Pet Food Contaminants

As part of my duties as an AAFCO advisor and member of several Working Groups, I attend numerous webinars and teleconferences. In one group, the discussion centered around the use of 4D meats and other rotten junk in pet food, and the consensus was that as long as these things are rendered (heat-processed) to kill pathogens, they’re perfectly fine for pet food. Well, that just isn’t true. So I put together the following document to show that there are MANY potential toxic principles in pet food that need to be considered. I prepared the following paper to prove it; and am sharing it with you. Please feel free to share it, as you do not make any changes, and you include proper attribution and a link back to

There is to more awareness growing among pet parents, and a new readiness to hear the truth. People are less naïve about the advertising hype constantly spewing from the marketing departments of pet food companies, and this bothers pet food manufacturers—a lot! We’re seeing more and more stretching of the truth, as these companies become more desperate to fool more of the people, more of the time!

Now, your pet food consumer advocates—Susan Thixton of, Mollie Morrissette of, and I (Dr. Jean Hofve of—have already been providing that education for many years. After all, here you are reading it!

After many hours spent in many meetings with representatives from AAFCO, FDA, and other regulatory bodies, we’ve basically been told that our best course to improve the situation is to educate consumers… without any support from them. Certainly, the industry isn’t going to do it!

So here are the reasons why just cooking “the bad” out of pet food ingredients DOES NOT MAKE THEM SAFE FOR YOUR PET TO EAT. 

A Report to the AAFCO Pet Food Committee Working Group

Potential Contaminants of Pet Food

Jean Hofve, DVM

November 2015

  1. Bacterial Endotoxins

While the rendering process kills bacteria, it does not eliminate the endotoxins or spores that some of those organisms produce. These contaminants can survive processing and cause sickness and disease.

Toxin-producing bacteria like Salmonella, E. coli, Clostridia, Staph, and other gram-negative bacteria are very common contaminants of all slaughterhouse products (including human-edible meat and poultry), but especially of the sorts of things that make up by-products, such as digestive organs. [Strombeck 2010, Cullor 2001]

When infected animals die, massive numbers of bacteria from the colon migrate out and contaminate the carcass. Rendering kills bacteria, but also releases large amounts of endotoxin. Unlike bacteria, endotoxins are not altered by processing. Even a small amount of endotoxin present in the finished product can make pets sick.

Despite rendering, live coliforms have been cultured from rendered meat meal. [Strombeck 2010] 

Even when high temperatures during rendering and extrusion kill all the bacteria, the final product loses its sterility during drying, spray-coating, and packaging processes. In one survey, live bacteria were cultured from the surface of every single one of 50+ dry dog and cat foods tested. [Cullor 1999-2000]

The usual number of bacteria in most animal products used for food is 1,000 to 10,000 per gram. In one study, 40 mg of endotoxin was given orally to normal pigs and goats. They all showed signs of illness, some severe. [Cort 1990] The pig’s digestive system is very similar to that of dogs and cats.

“Small amounts of endotoxin cause shock that can lead to death… Endotoxin can initiate and perpetuate damage to the intestinal mucosal surface, and it can perpetuate inflammatory diseases of the digestive system, including allergies.” [Strombeck 2010]

2. Bacterial Spores

Certain types of bacteria, including food-borne strains like Clostridia and Bacillus, produce spores as part of their reproductive process. These spores are extremely resistant to pasteurization, boiling, freezing, acid, and high heat. They can survive the processing that pet food undergoes, including rendering. [Andersson 1995, Franke-Whittle 2013] 

Bacillus cereus is particularly troubling because research demonstrated that it could be cultured from every one of more than 50 sampled dry dog foods. [Cullor 1999] B. cereus is a very common contaminant of a wide array of foods; it causes vomiting and diarrhea when ingested. It is likely that many cases of gastrointestinal illness in pets with no known cause (so-called “garbage gut”) are actually due to B. cereus contamination of pet food.

3. Antibiotic Resistant Organisms

Food animals can become hosts to antibiotic resistant bacteria through either contaminated feed or administration of subtherapeutic antibiotics to the animal. Carcass contamination during slaughter is a common route for human infection. While bacteria are killed during most pet food processing methods, fragments of bacteria or bacterial DNA can pass the resistant trait to resident organisms in a pet’s digestive tract that can potentially be transmitted to humans and other animals through fecal contamination of the environment. [Davis 2003]

One study found multi-drug resistant Enterococci and methicillin-resistant Staphylococcus aureus from dog fecal samples collected from city streets and sidewalks. The presence of the resistant bacteria in an urban environment may represent a public health hazard which requires control measures by competent authorities. [Cinquepalmi 2013]

4. Fungal Toxins

Some types of mold produce toxins similar to bacterial endotoxins. Modern farming practices, adverse weather conditions, and improper drying and storage of crops can contribute to mold growth. Aflatoxin, ochratoxin, fumonisin, trichothecene, zearalenone and patulin are the most common mycotoxins in animal feed (and human food).

When mycotoxins are present in feed consumed by livestock, they can contaminate meat and milk from those animals. [Boudra 2007; Milićević 2010; Peska 1995] This is significant because even if a manufacturer tests grain products for aflatoxin, it may completely miss significant levels in animal-source ingredients.

Many mycotoxins are toxic; even low concentrations can cause autoimmune disease, including allergies. Others are teratogenic, carcinogenic, and mutagenic [Bennet 2003; CAST 2003]. Mycotoxins are relatively heat-stable; some can withstand temperatures up to 300oF. Very little if any destruction occurs under normal food processing conditions and temperatures. [Milićević 2010]

Mycotoxins can have both acute and chronic effects on animals, especially monogastric (one stomach) animals, including dogs, cats, and humans. [Hussein 2001; Milićević 2010; Zain 2011]. The effects of mycotoxins in food include loss of human and animal life, and increased health care and veterinary care costs. [Hussein 2001]

The pet food ingredients most likely to be contaminated with mycotoxins are grains such as wheat and corn; as well as fishmeal. However, virtually any food can be contaminated. There have been many large recalls of pet food in response to illness and death in pets due to one very powerful poison—aflatoxin—in dry food. Survivors may continue to experience problems, as aflatoxin is highly carcinogenic and can cause disease even at low levels of exposure; it is also genotoxic. [Buss 1990; Milićević 2010] Ochratoxin affects primarily the kidneys. Trichothecenes cause vomiting, diarrhea and bowel inflammation; they are also immunosuppressive. Fumonsins are “ubiquitous in corn” and are particularly toxic to the nervous system. [Milićević 2010]

5. Pharmaceutical drugs

Because sick or dead animals are frequently processed for pet foods, the drugs that were used to treat or euthanize them may still be present in the end product: the pet food you bring into your kitchen. Penicillin and pentobarbital are just two examples of drugs that can pass through processing unchanged. [Markus 1989; FDA/CVM 2002] There are a few kidney-toxic antibiotics that are extremely restricted, with long “withdrawal” times before slaughter for human food; but if livestock die with high levels of drugs in their systems, they are condemned for human consumption but can still be rendered and used in pet food.

It has been known for many years that overuse of antibiotics in livestock are a factor in multi-drug resistance and human illness.

“Recycling animal waste into animal feed has been practiced for > 40 years as a means of cutting feed costs… [AAFCO] advises that processed animal waste should not contain pathogenic microorganisms, pesticide residues, or drug residues that could harm animals or eventually be detected in animal-based food products intended for human consumption. Nonetheless, these guidelines are not adequately enforced at the federal or state level.” [Sapkota 2007]

If antibiotic-treated animals are not segregated, then their drug-loaded wastes will likely be included in rendered products and pet food.

6. Chemical Contaminants and Residues 

Pesticides and fertilizers may leave residue on plant products. [Grisamore 1991] Grains that are condemned for human consumption by the USDA due to excessive residues may legally be used in pet food. (FDA Compliance Policy CPG Sec. 675; USDA personal communication 2001)

Dioxins, PCBs, fire retardants, and other persistent organic pollutants may be present in animal tissues used in both human food and animal feed, including pet food. [Fernández-González 2015; Srogi 2007] Other chemicals found in food include insecticides, rodenticides, fluoroquinolone antibiotics, bovine somatatropin, radioactive waste, and many more. Endocrine disruptors such as bisphenol-A are present in foods as well as some types of packaging, including steel and aluminum cans. Chemicals, as opposed to microbes, are typically thermally stable and not affected by heat from processes like rendering and extrusion. [Mansour 2011]

One toxic herbicide that is NOT on the USDA’s radar is glyphosate (Monsanto’s Roundup©). They do not test for it, so there is no limit to the amount of this toxin that can be present in the food that we eat, let alone pet food.

7. Maillard Reaction Products/Advanced Glycation End Products (AGEs)

This broad group of chemicals includes the known carcinogen acrylamide, as well as many other potentially toxic compounds. They form at cooking temperatures of about 250˚F in foods containing certain sugars and proteins, particularly the amino acid asparagine (found in large amounts in potatoes and cereal grains) due to a chemical process called the Maillard reaction. This reaction reduces protein bioavailability, so that no matter what the guaranteed analysis says about protein levels, the amount a pet can use is significantly less. Most dry pet foods contain cereal grains or starchy vegetables such as potatoes, as well as animal proteins, and they are processed at high temperatures (200–300°F) at high pressure during extrusion; baked pet foods are cooked at 500°F or more. These conditions are perfect for this reaction to occur. In fact, the Maillard reaction is considered desirable in pet food because it imparts a palatable taste, even though it reduces the bioavailability of taurine, lysine, and other amino acids. The amount and effects of acrylamide in pet foods are unknown; but research shows that other Maillard reaction products are present in pet foods in much higher amounts than in human food. [van Rooijen 2014] Current research is finding that a combination of more heat processing and less moisture dramatically increases AGE levels in pet food. [Conway 2016]

8. GMOs

Genetically engineered or modified plant products are also of concern. Currently, 95% of U.S.-grown soybeans and corn are GMO. Soy and corn are very common pet food ingredients; and they are also fed to most U.S. livestock and poultry. This creates a sort of double whammy; since the products of genetically altered DNA may be present in the animal products used in pet food, as well as being fed directly to our pets. A 2009 study found significant damage to the liver and kidneys of rats fed genetically modified corn [de Vendômois 2009].

Even if GMOs themselves are ultimately found to be safe, their use has resulted in a huge increase in herbicide application to crops, since weeds have adapted themselves to thrive despite it. Herbicides can be very toxic. For example, the active ingredient in Monsanto’s Roundup®, glyphosate, inhibits liver and endocrine functions, which in turn have widespread effects all over the body. [Claire 2012, Samsel 2013]. Because glyphosate is toxic to bacteria, it also has deleterious effects on mammals’ all-important commensal gut bacteria. If a plant product contains excessive herbicide residue, it is rejected for human consumption and may be diverted to animal feed, including pet food. 

8. Heavy Metals and other Toxins

A study was conducted to assess the content of 15 toxic elements in pet food; samples were taken of wet and dry dog and cat foods across a range of prices. All tested foods contained toxic heavy metals; but the highest levels were found in dry foods. Toxic elements included arsenic, beryllium, cadmium, cesium, chromium, antimony, lead, molybdenum, nickel, thorium, thallium, uranium, and vanadium. The researchers compared the amount of these toxins in the food to allowable limits in human food, and found that the dose that would be consumed by the average pet exceeded limits set by the U.S. Environmental Protection Agency (EPA) and the World Health Organization (WHO) for most of the foods [Atkins 2011]. The FDA later disputed these findings [FDA 2011], but their arguments are based primarily on “maximum tolerable levels,” which is not equivalent to “safe for long-term consumption by pets in every meal of every day”—a standard that pet guardians rightly expect. [Fries 2014]

FDA itself recently conducted tests to ascertain current levels of arsenic in poultry. They found that the levels were higher than expected, especially in chicken livers. [FDA 2015] While the last of the arsenic-containing drugs will supposedly be withdrawn by the end of this year, pet food being made now, pet foods containing poultry liver or by-products that are currently on the market may contain significant levels of arsenic. Such foods will continue to constitute a threat to pet health until 2017, based on an expected 12- to 18-month shelf life.

Dioxins, PBDEs, and PCBs may also be present in animal tissues; one study found levels of these toxins in the US that were 3-20 times higher than Asia or Europe. [Fernández-González 2015]


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