diagnosis of this condition is one of exclusion. Most dogs with FA will react to only a few allergens.
Serological tests do not have a good positive predictive value – some animals may show positive IgE levels to certain foods, but it isn’t known if this is clinically relevant.
In truth, an elimination food trial is the only reliable way of identifying food allergy. An ideal diet is one with a single source, novel protein, restricted in amount, low in fat, highly digestible and lactose and gluten free.
Three choices are available here: home-cooked, novel protein and hydrolysed diets. In the latter the protein (usually chicken or soy) has been enzymatically cleaved to yield small less-allergenic peptides.
Recommendations for home-made diets include proteins such as venison, rabbit, salmon, horse or kangaroo, with carbohydrate from rice, potato, sweet potato, tofu or yam. Home-made diets, however, may not be practical in every case and compliance can be improved by feeding a commercial diet.
There has also been concern voiced over cross reactivity between some meats, and therefore doubt re the reliability of any result. This is currently under investigation and it may be that to achieve a truly hypoallergenic diet, a hydrolysed diet is necessary.
Liver disease
Acute liver disease requires little and often feeding of a high quality diet and there is some evidence that dairy or soy protein may be best. Protein restriction is logical to help decrease liver workload but too severe restriction will inhibit hepatocyte regeneration.
In chronic liver disease which is often idiopathic, a high quality protein is needed, supplemented with zinc, B vitamins and antioxidants. Little and often feeding is again needed. Serum albumin should be monitored and protein intake adjusted.
Pancreatic disease
The traditional recommendation of nilby-mouth in the treatment of pancreatitis has been recently challenged. In vomiting cases this is still sensible, but “rest” is now thought to play little role in resolution.
Recent reports show that enteral and parenteral nutrition are both well tolerated, and there is no evidence that enteral nutritional aggravates the condition.
Rather, some patients do better with early enteral feeding and this has the added benefit of feeding the intestinal wall directly to help maintain the gut immune barrier.
Therefore, it is now considered acceptable practice to offer small amounts of food and water periodically, increasing the quantity if well tolerated (unless vomiting persists, in which case withhold food and water and reintroduce 24-48 hours after vomiting stops).
For animals which are not eating, a naso-oesophageal (NO) or oesophagostomy (O) tube can be placed (avoid naso-gastric as this can cause reflux and consequent oesophagitis). A jejunostomy (J) tube is gold-standard as it introduces food below the level of the pancreas, but the need for surgical placement makes it less suitable.
The diet fed should be highly digestible. High fat foods should be avoided and in patients with repeated episodes of pancreatitis it is advised to feed a diet moderately restricted in fat. Obese dogs and breeds susceptible to pancreatitis, such as the miniature schnauzer (through a tendency for hypertriglyceridaemia) should be fed a diet more restricted in fat.
In some studies, feeding a low fat diet in association with pancreatic extracts and MCTs led to less exocrine pancreatic stimulation.
In cats though, there is little evidence that fat content is important and a highly digestible bland diet is advocated. NBM in non-vomiting patients is also no longer recommended, as cats can often develop hepatic lipidosis in association with pancreatitis. Therefore if they are not voluntarily eating, a feeding tube or total parenteral nutrition may need to be started.
Parenteral nutrition is difficult to implement in practice as it requires a central line in most cases and careful monitoring of sepsis. Therefore, in practice situations, an NO or gastrostomy tube may be used in non-vomiting cases.
Exocrine pancreatic insufficiency (EPI)
The dietary recommendation here is for a highly digestible diet used in combination with a commercially prepared dried pancreatic extract. These are available in tablets, capsules, powders and granules, but there is some evidence that powder may work better.
In one recent study, though, the use of powder was associated with oral bleeding in some dogs; this side-effect can be managed by moistening the food and powder. Even with treatment, however, digestion never returns to normal and patients may always eat more to maintain their body weight.
A highly digestible, low fibre food can help to decrease borborygmi and flatulence and help decrease faecal volume. If more weight gain is needed, medium-chain triglycerides (MCTs) can be supplemented although palatability can be an issue with these.
The diet should not be greatly restricted in fat as this can further decrease fat assimilation and lead to deficiencies of fat-soluble vitamins and essential fatty acids.
Osteoarthritis (OA)
Conventional aims in the management of OA are to keep both the joint and the patient moving and current interventions are aimed at controlling inflammation and protecting the cartilage from degenerative processes.
There have been many nutritional advances in this area in recent years. The use of the omega-3 fatty acid eicosapentaenoic acid (EPA) in diets for OA has clear clinical evidence for decreasing inflammation in the joint by encouraging the production of less inflammatory eicosanoids. As a result, NSAID dosage can be decreased in some patients.
Chondroprotective benefits from nutraceuticals such as glucosamine and chondroitin carry less clear clinical evidence, but many vets and owners report improvements.
Green lipped mussel is thought to have an anti-inflammatory effect and also contains glycosaminoglycans. Its mechanism of action is unknown, though there is evidence of an improvement in joint swelling and lameness after eight weeks of feeding.
An often ignored benefit to OA patients is that derived from optimising body weight. A loss of even 8-10% bodyweight in overweight patients can result in a significant improvement in mobility.
Atopy
It is now thought that some atopic dogs (and humans) have an abnormal fatty acid metabolism. In several studies of atopic pruritic dogs, supplementation with fish oil (a source of EPA and DHA, docosahexaenoic acid), and/ or borage oil or evening primrose oil, helped to decrease inflammatory reactions in the skin and itching.
The ratio of omega-6:omega-3 fatty acids used may be more important than the absolute amount and ratios of between 7:1 and 5:1 have been suggested.
Many dogs suffer from adverse reactions to food as well as atopy, and one study showed that feeding a novel protein diet with increased levels of EPA and LA (linoleic acid) and a ratio of omega-6 to omega-3 of 6:1 resulted in improvement in both owner and vet assessment of clinical signs.
Diabetes mellitus
The key to nutrition and feeding in the management of canine and feline diabetes is consistency. The food type should be controlled and the amount of calories consumed kept the same day to day.
Home-made diets may prove troublesome in this respect and so commercial diets are preferable. Palatability of the diet is particularly important in pets on shorter acting insulins, as the entire food portion needs to be eaten within a short space of time. In some cases, therefore, it may be preferable to try to stabilise the patient on standardised portions of their regular food, rather than to start to change the diet at this stage.
For all diabetic patients body weight should be optimised. Many diabetic cats when initially diagnosed may be overweight and reducing their weight helps to decrease insulin resistance and improve sensitivity.
Underweight diabetics should be fed a low fibre highly digestible diet to bring them up to ideal body weight. For normal or overweight dogs, diets high in insoluble fibre may help to decrease post-prandial glucose fluctuations. A high fat diet should be avoided as fat can contribute to impaired insulin secretion and efficacy.
In cats, recent studies have shown a better response in diabetic control from feeding a high protein-low carbohydrate diet. This can be particularly beneficial when fed to overweight cats at a reduced level to decrease calorific intake and helps to decrease insulin resistance. Studies also showed that the dosage of insulin in some cats was able to be reduced whilst on this type of food.
FLUTD
Multimodal environmental modification (MEMO) may help reduce the recurrence of clinical signs of cats with lower urinary tract disease. A dietary assessment should take place in every case and where uroliths are implicated, diets restricted in the building blocks of that particular urolith should be used. Increasing water intake is of vital importance; this lowers the specific gravity of the urine and encourages frequent voiding, while decreasing noxious components of urine with potential to irritate.
A canned diet is the easiest way to do this – in one study lower urinary tract signs recurred in only 11% of affected cats within a year which were fed a canned food, compared to 39% of cats fed the dry food of the same formulation.
It should be remembered that cats like to eat and drink in separate locations and the water bowl should be made of glass, ceramic or metal with a wide brim. The water level should be kept to the very top of the bowl. Water fountains are very useful and making a “soup” from the canned preparation can increase water intake further.
Obesity
The common wisdom of decreasing the calorific intake to between 60 and 70% of that needed to maintain normal body weight, in order to lose weight, is still appropriate. Decreasing the amount of regular food fed, however, is not recommended as this decreases intake of other nutrients at the same time.
A commercial diet for weight loss (not a “light” diet – this will not be restricted enough in calories) should be used. A rate of loss of 1-2% per week is ideal, but 0.5-1% per week may be more realistic in many cases.
High levels of insoluble fibre in the diet will create gut distension and help give satiety through stretch receptor feedback. It also leads to less food being consumed and decreases transit time through the small intestine (therefore allowing less time for absorption).
A combination of soluble and insoluble fibre, however, can lead to less of a problem with larger stool size and still retain satiety benefits. The use of increased levels of protein can also lend benefits.
Gram for gram protein produces a greater postprandial thermogenic effect, with the result that fewer calories are subsequently available as excess to be laid down as fat. Additionally, high protein diets help preserve lean body mass during weight loss and have a positive effect on satiety through cholecystokinin secretion.
For cats, a high protein-low carbohydrate approach to weight loss exploits their unique metabolism and encourages burning of fat to provide energy when fed at an appropriate calorific intake.
Canine cognitive dysfunction
The canine brain has been shown to age in a similar way to humans and similarities exist histopathologically between Alzheimer’s in people and dogs with severe cognitive dysfunction.
Whilst it is not possible to reverse these histopathological changes, an improvement in the clinical behavioural signs in dogs with cognitive dysfunction can be brought about through nutrition.
Studies have shown a benefit from feeding an antioxidant-enriched diet, supplemented with omega-3 fatty acids, which is thought to work by increasing the efficiency of oxidative processes to help prevent neuron death and through helping diseased but still functioning neurons to work better.
And finally on rabbits…
Conditions such as gastric stasis and non-obstructive ileus will benefit from fluid therapy. Commercial high fibre herbivore recovery diets are now available to encourage feeding in anorexic animals and these can be syringe fed. Vegetable baby foods, slurries of ground rabbit pellets and hay can be also used.
Hitherto the use of enzymes such as papain have been popular to help digest trichobezoars, but the use of bromelin in pineapples is controversial, with potential problems identified such as clostridial overgrowth.
■ References are available on request.
