4 Jun 2018
Marge Chandler looks at what a raw food diet is, and its benefits and deficiencies for pets compared to commercial foods.
Marge Chandler
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Image: Manushot / Adobe Stock.
The practice of feeding raw foods to pets appears to be on the increase. In a US survey, 51% of owners claimed to feed raw foods (Morgan et al, 2017), and in a German survey around a third of owners said they fed some, or all, raw food to dogs, although only 8% said it was the only diet fed (Becker et al, 2012).
In a UK survey, 83% of dog owners had fed raw meat every day in the past month, although only 21% of dogs were fed solely raw meat (Courcier et al, 2010). Surveys may contain bias as they are generally voluntary and liable to be completed by owners with a special interest in the subject. However, in the US between 2012 and 2016 the raw food market grew from US$117 million to US$393 million, and raw diets as a percentage of new pet foods launched increased from 2% to 6.3% (Pet Food Industry, 2017).
Anecdotally, many pets appear to do well on these diets, although anecdotes are not evidence, and ample anecdotes and case reports also exist of nutritional deficiencies and contamination of raw food with bacteria and parasites.
Advocates of these diets claim health benefits, although none have been substantiated by research. Some owners are interested in feeding raw diets due to concerns about what commercial processed pet foods contain.
A lot of false stories exist about the ingredients of commercial pet foods – they do not contain road kill or dead pets. In Europe, many pet food producers are members of The European Pet Food Industry (FEDIAF). Members only use materials from species generally accepted in the human food chain, including beef, lamb, poultry, pork, fish, rabbit and game (FEDIAF, 2017).
Pet foods may contain offal or by-products. By-products are those parts of animals that are either deemed surplus to human consumption or not normally consumed by people in the UK. They are derived from animals slaughtered under veterinary supervision, inspected, and passed as fit for human consumption prior to slaughter. In the UK, animal by-products not intended for human consumption come under the EC regulation on animal by-products – for which Defra is responsible. Those assigned are the lowest risk rating, which requires the material be free of any transmissible disease and, therefore, excludes material from dying, diseased or disabled animals (www.food.gov.uk/business). In the EU, including the UK, by-products are usually listed as meat derivatives on the label. These ingredients may include organs such as lungs, heart, kidney or intestines (Figure 1).
Pet foods do contain antioxidant preservatives to slow the onset of rancidity. Some of them contain textured vegetable proteins and some contain colourings to make them visually appealing to owners. These are the same colourings added to processed human foods and are generally considered safe.
The use of meat ingredients often part of human diets competes with the human food chain, and can make both pet foods and human foods more expensive. If an animal is slaughtered for human consumption (or leather) and parts left are not used in other products, such as pet food, they need to be disposed of somehow. Landfills cannot contain the volume of product, and burying or incinerating products may risk water contamination and air pollution, along with a high output of carbon dioxide and ammonia (Meeker and Meisinger, 2015).
Owners may desire to feed a diet without by-products, preservatives, gums or thickeners, and some wish to avoid “fillers” without knowing what these might be. Carbohydrates, including fibre, which are nutrients, may be incorrectly thought to be fillers. Raw diets are often high in protein, which is believed to be beneficial by some owners, although is not necessary for most pets. They may wish to feed a more “natural” diet, although animals in the wild generally do not live as long as pets and need only reproduce to be successful as a species.
In a US survey, owners who fed raw diets had lower trust in veterinary advice than other owners and were more likely to rely on online resources than the veterinary team. Their perception was nutrition is not discussed at most veterinary consultations, and many of them did not trust their vet’s knowledge about nutrition. Many of the cat owners did not want their cat eating processed food. The dog owners considered their pets to be healthy, but also to have “food allergies”. Dog owners often wanted to feed a more “natural” and “healthier” diet (Morgan et al, 2017).
Firstly, no legal European definition exists of the term “natural“ for pet or human foods, although the Food Standards Agency provides guidance in that “natural” means the product is comprised of natural ingredients, for example, ingredients produced by nature, not the work of, or interfered by, man. The Association of American Feed Control Officials (AAFCO) requires, at minimum, the pet food be preserved with natural preservatives.
Some owners wish to feed their dog a diet that appears to be closer to what wolves naturally eat. Several problems exist with this. Wolves eat more parts of the carcase than many owners are willing to feed and also eat more per kilogram of bodyweight than most dogs can without becoming obese. Eating more provides more of the nutrients that could be deficient when less is fed. Finally, research has shown dogs have changed genetically from wolves, and are more able to digest starches and other carbohydrates (Aexelsson et al, 2013).
Raw foods can be roughly divided into three types: commercial, home-made and raw dried treats. Commercial raw foods are available that have been computer balanced to meet FEDIAF nutrient requirements, and should be complete and balanced. Most of these have not undergone feeding trials.
Home-made raw diets, unless at least computer balanced and supplemented, are almost invariably unbalanced and incomplete. A nutritional study of the bones and raw food diet showed it to be deficient in calcium, phosphorus, potassium and zinc, and excessively high in vitamin D (Freeman and Michel, 2001). It is likely some adult dogs could cope with some of these calcium and phosphorus imbalances, but they may result in developmental orthopaedic diseases if fed to growing animals. Zinc deficiencies may cause skin disorders and immune deficiencies. It is possible pets will not show deficiencies in the short term or if not stressed, and variation in individual susceptibility to disorders is likely.
Some of the home-made diet protocols are meant to balance the diet over a couple of weeks rather than for each meal or day. With the right blend of ingredients this could work; however, a study examining 200 recipes of home-made foods found 95% had at least one essential nutrient at levels below National Research Council or AAFCO guidelines and 83.5% had multiple deficiencies. Of the nine that were complete, eight were formulated by a veterinary nutritionist. This study also found the rotating diets – using evaluation of three recipe groups, each of which comprised seven separate recipes – did not eliminate deficiencies, so varying the foods may not balance out the deficiencies as many have the same deficiencies (Stockman et al, 2013).
Several studies in the US and Canada on bacterial contamination of raw foods, and shedding of bacteria in the faeces of dogs fed raw foods, have shown 20% to 35% of raw poultry and 80% of raw food diets for dogs tested positive for Salmonella, and 30% of the dogs’ stool samples were positive for Salmonella (Freeman et al, 2013). In the UK, Salmonella contamination of poultry was very prevalent in the 1990s, resulting in a programme that reduced prevalence to the targeted less than 2%.
In 2017, two suspected cases were discovered of salmonellosis in cats fed a raw frozen poultry commercial diet. Both cats presented with diarrhoea and vomiting. Salmonella species were found in the cats’ faeces and their diet (Giacometti et al, 2017). In some cats, salmonellosis can be a chronic febrile illness without specific gastrointestinal signs or as a localised tissue infection, so owners and vets may not be aware of it (Dow et al, 1989). Dogs fed Salmonella-contaminated raw food diets can also shed salmonellae without clinical signs and may be a source of environmental contamination, potentially leading to human or animal illness (Finley et al, 2007).
In 2018, a Dutch study found 20% of frozen commercial raw food diets contained Salmonella species (van Bree et al, 2018). In Canada, outbreaks have been reported of human salmonellosis related to exposure to animal-derived pet treats, involving pig ear treats, beef steak patty dog treats and pet treats of seafood origin (Finley et al, 2008).
Commercial canned food is processed to be sterile and unlikely to be contaminated before opening. Occasionally, contamination of commercial dry food with Salmonella has also been reported (Imanishi et al, 2014), although of the current US Food and Drug Administration (FDA) pet food recalls for Salmonella all of the 15 foods and treats were raw, freeze dried raw or dried raw products (US Food and Drug Administration, 2018).
The British Food Standards Agency reported 48.8% of chickens sold in the UK are contaminated with Campylobacter, with 6.5% having more than 1,000cfu/g (the highest level of contamination; Figure 2). These numbers have decreased over the past several years. Campylobacter species cause vomiting and diarrhoea among around 280,000 healthy people every year and can kill those with vulnerable immune systems. A study has concluded dogs are significant reservoirs of Campylobacter and contribute to human enteric infections, and chicken meat is a likely vehicle for the transmission of Campylobacter to humans (Workman et al, 2005).
In 2018, 27 dogs with suspected acute polyradiculoneuritis (APN) were found to be 9.4 times more likely to have faecal samples positive for Campylobacter species. Consumption of raw chicken was considered to be a risk factor – 96% of the APN cases ate raw chicken compared 26% of control cases (Martinez-Anton et al, 2018). Campylobacter can be reduced or eradicated with adequate freezing of the diet.
In humans, symptoms of listeriosis include fever, muscle aches and sometimes nausea or diarrhoea. If infection spreads to the nervous system, symptoms such as headache, stiff neck, confusion, loss of balance or convulsions can occur. Infected pregnant women may experience only a mild, flu-like illness, although the infection can result in miscarriage, premature delivery, serious infection of the newborn or stillbirth. In dogs it is often clinically silent, although it has been reported in association with abortion in dogs (Weber and Plagemann, 1991).
The van Bree et al study (2018) found Listeria monocytogenes in 43% of the samples of frozen commercial raw pet food. In a study of 480 dry and semi-moist samples, only one tested positive for Listeria grayi; however, of the 576 samples, raw food and jerky type treats, 66 were positive for Listeria (32 of those were Listeria monocytogenes) and 15 samples positive for Salmonella (Nemser et al, 2014).
A study of raw ground beef products showed samples had a 13.6% and 1.5% incidence of L monocytogenes and Salmonella species, respectively (Scanga et al, 2000). The main concern is a risk of Listeria spreading from pet faecal material, or the raw diets, to humans, especially pregnant women or immunocompromised people.
In the study by van Bree et al (2018), extended spectrum β lactamase (ESBL) producing Escherichia coli were found in 80% of sampled commercial raw diets. Salmonella strains isolated from raw diets have been reported to be resistant to up to seven antimicrobials (Finley et al, 2008). This is possibly due to gene transfer from bacteria such as E coli, which has been documented in a dog where the Salmonella-resistance phenotype of the dog was similar to that of an E coli strain isolated from the dog’s food (Strohmeyer et al, 2006).
In Sweden, 23 % of raw diets tested were found to have extended spectrum cephalosporins producing E coli (Nilsson, 2015) and a Dutch study found dogs eating raw meat were more likely to shed ESBL-producing Enterobacteriaceae (Baede et al, 2015). The presence of antibiotic-resistant bacteria in raw food diets, and in pet faeces, poses a potentially serious public health risk.
Parasitic contamination appears to be less problematic in raw foods than bacterial contamination. Parasites that may be present in raw meat include Toxoplasma gondii, Sarcocystis, Neospora caninum, Toxocara canis, Taenia and Echinococcus. The study by van Bree et al (2018) found 6% of frozen raw pet foods contained T gondii, 11% contained Sarcocystis cruzi and another 11% had Sarcocystis tenella.
Cases of canine Fanconi associated with eating jerky treats have been reported in Australia, the US, Japan and the UK (Bates et al, 2016; Yabuki et al, 2017; jerky may be cooked or dried to a temperature below that which decreases bacteria). Numerous products have been implicated – most originated from China although some have been from Europe.
The cause remains unknown despite FDA testing. A total of 11 of the cases in the UK reported to the Veterinary Poisons Information Service by 2016 included those where jerky treats were 5% to 25% of the dog’s diet. Some dogs had more than one type of treat, but reports included six reports each of chicken and duck treats, and one of beef (Bates et al, 2016).
Several reports have been made of dietary hyperthyroidism in dogs fed a raw meat diet, fresh or dried gullets or head meat (Köhler et al, 2012; Zeugswetter et al, 2013). This is usually reversible when the diet is changed.
In one study, the digestibility of fat, but not protein, was higher in a complete raw diet compared to one extruded dry diet. The raw diet was found to be palatable, but much lower in taurine and higher in phosphorus (Crissey et al, 1997).
A study in kittens also found some nutrients more digestible, although the serum albumin was decreased in those fed raw food, possibly in response to an increase in acute phase proteins (Hamper et al, 2016).
Another study showed cooking a raw meat diet did not alter apparent total tract energy and macronutrient digestibility, as well as deceasing the risk of bacterial contamination (Kerr et al, 2012).
In the van Bree (2018) study, only one brand out of eight included warnings and handling instructions on the package. In a US study of 60 raw diets, none provided food-borne illness warnings. Brands varied greatly in precautionary statements. Furthermore, none of the diets underwent feeding trials and nutritional adequacy substantiation was through formulation only (Mehlenbacher et al, 2012).
When handling raw foods, either in preparation for human or pet consumption, the cook must be scrupulous in hygiene – washing all surfaces and hands before touching anything or anyone. Cross contamination with food for human consumption is possible while preparing a raw pet diet. Bowls used for feeding should be cleaned, although standard methods of cleaning bowls, including scrubbing with dish soap and bleach, are inadequate to eliminate Salmonella (Weese and Rousseau, 2006). Small children, the elderly, pregnant women and the immunocompromised (for example, anyone ill or on immunosuppressive medications) should not handle raw meat.
Proponents of natural foods or feeding bones have claimed improvement in the cleanliness of pets’ teeth; further claims are sometimes made that feeding commercial pet food contributes to the prevalence of periodontal disease.
Several studies in dogs and cats have shown, while feeding bones may decrease cosmetic dental tartar, they do not decrease plaque or periodontitis and can increase the risk of tooth fractures (Steenkamp and Gorrel, 1999; Verstraete et al 1996; Clarke and Cameron, 1998).
Whole raw bones do not provide adequate calcium in the diet (Freeman and Michel, 2001). Another major risk is bones becoming stuck in, or perforating, the oesophagus, stomach or intestines. It is perceived feeding raw bones is safer than cooked bones, although no studies have examined this. If bones are chopped or ground small enough (for example, less than 0.5cm), they are less likely to get stuck, and bone meal will provide calcium and other minerals. Alternatively, consult a veterinary nutritionist to determine the amount of calcium (and other nutrients) to add to the diet.
Each clinic should have a policy on the handling of raw-fed pets, as they may shed infectious organisms or carry parasites. Some clinics do reverse barrier nursing or isolate the pet.
If a pet was to cause disease in another pet, client or staff member, the hospital may have some responsibility. The most at risk are post-operative patients, ones on chemotherapy or on prednisolone, or otherwise immunocompromised, the elderly, very young or the pregnant.
If an owner decides to feed a raw diet, he or she should make an informed decision. It is recommended hygienic care is used in handling the food and the dog’s faeces. Commercial diets should be better balanced. If the company is a member of the Pet Food Manufacturers‘ Association – which is the UK FEDIAF member – it will have at least agreed to meet FEDIAF nutrient requirements by computer balancing. In theory, commercial diets should carry less risk of contamination, although the van Bree et al (2018) study brings this into question. Advise owners to deworm their pets regularly. Ideally, the diet should be balanced by a veterinary nutritionist and supplemented, as necessary.
