Pet food 102: myths and misconceptions (Proceedings)

There are many myths and misconceptions about pet nutrition and commercial pet foods that are commonly propagated online, in written marketing material for various pet food companies, and by third party "non-biased" sources such as pet lover magazines. Many clients will believe the propaganda and develop strong opinions of various diets based on incorrect or misleading information. It is important for all veterinarians to understand which commonly repeated mantras are accurate versus those that are only used to sell product and to be able to effectively communicate this information to their clients. Below, some common myths are discussed and debunked.

By-products are bad

The American Association of Feed Control Officials (AAFCO) defines a meat by-product as "the non-rendered, clean parts, other than meat, derived from slaughtered mammals. It includes, but is not limited to, lungs, spleen, kidneys, brain, livers, blood, bone...and stomachs and intestines freed of their contents. It does not include hair, horns, teeth and hoofs...If it bears name descriptive of its kind, it must correspond thereto".

Chicken by-product is defined as "ground, rendered, clean parts of the carcass of slaughtered chicken, such as necks, feet, undeveloped eggs and intestines, exclusive of feathers, except in such amounts as might occur unavoidable in good processing practice." While many Americans may feel uncomfortable with these types of foods in their own diets, it is important to realize that in many cultures, these parts are regularly consumed and often even considered to be delicacies! Some of these items may be very high in nutrients (e.g. organ meats, undeveloped eggs). Furthermore, when dogs and cats have access to whole prey, they often eat these parts *first*.

It has become common for many manufacturers to advertise that their foods do not contain "by-products" and also to give definitions of by-products on their websites or written advertisements that differ substantially from the legal AAFCO definition. For example, several websites list by-products as including road kill, "euthanized dogs and cats including collars", hooves, hair, and teeth. Other manufacturers include ingredients that could be considered by-products – such as liver – and list it simply as liver, rather than as a by-product, then advertise that they contain no by-products. By-products can definitely vary in quality and the consumer has to trust the manufacturer to use a high-quality product (many ingredients vary greatly in quality, so this is often the case, not just with by-products). Good manufacturers are very particular about their suppliers and inspect every shipment and perform analytical testing to ensure that it meets their nutrient specifications.

Bacteria in raw meat doesn't make dogs or cats sick

There is a plethora of misinformation regarding the safety of raw diets for pets. Many producers and promoters of raw diets either deny that their products potentially contain pathogenic bacteria such as Salmonella or E.coli or state in their marketing materials that animals do not get sick from these bacteria. It has been impossible not to notice that there have been numerous large scale recalls in the past few years of meat intended for human consumption due to contamination with pathogenic bacteria. A New York Times article in October 2009 highlighted concerns with contamination of ground beef1. In February 2010, a major raw food producer recalled one of its raw chicken diets due to suspicion of contamination with Salmonella 2. A Consumer Reports investigation, published in 2010, found Campylobacter and/or Salmonella in 2/3 of the chicken (including organic) purchased from major grocery retailers. These are just a few examples of the widespread problem of bacterial contamination of meat. It is safest to assume that all raw meat is contaminated, whether intended for human or animal consumption.

While it is true that dogs and cats may be less sensitive to food borne illness than people, there are numerous documented cases of severe and even fatal disease attributed to bacterial contamination of foods3-5. Additionally, it is likely that many milder cases go undiagnosed as the clinical signs – vomiting, diarrhea, ± fever - are far from pathognomonic. Despite some manufacturers' claims, there is no evidence that washing meat in hydrogen peroxide or grapefruit seed extract renders it sterile. Moreover, one study demonstrated that most methods that people use to sanitize pet dishes after feeding raw meat were inadequate to kill pathogenic bacteria6. Although some diet manufacturers have started using high pressure processing (HPP) to kill bacteria in raw diets, this technique is rather new to the pet food industry and its efficacy is still unclear.

In addition to concerns with pet illness, direct contact with contaminated pet treats7 has been linked to human infections with pathologic bacteria. As in pets, it is likely that many other milder infections go undiagnosed and therefore unreported. There is even greater risk to people from contact with animals that consume diets contaminated with pathogenic bacteria. Raw food-fed pets have been shown to shed viable pathogenic bacteria8-10, sometimes asymptomatically, putting all people in the household at risk. Of particular concern are households with young children, the elderly, or people with weak or suppressed immune systems (such as the elderly and HIV or cancer patients).

It is important to keep in mind that while many clients (and even some veterinarians) may believe very strongly in the benefits of raw-feeding, there is no scientific evidence to substantiate any of the anecdotal benefits of raw feeding over feeding a cooked diet. However, there is significant evidence to suggest that these diets and raw meat treats can cause harm to both pets and their human companions.

Grains are bad for dogs and cats

Another common myth is that dogs and cats lack the necessary enzymes to digest grains and that grains cause allergies, obesity and other health problems. Of the grains, corn is most often maligned. The truth is that properly cooked grains are generally well utilized by both dogs and cats. Each grain has a distinct nutritional profile and differing amounts of protein, fat, vitamins and minerals as well as amounts and types of fiber. It is overly simplistic to make blanket statements that apply to all grains as there are few strict commonalities that would lead an animal to react adversely to the entire group as a whole.

While corn allergies have been occasionally documented, they likely reflect corn's widespread inclusion in commercial diets rather than enhanced allergenicity. In the author's experience, most "corn allergic" dogs are not truly allergic. Diagnosis of food allergies is complicated by the lack of accurate testing modalities other than exclusion and re-challenge. In addition, many diets contain multiple common protein sources (e.g. corn, wheat, beef, dairy and chicken), meaning that any one of those proteins could be causing the reaction and it can be difficult to figure out which ingredient is the problem without a structured re-challenge which tends to be a hard sell to owners. There is also no evidence to support claims that corn (or any other grain) is responsible for health problems outside of the rare dog with a true allergy.

Many "grain free" dry diets simply substitute potato or tapioca for the grains that would otherwise be in the diet. Typically, these diets contain similar amounts of carbohydrates as grain-containing diets. Interestingly, while whole grains contain many vitamins, minerals and various types and amounts of fiber, potatoes and tapioca are relatively pure starches which contribute minimal amounts of most nutrients while having high glycemic indices in humans and presumably in pets, as well. These ingredients tend to fit the definition of "filler" (providing minimal nutrients) much better than most grains. Moreover, substituting potato or tapioca for whole grains may actually defeat one of the touted benefits of grain-free diets – fewer simple carbohydrates.

Flax is a good source of omega-3 fatty acids

As research shows numerous health benefits of omega-3 polyunsaturated fatty acid (PUFA) supplementation in humans and animals, many pet food companies have begun to supplement their diets with omega-3 fatty acids and include this information in marketing materials.

There are two main types of omega-3 fatty acids – short chain (α-linolenic acid, ALA, 18:3) and long chain (eicosapentaenoic acid, EPA, 20:5, and docosahexaenoic acid, DHA, 22:6). ALA is produced by terrestrial plants and can be found in flax, canola, walnuts, and other seeds and seed oils. EPA and DHA are found only in certain marine plants and in cold water wild-caught marine fish such as cod, salmon, and anchovies. While most mammals possess the enzyme (delta-6 desaturase) necessary to convert ALA to EPA and then DHA, this conversion process is uniformly poor in the species that have been studied – conversion rates range from 1-15%. Cats in particular have very low activity of the necessary enzyme and are unlikely to be able to produce clinically relevant amounts of the long chain omega-3s, regardless of the ALA concentration in the diet. (This low enzyme activity also is responsible for the essentiality of arachidonic acid (20:4 n-6) for cats, as it is produced from linoleic acid (18:2 n-6) using the same enzymatic pathway)

The vast majority of the veterinary research demonstrating benefits of omega-3 fatty acid supplementation has investigated supplementing EPA and DHA directly rather than ALA. To attempt to duplicate the tissue EPA and DHA concentrations using only ALA, 6 – 10 times the amount of EPA and DHA would have to be provided as ALA (for dogs). As fats contribute between 8.5-9 kcal per gram, this is a difference of as much as 81 kcal per dose based on a one gram daily dose (a small dog or cat may only consume 250 kcal per day). Additionally, omega-3 fatty acids of all types are prone to oxidation secondary to their multiple double bonds (polyunsaturation). High amounts of these fats of all varieties require careful attention to antioxidant provision and diet storage. It may be safer to use smaller amounts of concentrated long-chain omega-3s rather than large amounts of ALA.

It is important to examine the ingredient list of any foods that advertise omega-3 fatty acid supplementation to ensure that this supplementation is mainly in the form of EPA and DHA. Other ingredients that may indicate higher levels of EPA and DHA include fish oil, salmon oil, cod liver oil, fish meal, herring meal, and algal meal. The best way to determine the amount of omega-3 fatty acids in a diet is to contact the manufacturer and ask specifically about total omega-3, DHA and EPA concentrations. If there is a large difference between total and DHA + EPA concentrations, the remainder is likely ALA, even if typical sources of ALA (e.g. flax, canola oil) are not included in the ingredient list.

Natural diets are better

AAFCO defines natural as "a feed or ingredient derived solely from plant, animal or mined sources, either in its unprocessed state or having been subject to physical processing, heat processing, rendering, purification, extraction, hydrolysis, enzymolysis or fermentation, but not having been produced by or subject to a chemically synthetic process...". To label a pet food as "natural" requires that no synthetic compounds of any kind be included. However, phrasing such as "natural diet with added vitamins" can be used to acknowledge the fact that many diets contain natural ingredients but are supplemented with synthetic vitamins, amino acids or mineral complexes.

The current definition of natural gives little information about ingredient or product quality as rotten meat or leather (to make an extreme point) would be defined as natural whereas synthetic taurine would make the diet "unnatural". Natural sources of many vitamins, minerals and amino acids used in commercial pet foods are not always practical and many synthetic sources are metabolically indistinguishable from natural forms. Some commercial diets attempt to provide for all required nutrients using only whole foods. This approach, while emotionally appealing, presents several problems. First, these diets generally contain large numbers of ingredients sourced from many different vendors. Vitamin and mineral contents of ingredients such as fruits, vegetables and kelp (a commonly used iodine source) tend to vary sometimes substantially between sources and even by season. Therefore, a diet that meets all nutrient requirements in one batch may not meet them for the next batch, unless all the ingredients are analyzed with each batch and the appropriate safeguards built into the formulation. Ingredient analysis can be quite expensive, so it is common that individual shipments of ingredients may not be thoroughly screened, especially by smaller companies that purchase many different ingredients and lack the ability to do in-house analysis.

Whole food ingredients never provide only one nutrient, thus adding enough of a food to meet one nutrient requirement can result in an excess of another nutrient. Similarly, some ingredients such as taurine become less bioavailable with cooking (others become more available); it may be difficult or impossible to provide adequate amounts of these nutrients from whole food sources without altering the nutrient profile of the whole diet.

Additional ingredients also increase cost and can complicate diagnosis of food intolerance or allergy if the pet ceases to tolerate the diet. Synthetic vitamins and minerals, despite their chemical sounding names, should not be cause for concern. In fact, inclusion of these supplements increases the likelihood that the diet will provide all the essential nutrients required for a particular life stage.

Artificial preservatives are becoming uncommon in pet foods, mostly due to public opinion rather than any documented adverse effects. While there are many "natural" antioxidants such as vitamin C, vitamin E (mixed tocopherols), and rosemary extract that can be used in pet foods, these preservatives tend to be less effective than their synthetic counterparts and necessitate more attention be paid to setting appropriate expiration dates, proper storage and monitoring for spoilage.

References

Moss M. E.Coli Path Shows Flaws in Beef Inspection. The New York Times. New York: The New York Times Company, 2009.

Nature's Variety Issues Nationwide Voluntary Recall On Raw Frozen Chicken Diets With A "Best If Used By" Date Of 11/10/10: FDA, 2010.

Chengappa MM, Staats J, Oberst RD, et al. Prevalence of Salmonella in raw meat used in diets of racing greyhounds. J Vet Diagn Invest 1993;5:372-377.

Morley PS, Strohmeyer RA, Tankson JD, et al. Evaluation of the association between feeding raw meat and Salmonella enterica infections at a Greyhound breeding facility. J Am Vet Med Assoc 2006;228:1524-1532.

Stiver SL, Frazier KS, Mauel MJ, et al. Septicemic salmonellosis in two cats fed a raw-meat diet. J Am Anim Hosp Assoc 2003;39:538-542.

Weese, J. S. and J. Rousseau (2006). "Survival of Salmonella Copenhagen in food bowls following contamination with experimentally inoculated raw meat: effects of time, cleaning, and disinfection." Can Vet J 47(9): 887-889.

Human Salmonellosis Associated with Animal-Derived Pet Treats - United States and Canada, 2005. MMWR Weekly. Atlanta, GA: CDC, 2006.

Lefebvre SL, Reid-Smith R, Boerlin P, et al. Evaluation of the risks of shedding Salmonellae and other potential pathogens by therapy dogs fed raw diets in Ontario and Alberta. Zoonoses Public Health 2008;55:470-480.

Finley R, Ribble C, Aramini J, et al. The risk of salmonellae shedding by dogs fed Salmonella-contaminated commercial raw food diets. Can Vet J 2007;48:69-75.

Lenz J, Joffe D, Kauffman M, et al. Perceptions, practices, and consequences associated with foodborne pathogens and the feeding of raw meat to dogs. Can Vet J 2009;50:637-643.