Background

The trend of feeding raw foods to dogs and cats was apparently started in the early 1990’s by an Australian veterinarian who wrote a book promoting the virtues of feeding raw food to dogs 1, and the abbreviation “BARF” (usually taken to mean either “Biologically Appropriate Raw Food” or “Bones and Raw Food”) is now a widely used acronym in this context. There are several other concepts and philosophies for “correct raw feeding”, such as the “Prey Model” or the “Ultimate Diet” 2, but these are much less well known, and the BARF acronym is now generally accepted as a synonym for feeding raw foodstuffs.

BARF rations are oriented towards adapting the predator-prey system for domestic dogs and cats, giving them food consisting essentially of raw meat, with a high proportion of “meaty bones” and organs (Figure 1). On top of this fruit and vegetables, nuts, oils and herbs are also fed, with eggs and dairy products in lesser amounts. The feeding of grain products is generally not recommended, although other carbohydrates such as potatoes or pulses are sometimes allowed. Despite the fact that “artificial ingredients” (such as mineral or vitamin preparations) are proscribed, there is already a large selection of products on the market specially aimed at supplementing BARF rations.

The most important motive for an owner in choosing a BARF diet for their pet is the desire for a “more natural, healthier food” (Figure 2) 3 4. Other reasons include a chronic illness (such as skin disease, gastrointestinal disorders and allergies) which the owner hopes will improve on the new diet, and various claims that commercial ready-to-serve foods contain only “waste materials and chemical ingredients” and are responsible for various diseases. These stories make many pet owners feel insecure and cause them to search for “healthier” alternatives.

The information sources for BARF are primarily internet sites and books (Figure 3) 3 4. Unfortunately, these sources are normally written by lay people and contain misleading or even inaccurate information, although they may be presented in a very scientific style. BARF is frequently propagated in a very emotional manner and portrayed as a cure-all for diseases, problems and behavioral abnormalities. This can result in some owners, who would not normally consider feeding their pet raw food, being convinced that they will injure their pet by feeding them commercial diets.

Claims and facts

It must be said firstly that no scientific studies exist on the long-term effects of raw diets. Discussions on the advantages and drawbacks can therefore only be conducted on the basis of inferences from knowledge of food science and nutritional physiology. Various advantages are often cited for feeding BARF compared to ready-to-eat diets, and these are listed below, with comments as appropriate.

• Knowing the origin and composition of the food
  - poorly tolerated or unpopular foods and allergens can be easily avoided.
  
  

• Avoidance of additives
  ­- pet owners often view additives as having a bad reputation and to be “unnecessary chemicals”. The use of flavorings in commercial diets is frequently overestimated by owners, and many believe that some manufacturers add so-called “attractants” to their foods which supposedly fool the animal into accepting lower-quality nutrition and even make it “addicted” to the food. Many pet owners are unaware that essential vitamins and trace elements fall under the “additives” term and that all additives must go through the relevant country’s regulatory approval procedures.
  
  

• Avoidance of grain products
  ­- the idea that gluten and cereals in general are damaging to dogs and cats is another popular rumor with no scientific basis. One can assume that many domestic dogs received lots of grain-based products (e.g., bread, dog biscuits) before the introduction of commercial dry diets. Current research suggests that dogs have genetically adapted to carbohydrate foods throughout their evolution 5. Cats can also metabolize carbohydrates, albeit in lower amounts than dogs. Gluten-containing products must only be avoided if the animal has gluten intolerance, but this is rare.
  
  

• The effect of heat destroys nutrients
  ­- it is undoubtedly true that some nutrients, especially the B vitamins and vitamin A, are not heat-stable, but this is easily managed through the addition of nutrients in sufficient quantity to compensate for heat treatment during the manufacturing process. In addition, the availability of some amino acids, especially lysine, is reduced by heat treatment, but in practice a lack of essential amino acids is not usually an issue for dogs and cats as long as they are fed a diet containing good quality animal protein.
  ­- The destruction of enzymes in meat by heating is also cited as an argument for raw feeding, claiming that feeding with heat-treated meat leads to an “enzyme deficiency”. It may be that owners mistakenly equate this with the idea that enzymes within the food are necessary for the digestion process.
  
  

• Lower stool quantity, better stool consistency
  ­- BARF diets are normally highly digestible, and certainly more digestible than low-quality commercial feeds. However, household cooking does not negatively influence the digestibility of meat, and highly digestible homemade diets can be constructed from cooked ingredients.
  
  

• Improved dental health due to increased chewing
  ­- chewing tough pieces of meat and gnawing on bones strengthen the periodontium and clean the tooth surface. This seems plausible, although it must be pointed out that injuries can occur from eating bones (Figure 4).
  
  
  

Most of the frequently-cited positive effects, such as “shiny coat”, “lively behavior” and “better constitution”are subjective impressions and are difficult to prove objectively in a clinical setting. Whilst there is no doubt that nutritional deficiencies or feeding a specific diet that is unsuitable for an individual animal can cause issues such as poor appetite, digestive disturbances and skin problems, many diseases can also result in such signs. It seems that pet owners are currently very sensitive to the idea of “food intolerance from commercial diets”and if their pet is unwell they may quickly switch to a raw diet without considering other, more plausible causes such as parasites or infection.

Risks of raw feeding

The following risks must be considered with feeding raw diets:
1. Nutritional imbalances
2. Hygiene risk from raw meat
3. Problems caused by eating bones
4. Unsuitable and harmful ingredients

1. Nutritional imbalances

It is frequently asserted that a “food close to nature” will automatically cover all nutritional needs and that “artificial” supplementation is unnecessary and could even be harmful. Certainly, whatever diet is fed, the body can only absorb nutrients that are actually contained within the food. Knowing about the nutritional content of ingredients and how they can be combined in sensible proportions is necessary in order to create a ration that covers the body’s needs. There are numerous books and websites that offer complete BARF recipes, but unfortunately the majority of these are incorrect in various aspects. The following errors are frequently encountered in such recipes:

• Very high protein content
  ­ - currently thought to be harmless for healthy dogs, but diets high in protein are not recommended for older animals especially those suffering from liver or kidney disease.
  

• Low protein content

• Very high fat content (> 30% in dry matter)
  ­ - increased risk of pancreatitis in dogs 6.
  

• Calcium over- or under-supplementation and incorrect calcium-phosphorus ratio
  ­ - especially dangerous for growing pups (Figure 5).
  

• Vitamin A deficiency or over-supplementation
  ­ - cats cannot convert carotenoids into vitamin A and must eat animal products that contain vitamin A.
  

• Vitamin E deficiency
  

• Vitamin D deficiency
  ­ - it is sometimes asserted that dogs and cats do not need vitamin D supplementation because it can be produced endogenously – this is erroneous!
  

• Deficiency in trace elements (zinc, copper, iodine, manganese)
  

• Use of unnecessary or harmful supplements
  

For more on these nutritional deficiencies, the clinician is directed to the plethora of scientific literature on basic nutrition and physiology. It must be stressed that an animal with specific deficiencies in vitamins and trace elements can be free of clinical signs for months or even years until the body has exhausted its reserves or until an increased need arises due to illness. Because an animal can appear to be well, a pet owner will frequently argue “my dog/cat seems healthy, so there cannot be a nutrient deficiency” or “the blood tests were normal, therefore what I feed my animal must be right”.

It is worth pointing out to an owner that an optimal nutrient supply cannot be determined through such tests; blood values give a momentary picture, while long-term changes do not appear until massive deficiencies or over-supplementation accumulate. In the case of calcium and phosphorus, blood levels are constantly held within a tight range – changes indicate a pathological process that seldom has anything to do with food. In order to evaluate what an animal is receiving in terms of nutrient supply, its diet must always be assessed!

Conventionally, the nutritional requirements of animals are calculated using figures based on the recommendations of the research council or the regulatory bodies* 7.

* Depending on the country of manufacture and/or sale, commercial pet foods are invariably produced following stringent guidelines from either the National Research Council (NRC), the European Pet Food Industry Federation (FEDIAF) and the Association of American Feed Control Officials (AAFCO). Strict adherence to these guidelines ensures that manufactured pet foods should be balanced and safe for pets to eat. Guidelines (including full nutritional guidelines) are available to view or purchase from each organization’s website.

BARF adherents criticize these estimates, since the figures have been determined based on feeding trials using purified diets and therefore cannot be applied when raw food is offered. However, all the recommended figures include a margin of safety that takes into account digestibility for ready-to-eat foods, and although there are no figures available for raw foods at present, the NRC’s information is the best that is available. It is improbable that a dangerous over-supply may arise when BARF rations are calculated following NRC data, but in any case the minimum requirement or safe upper limit for supply as given by NRC can be used to evaluate BARF rations.

Some pet owners reject any food supplementation, such as extra minerals, as being “artificial”, and want to cover their pet’s requirements using exclusively “natural sources” such as fruit, vegetables, nuts and herbs. Note that the vitamin and trace element content in these products are usually broadly overestimated and the levels are too low to deliver an adequate supplement when using realistic doses. Much of the “science” behind the use of herbs has been carried over from traditional medicine practices and suggested beneficial effects are seldom tested in dogs and cats, with most of the claims being unproven in animals.

To formulate a BARF ration that covers all nutrient requirements based on single components and without the use of mineral and vitamin supplements is possible but complex, and should only be done with professional nutritional advice.

Various nutritional supplements based on herbs, algae, German medicinal clays (the so-called Heilerde or “healing earth”) and similar components are especially popular among dog owners and are viewed as natural sources of nutrients which contain unspecified “vital elements”. Normally any product statement for these products is inadequate or incomplete. Sometimes the composition is not given at all, and a nutritional analysis is almost always absent; such products cannot be recommended. The variety of available trace elements can vary widely; for example, although marine algae (brown sea kelp, Ascophyllum nodosum) is actually quite suitable as an iodine supplement, freshwater algae (Spirulina and Chlorella) contain no iodine. Lastly, the possibility of side effects and unwanted interactions from using these supplements cannot be excluded.

2. Hygiene risk from raw meat

Meat can contain viruses, bacteria and parasites. Aujeszky’s virus (pseudorabies) is the foremost risk and is deadly for both dogs and cats. Many pet owners know that raw pork should not be fed to their animals, as there are recent reports of hunting dogs dying from Aujeszky’s disease after contact with wild boar carcasses 8 (Figure 6), but all raw meat is potentially dangerous, especially when it has been prepared without observing basic food safety rules.

Possible bacterial pathogens include intestinal micro-organisms such as E. coli, Salmonella, Campylobacter and Yersinia, and endoparasites (e.g., tapeworms such as Echinococcus spp.) can of course infect dogs or cats. The human health risk must also be considered; as well as potentially pathogenic intestinal bacteria, raw meats can also (depending on their origin) carry zoonotic diseases such as tuberculosis or tularemia, and both farmed food animals and wild-living animals can be carriers of Toxoplasma.

BARF proponents will frequently counter these concerns with the argument that dogs and cats should be “immune” to such pathogens. Although it seems to be true that dogs and cats seldom suffer as much as humans from gastroenteritis related to Salmonella or E. coli bacteria, pet animals can indeed contract serious disease and even septicemia, with immune-compromised animals especially being at risk.

The bigger danger however is to human health, and it is not just that the handling of raw meat represents a risk (Figure 7). Dogs and cats that ingest contaminated meat can become symptom-free carriers and can shed human pathogens such as Salmonella in their feces for many weeks, allowing the bacteria to spread to the animal’s skin, its sleeping area, and finally throughout the household.

The hygiene risk due to raw meat is played down in almost all BARF publications. It may be that nowadays our food is generally so safe that potential dangers are almost eliminated and the awareness of risks is low. BARF products however are often not sourced from the human food industry. In addition, there is now a market whereby raw meat and meat by-products can be ordered online for use in BARF diets; such products are usually shipped frozen but are not subject to the same hygiene guidelines as food industry items, so there is no guarantee that the transport containers are always disinfected and that the cold chain is maintained. Furthermore, various raw commercial diets are currently available, and several reports have noted that these products are of poor quality in terms of microbiological contamination 9 10. It is of course worth noting that bacteria such as Salmonella are a risk in pet food factories too and that the pet food industry must maintain high standards to ensure quality and food safety are not compromised during the production process.

3. Problems caused by eating bones

Possible damage from ingestion of bones can include injuries in the mouth area and tooth fractures, bones lodging in the throat or esophagus, constipation, ileus, and even gastrointestinal perforation (Figure 8). There are no data on whether these problems have increased in recent years with the rise in the popularity of BARF diets, but some small animal practitioners and animal clinics have a subjective impression that these cases are being seen much more frequently nowadays compared to even five years ago, when they seemed comparatively rare.

4. Unsuitable and harmful ingredients

There is always the risk that an owner preparing a homemade diet may, through ignorance, employ ingredients that are poorly digestible or even poisonous. Although most dog and cat owners know that items such as chocolate, grapes and onions are poisonous, other products are often discussed, recommended and sold as being suitable for inclusion in BARF diets. A good example is garlic, which is often considered to have both health-promoting properties and a repellent effect against ectoparasites. Not only is there no scientific proof for this, garlic actually damages red blood cells. The same goes for broad-leaved garlic or chives, which are sometimes fed as “healthy herbal side-dishes”. Proponents will often respond to warnings by saying that such products are fed at well under the toxic dose, but it is not known if long-term intake of small amounts of such products are actually harmless or not, and therefore feeding all onion-type plants to dogs and cats must be advised against. Furthermore, it should be pointed out that some products are definitely not suitable for raw feeding, as follows:

• Eggs
  ­ - Raw eggs contain avidin, which binds biotin and leads to a biotin deficiency.
  ­-  Egg white contains a trypsin inhibitor which impairs protein digestion.
• Fish
  ­ - Many fish in raw form contain thiaminase, which destroys thiamin.
  ­ - Fish contain trimethylamine, an organic compound which binds iron and (if fed long-term) can cause anemia.
• Beans (Phaseolus genus)
  ­ - Contain lectins and tannins (which damages the gastrointestinal mucosa), trypsin inhibitors (which impair protein digestion) and cyanogenic glycosides (which can cause cyanide poisoning). However cooking or heat-treating such products renders them safe to use.
• Cassava/Manioc
  ­ - Uncooked contains cyanogenic glycosides. Again cooking or heat-treating such products renders them safe to use.

Specific concerns

It is worthwhile mentioning two specific problems attributable to BARF diets.

• Thyrotoxicosis; Studies have already shown 11 12 that dogs fed meat containing thyroid tissue can develop hyperthyroidism or thyrotoxicosis. In fact this is a problem which is not potentially unique to raw feeding, since thyroid hormones are heat stable, but BARF diets frequently contain meat sourced from the head and neck. In addition, the trachea and larynx are often sold as chew treats and may even be purchased as a canned product in some countries. Since no safe dose is known, such products must be regarded as unsuitable for feeding. To date, there are no reports of thyrotoxicosis on cats, perhaps because these products are rarely fed to cats.
  
  

• Detoxification; Some BARF promotional material may state that after changing from a ready-to-eat diet to raw food an animal may show digestive disturbances and skin problems. These are declared to be the animal undergoing “detoxification”, a process which must occur to eliminate “harmful chemicals” that have been ingested from ready-to-eat foodstuffs. This detoxification idea is a concept that comes from alternative medicine and has no scientific basis. However, digestive disturbances and skin problems can be signs of dietary intolerance, and the phenomenon perhaps exemplifies how convinced pet owners are of BARF, since they perceive these signs as positive, while the same reaction to a commercial ready-to-eat diet only confirms their negative opinion.

BARF for disease

If a sick animal is fed a raw diet it is important to consider if the characteristics of this feeding method (higher protein and fat content, high calcium and phosphorus levels, potential hygiene risk) are compatible with the nutritional demands imposed by a given disease.

• For gastrointestinal diseases, if the intestinal flora is disturbed and the intestinal mucosa can be assumed to have increased permeability, raw meat should not be given (especially if there is hematemesis and/or bloody diarrhea) in order to avoid any risk of infection. Raw feeding may be suitable for animals that need to lose weight or for diabetic individuals, and the raw fiber content can be increased if necessary with bran or cellulose.
  
  

• For kidney failure, BARF rations are contraindicated, as they are too rich in protein and phosphorus.

• In cases of neoplasia, pet owners often search in despair for a “miracle cure” and may consider feeding a “special” diet. If the patient is immunosuppressed, raw meat presents an avoidable infection risk and at least some carbohydrate is recommended in order to support the liver and supply the body with readily-available energy.

 Vitamin and trace element levels should not be ignored either when choosing a diet for an ill animal, as they are necessary for optimal functioning of the immune system.It must also be recognized that a change in diet represents an additional stress factor, and should not be imposed on tumor patients who frequently have little or no appetite anyway.

Summary

Whilst BARF is one possible form of feeding dogs and cats, it is associated with various risks. The veterinarian should explain these risks, but the ideological convictions and circumstances of the pet owner must also be taken into account. Owners like to make the “best” decision for their pet, but this is often not according to objective criteria, and is instead influenced by the internet, advertisements or other people. It is essential to advise careful selection and control of the foodstuffs chosen, since the recipes and recommendations found on the internet and in popular books are seldom correct. All food ingredients must be subject to strict hygiene criteria and owners must be aware of the specific risk of bacterial contamination when using meat sourced via mail-order companies; head or neck meat should not be used if thyroid tissue is present. In particular raw feeding must be advised against when at-risk individuals (small children, pregnant women, senior or chronically ill persons) live in the household, and for animals that are in frequent contact with such people, for example pets employed with animal-assisted therapy and education.

Further reading

• Freeman LM, Chandler ML, Hamper BA, et al. Current knowledge about the risks and benefits of raw meat-based diets for dogs and cats. J Am Vet Med Assoc 2013;243:1549-1558.