There are numerous arguments over the health effects of feeding commercial pet foods, and many raw feeding pet owners claim to have noticed a significant increase in overall health after switching to a raw food diet. The number of raw feeding owners who make these observations over the life-time of their pet far exceeds the numbers of pets required to complete an in-house commercial pet food trial (6 out of 8 starters) that runs for 6 months only according to AAFCO guidelines.
Commercial pet foods, dry foods in particular, often contain a large amount of grains, which proponents of grain-free food feel are inappropriate for carnivorous dogs and cats. Because cats are obligate carnivores, it is believed that a switch to a predominantly meat based raw diet would be especially beneficial (as compared to a raw diet for dogs) due to cats' relative inability to digest grains. Studies comparing the source of protein in dry cat food concluded that the digestibility of meat-based protein is superior to corn-based protein.
Because commercial pet foods are assumed to be the primary or exclusive element of a pet's diet, manufacturers enrich their product by supplementing the food with vitamins and minerals. As the heat used to process commercial pet foods may reduce the level of naturally occurring nutrients, critics question the actual nutritional value of commercial foods. Critics argue that there may be elements to pet nutrition yet to be discovered or that are not understood well enough to be supplemented. There is skepticism over the efficacy of supplements vs the natural absorption of naturally occurring nutrients. The same rationale is used by some to reject supplemented home cooked pet food. A study involving rats has suggested that the digestibility of the amino acids in cat food is altered during heat processing.
Raw food proponent Dr Ian Billinghurst (owner of the registered trademark 'Barf Diet' and the BARF World Distributor Network) argues in his books that the dog has evolved over many million years on a natural raw diet and logically, this is the ideal food source. He claims that processed foods are "not what [the] dog was programmed to eat during its long process of evolution" and says that foods similar to those eaten by the dog's wild ancestors are more biologically appropriate.
Critics have pointed out the flaws in associating "natural" with better and Billinghurst himself warns against that stating "There are grave dangers that go along with the natural diet and natural conditions the ancestors or wild cousins of our dogs live with." Katie Merwick, who runs an animal rescue sanctuary cautions against "making a fetish out of what animals eat in the wild"[paraphrased].
One study used to back up the claims of raw food being superior to cooked food is Francis M. Pottenger, Jr.'s study of 900 cats over a period of 10 years from 1932 to 1942. His results showed that cats that were fed 2/3 raw meat, 1/3 raw milk and a small amount of cod liver oil were disease free and healthy while those fed the same food with the meat cooked developed degenerative diseases and reproductive difficulties, with new generations plagued with health problems. The study was done before the importance of taurine in a cat's diet was known and it has been suggested that the group of Pottenger's cats on cooked food simply suffered from taurine deficiency as heating or cooking food causes a reduction in taurine content. In a study on feline maternal taurine deficiency, the group of taurine-deficient cats exhibited symptoms similar to the Pottenger's cats on a cooked diet.
There are various differences in opinion within the raw feeding community. Issues include the question of whether dogs are omnivores or carnivores. Also, whether cats and dogs need plant material in their diet, and if so, the proportion of such material. The safety of whole bones is also a frequent topic of discussion. Recipes that are advocated range from those that include vegetables and grains, to a minimalist approach using only meat, bones, organ meat, and necessary supplements such as the Meat with Bone diet advocated by Michelle T. Bernard.
Veterinary Surgeon, Tom Lonsdale, was one of the earliest advocates of feeding pet carnivores a species-appropriate diet best approximated by the Raw meaty Bones diet. His 1992 book Raw meaty Bones book was nominated for an Australian Veterinary Association Award for pointing out the link between inappropriate diets and periodontal disease that can lead onto other systemic illnesses. Tom Lonsdale's later book Work Wonders was written after many requests from owners for an easy-to-follow read rather than his extensively referenced and scientifically written early book Raw meaty Bones which was written more with the veterinary profession in mind.
The "BARF" diet, an acronym for Biologically Appropriate Raw Food or Bones And Raw Food was created by Billinghurst. The acronym was coined by Debra Tripp. A typical BARF diet is made up of 60-80% of raw meaty bones (RMB), that is bones with about 50% meat, (e.g. chicken neck, back and wings) and 20-40% of fruit and vegetables, offal, meat, eggs, or dairy foods.
The "prey model" diet attempts to simulate the proportions of an actual prey animal in a pet's diet. Actual whole prey are used whenever possible, including whole rabbits, chickens, game hens and turkeys. Generally, the diet recommends 80% meat (including some 'meaty' organs such as heart), 10% bone and 10% organs (of which half is liver). Proponents of the whole prey model diet believe dogs and cats are both natural carnivores and therefore there is no nutritional or dietary need for anything other than meat, bones, and organs. The supporters of the prey model also focus on feeding meats from a wide variety of animals. Some also add small amounts of vegetable matter to simulate the consumption of stomach contents of prey animals.
Supplements are generally not used in a prey model diet although some followers do add fish oil to the diet to compensate for the reduced amount of omega-3 fatty acid in commercially raised grain-fed livestock. This problem can be partially mitigated by using grass-fed meat, which has more than double the omega-3 content as grain-fed meat.
The nutritional balance of a raw diet can vary greatly depending on the recipe. Some raw diet proponents prefer to use a variety of ingredients, believing that will provide a more balanced diet than a single primary food.
The Association of American Feed Control Officials (AAFCO) provides standards that guides many commercial pet food companies, a level of supervision that does not occur with homemade food. One study analyzed the nutritional content of three homemade diets (BARF, Ultimate and Volhard) and two commercial raw food diets (Steve's Real Food and Sojourner Farms) and compared it to the AAFCO standards, showing nutritional imbalances in the homemade diets. Three of the diets had abnormal calcium-to-phosphorus ratios which can lead to hyperparathyroidism and fibrous osteodystrophy in puppies.
Some proponents of raw diets recommend consultation with a veterinarian or animal nutritionist to verify that proper nutrients are being ingested, others dismiss the importance of AAFCO standards, claiming that AAFCO certification is not indicative of the quality of a diet.
Raw bones fed to dogs contain high amounts of calcium and phosphorus that is essential for neuromuscular, cardiovascular, immune, endocrine and clotting function. The ratio of calcium to phosphorus for adult dogs should be 1:1. Compared to commercial dog food, the raw food diet allows dogs to work for their meal, ripping the meat off bones and then gnawing at the bones. In regards to dental health, bone to tooth gnawing allows a dog to rid their teeth of plaque buildup promoting good oral health. Skeptics argue however that this isn't healthy for dogs and it can cause dental fractures.
The use of whole bone creates a risk of dental fractures, intestinal obstruction, gastroenteritis, and intestinal perforations. Wolf care managers questioned on the topic of feeding bones identified the presence of animal hide with hair as offering some protection from intestinal perforation in the wild. An analysis of the skulls of African wild dogs showed that the natural diet of wild carnivores does not prevent them from suffering the same oral disease as their domestic counterparts.
While the intense heat used in manufacturing pet food or cooking meat destroys any potential bacteria, raw meats may contain bacteria that are unsafe for both dogs and cats. The United States government reported that in 2006, 16.3% of all chickens were contaminated with Salmonella. A study on 25 commercial raw diets for dogs and cats detected salmonella in 20% and Escherichia coli in 64% of the diets. However, the E. coli strain that can cause severe illness O157:H7 was not tested for. An example of the severity of E. coli H157:O7 infections can be seen in affected greyhound racing dogs fed raw meat as part of their diet. Known in greyhounds as "Alabama rot", the disease causes severe vasculitis, cutaneous necrosis, renal failure and death. A contributing factor might be that racing greyhounds are typically fed raw meat classified as "not for human consumption", which may contain higher than normal levels of bacteria.
Raw feeders claim that the stomach enzymes and short intestinal tracts of dogs and cats allow them to handle harmful bacteria. There has been a reported case where two cats fed a raw diet developed salmonellosis and died as a result. A veterinarian from the National Animal Poison Control Center suggests that the diarrhea in animals that raw feeders attribute to detoxing could be caused by pathogens such as Salmonella, E. coli, Clostridium and Campylobacter. Bacteria proliferation in any meat can be reduced by following proper food safety practices such as defrosting meat in the refrigerator; harmful bacteria can be largely eliminated from meat by cooking.
Raw meats may also contain harmful parasites. As with bacteria, these parasites are destroyed during the heat processing of cooking meat or manufacturing pet foods. Some raw diet recipes call for freezing meat before serving it, which greatly reduces (but does not necessarily eliminate) extant parasites. According to a former European Union directive, freezing fish at -20 °C (-4 °F) for 24 hours kills parasites. The U.S. Food and Drug Administration (FDA) recommends freezing at -35 °C (-31 °F) for 15 hours, or at -20 °C (-4 °F) for 7 days. The most common parasites in fish are roundworms from the family Anisakidae and fish tapeworm. While freezing pork at -15 °C (5 °F) for 20 days will kill any Trichinella spiralis worm, trichinosis is rare in countries with well established meat inspection programs, with cases of trichinosis in humans in the United States mostly coming from consumption of raw or undercooked wild game. Trichinella species in wildlife are resistant to freezing. In dogs and cats symptoms of trichinellosis would include mild gastrointestinal upset (vomiting and diarrhea) and in rare cases, muscle pain and muscle stiffness.
A survey of accredited zoos worldwide showed a slightly increased risk of parasites and diseases in animals that are carcass fed as compared to commercial food fed. However, the researchers suggested that that may be caused by increased opportunistic preying and infected live preys may be the source of contamination.
A possible risk of raw feeding is that of human infection caused by direct or indirect exposure to bacterial pathogens in raw meat and animal stools. For example, the British Veterinary Association warns that humans "risk exposing themselves to bacteria like Salmonella". A small study on the levels of salmonella in the stool of 10 dogs that ate a raw diet found that 80% of the raw diet tested positive for Salmonella and while 30 percent of the stool samples from dogs fed a raw food diet contained salmonella, none of the control dogs (commercial feed) contained Salmonella. The authors of the study concluded that dogs on a raw food diet may therefore be a source of environmental contamination, although they caution about the generalizability of their results due to the small number of dogs studied.
While raw dog food can contain Salmonella, commercial dog food is not free from it. Centers for Disease Control and Prevention released a general warning about contamination of commercial dry dog food and treats by Salmonella.
Because of the potential animal and human health risks, veterinarian organizations and public health agencies assert that the risks inherent in raw feeding outweigh the purported benefits. Despite such concerns, there is no known incidence of humans being infected with salmonella by cats and dogs fed a raw diet.
After the 2007 pet food recall, interest in homemade pet food (both cooked and raw) grew tremendously. As a result of that, several pet food manufacturers now offer frozen raw diet products for pet owners. Some consumers believe that many of the same issues they find with commercial pet foods exist with packaged raw diets, others use it due to its convenience and for products with AAFCO certification.
The commercial raw pet food market is estimated to be worth $169 million a year (2007 figures), less than 1% of total pet food sales figure in North America($18 billion). Growth is estimated at 23% per annum.
Many commercial raw pet food manufacturers now use High Pressure Pasteurization (HPP), a process that kills pathogenic bacteria through high-pressure. High Pressure Pasteurization is a USDA-approved food processing technique.
Veterinary associations such as the American Veterinary Medical Association, British Veterinary Association and Canadian Veterinary Medical Association have warned of the animal and public health risk that could arise from feeding raw meat to pets and have stated that there is no scientific evidence to support the claimed benefits of raw feeding. While lack of favorable evidence can result from lack of long-term studies investigating the effect of eating a balanced raw diet, a minority of holistic-oriented veterinarians recommend raw feeding because of clear health benefits they observed over the years in raw fed dogs. Dr Tom Lonsdale in Australia has been a long-time and prominent veterinary advocate of raw feeding.
In 2007, The Sydney Morning Herald reported that the RSPCA Australia President Dr. Hugh Wirth has stated that veterinary associations in Britain and Australia make a "compromise" and advocate some feeding of raw bones to dogs. This contradicts the contemporaneous warnings put out by the BVA against feeding pets raw bones.