Pet food ingredients: Good, bad and ugly (Proceedings)


The trend in the media, on web sites, and other sources of information on the topic of human nutrition to identify particular foods as "good" or "bad" is confusing at best.

The trend in the media, on web sites, and other sources of information on the topic of human nutrition to identify particular foods as "good" or "bad" is confusing at best. Unfortunately, that trend appears to have become common in discussion of pet nutrition as well. Much opinion can be found to either praise or malign a particular food or food ingredient. Depending on the source or the findings of a particular study, some substances are both "good" and "bad." Most often, the positive or negative effect of a food on health is related to dose. However, that factor is often lost in discussion of the effects of an ingredient on health.

Occasionally, petfood consumer advocates will decide to attack the safety or value of a petfood ingredient based on little pertinent data but much speculation and innuendo. This occurred with the antioxidant preservative ethoxyquin in the early 1990's. A web site seemingly devoted to the total removal of menadione (a synthetic source of vitamin K activity) from petfoods has many companies nervous. However, it appears that it is the petfood companies themselves that often drives the consumer's concerns regarding petfood ingredient safety. Eager to distinguish themselves from competitors, it is the marketing strategy of some companies to disparage the safety and wholesomeness of other products on the market. Even without accompanying explanations, simple statements of "no this!" or "that-free!" leads the consumer to question why a perfectly legitimate ingredient with a long history of safe use is in the other product, and to fret over what harmful effects that may have on their pets. At the same time, companies may laud the inclusion of ingredients for which there are no appreciable data or experience to show safety as used. In fact, many times the ingredient isn't even approved for use in animal feeds or petfoods.

While "good" or "bad" doesn't appear appropriate to describe most legitimate ingredients, some sure are "ugly." For example, "meat by-products" connote all sorts of unappealing perceptions, while it includes many parts that humans do eat themselves (e.g., livers, but also intestinal casings, thymus, kidneys, brains and blood). Other components of meat by-products may include things humans do not eat, such as spleens, udders and bone. While unappetizing to most people, they still can be legitimate sources of nutrition, and if processed correctly, consumed safely by pets.

Petfood ingredient approval methods

Under the law, all ingredients in petfoods must be either GRAS (generally recognized as safe) substances, approved food additives, or otherwise sanctioned for its intended use in animal feed.

Food additives may be "direct" or "indirect" food additives. Examples of the former include preservatives and other substances intended for technical effects on the food, but may also include nutrients such as selenium. For regulatory purposes, irradiation of food or feed is considered a direct food additive. Indirect food additives include packaging and other food contact materials, food equipment lubricants, and other substances that may become a component of the final product. A food additive must be approved by FDA prior to use in petfood. Extensive data must be submitted to characterize the nature or the substance, to document methods of manufacturing, and to demonstrate both utility and safety. Aspects of safety reviewed include acute and chronic toxicity, carcinogenicity, teratogenicity and mutagenicity. Limits or restrictions on levels in products, types of products, intended species, etc., are spelled out in the resulting regulation.

GRAS substances include a codified list of ingredients in the FDA regulations, primarily of ingredients found to be of common use in foods or feeds prior to the change of laws in 1958 that established the food additive approval process. This includes many spices and other flavoring agents, nutrients, and other substances intended for technical effects on the food (e.g., preservatives, anticaking agents, emulsifiers, gums). The regulations note that not all ingredients that would be GRAS can be codified, though. Substances commonly thought of a "food" (e.g., salt, vinegar) or has a long history (i.e., pre-1958) of safe use in diets of animals are most often considered GRAS. Thus, many of the ingredients listed in AAFCO that may stem back to as far as 1909 may in fact be GRAS, but simply are not formally codified as such.

For a substance without an established history of safe use to be determined as GRAS, scientific studies equivalent in quality and extent to what would appear in a Food Additive Petition must be available. The major difference is that in the case of a GRAS substance, the supporting data must be predominantly in the publicly available literature. Historically, companies would submit a GRAS Affirmation Petition similar to a Food Additive Petition, and FDA would approve or not approve. In human foods, a GRAS Notification system has been put in place, wherein a company convenes a panel of experts to review all available safety data and reaches a consensus as to the substances safety. The company then provides this information to FDA, which then has a specified period to disagree with the panel's conclusions. However, to date, FDA has not been accepting GRAS Notifications for animal feed ingredients.

Historically, the establishment of an AAFCO Feed Ingredient Definition was a potentially quicker and less arduous means by which ingredients could be sanctioned for use in animal feeds and petfoods. FDA was intimately involved in the process, especially with regard to safety determinations, so while the ingredient was not formally "approved," it was permitted on the market. However, FDA and AAFCO have recently made an agreement whereby FDA assumes even more direct control of the definition process, and has final sign-off on all new or modified ingredient definitions.

A tale of two additives

Ethoxyquin is a food additive approved in the late 1950's for use as an antioxidant preservative to prevent degradation of fats and fat-soluble vitamins in animal feed. Its inclusion in petfoods went unquestioned until the late 1980's, when several consumers implicated its use with the occurrence of cancer, liver failure, immune system problems, and a host of other adverse effects in dogs. The scientific literature failed to support these reports (Dzanis, 1991). Further study by the company found reversible changes to serum liver enzyme levels and inclusions of a heme-related pigment in the livers of dogs fed the highest amounts of ethoxyquin in the diet. No other adverse effects were observed. As a result, FDA asked dog food companies to voluntarily reduce inclusion rates from a maximum of 150 ppm to 75 ppm, but other than that, no other action has been taken. Despite that lack of regulatory concern, consumer and competitor pressures have forced its removal from the majority of pet foods on the market today.

Propylene glycol is a GRAS substance used to help retain moisture in semi-moist petfoods. It was known since the 1970's to cause Heinz body formation in the red blood cells of cats, but could not be associated with anemia or other clinical manifestations. Studies in the 1990's, however, showed a decrease in the red cell half-life, increased sensitivity to other oxidants, and other adverse effects. As a result, FDA modified the regulations so that propylene glycol was not GRAS for intended use in cat foods (Dzanis, 1994). Small amounts may still be present as a result of use as a carrier for fat-soluble vitamin premixes, but those levels are well below any observed effect, including effect on Heinz body formation. Through it all, there was never a concern expressed by pet owners or others regarding the safety of propylene glycol for this use.

Other ingredient issues

Corn or corn products are often considered inferior to other grains such as rice, both in terms of nutritive value and potential allergenicity. Wheat is often placed in the same category as corn. While rice is generally more digestible, that also means the starches are reduced to sugars and absorbed much more quickly than for corn. This could be good or bad, but may not be desirable for animals with clinical problems related to blood glucose control (i.e., diabetics). As far as potential allergenicity, historical use of rice in therapeutic diets as a "novel ingredient" for diagnosis or control of food allergies may have led to a false impression. In cases where the cause of a food allergy has been determined, the incidence of allergy to corn is equivalent to the incidence of allergy to rice (Cowell et al., 2000).

The incident of contamination of wheat gluten with melamine that led to the massive recall of petfoods in 2007 has led to concern about any use of it or similar ingredients. In fact, the adulterated ingredient was not wheat gluten at all, but wheat flour that was intentionally spiked with a non-protein nitrogen source to falsely elevate apparent protein levels. This illegal and condemnable act does not diminish the utility of wheat gluten, other wheat products, or other sources of gluten. While wheat-sensitive enteropathies may be a legitimate concern in some breeds of dogs, in most cases it is not an issue.

Many opponents of the petfood industry cite existing AAFCO definitions as proof of unsuitable materials in petfoods. Granted, some names evoke unpleasant reactions, such as "restaurant food waste" (AAFCO #60.97), "dried poultry litter" (AAFCO #74.3) and "unborn calf carcasses" (AAFCO 9..67). Properly processed, these ingredients may be very useful in animal feeding (e.g., poultry litter as a source of non-protein nitrogen and fiber to ruminants), but simply have no use in petfoods. Regardless, what opponents fail to note is that if these ingredients were in a petfood, by law they would have to be declared on the label by their official AAFCO names. However, those ingredients are never seen on petfood labels, hence can be reasonably assumed not to be in petfoods.

Opponents also frequently assert the presence of dog and cat carcasses in petfoods, a premise that the industry vehemently denies. Rendering of euthanized dogs and cats has been used as a means of disposal. Since there are many other uses for rendered materials other than animal feed or petfood, and the source of rendered material dictates the possibility of it containing dog or cat carcasses (e.g., a rendering plant dedicated to a slaughterhouse facility vs. a general dead animal pick-up service), there simply is no incentive for petfood companies to use rendered products that may contain these materials. Still, regulators cannot unequivocally confirm these materials are never used. FDA conducted an analysis of numerous petfoods several years ago, and has posted results on its web site. Trace amounts of pentobarbital have been found in some petfoods, although only at levels well below what would have any physiologic effect on the animal consuming the product. Since some products with minor residues did not contain ingredients that would be a likely source of pentobarbital, FDA could not fully explain its findings. However, samples were also analyzed for the presence of dog or cat specific proteins. No evidence could be found of any dog or cat material in any petfood.

Selected references and sources of information

Dzanis DA. Safety of ethoxyquin in dog foods. J Nutr 121:s163-164, 1991.

Dzanis DA. Propylene glycol unsafe for use in cat foods. FDA Vet 9(1):1-3, 1994.

Cowell CS, Stout NP, Brinkmann MF, Moser EA, Crane SW. Making commercial pet foods (Ingredient myths and facts). In: Hand MS, Thatcher CD, Remillard RL, Roudebush P (eds). Small Animal Clinical Nutrition, 4th Edition. Topeka, KS: Mark Morris Institute, 2000; p. 141.

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