Food toxicity: When good food goes bad (Proceedings)


Foods, whether for human or animal consumption, are supposed to provide nutrients for maintenance of health; however, situations arise where the food may be source of the problem.

Foods, whether for human or animal consumption, are supposed to provide nutrients for maintenance of health; however, situations arise where the food may be source of the problem. This concern is shared by veterinarians as well as consumers. For example, here is a post on the Veterinary Information Network:

"As I see it the pet food industry has created a monster. Convenient, well marketed diets that likely are a factor in creating diseases.... and then a plethora of prescription diets aimed at managing said diseases. With pet food companies pouring tones of cash into marketing, subsidizing academic clinicians and lecturers and advertising and sometimes subsidizing heavily in clinical veterinary centers what will the future hold? It seems that some astute clinicians now doubt the nutritional composition of many of the popular, convenient, widely available diets and moving more towards diets similar in composition to what the ancestors of our domestic friends used to eat. What our carnivorous pet dogs and cats are supposed to eat. Is it even feasible that the major pet food manufacturers could release new diets that better mimic the natural food stuff or would this just serve to undermine the basis of all of their other diets?"

This is fueled even more in lay publications, such as the book "Food Pets Die For" or in web site blurbs such as:

"Despite the appealing blandishments of pet food advertisements with their claims of providing "complete and balanced nutrition," if you're not exceedingly circumspect, you may end up feeding your pet chicken heads, road kills, spoiled or moldy grains, cancerous material cut from slaughterhouse animals, tissue high in hormone or pesticide residues, and even shredded Styrofoam packaging, metal ID tags and minced flea collars. A growing number of veterinarians state that processed pet food (kibbles and canned food) is the main cause of illness and premature death in the modern dog and cat. In December 1995, the British Journal of Small Animal Practice published a paper contending that processed pet food suppresses the immune system and leads to liver, kidney, heart and other diseases. Dr. Kollath, of the Karolinska Hospital in Stockholm, headed a study done on animals. When young animals were fed cooked and processed foods they initially appeared to be healthy. However, as the animals reached adulthood, they began to age more quickly than normal and also developed chronic degenerative disease symptoms. A control group of animals raised on raw foods aged less quickly and were free of degenerative disease" (however, I could not find this study published in this journal or any other journal) and "Dr. Don E. Lundholm, D.V.M. - "We are seeing disease conditions in animals that we did not see years ago. Many of these may be traced to nutrition as the source..." (source:, accessed August 9, 2009)

With recent pet food recalls the sentiment of pet food toxicity is widespread. And this is not limited to pet products. The FDA web site ( lists recalls, market withdrawals, and safety alerts of which there were over 50 entries for the month of July 2009 alone.

There are basically 2 types of toxicities that can occur with pet foods, as with human foods: toxins and infectious agents. Additional adverse food reactions may occur due to immunological and non-immunological reactions, such as consumption of an incomplete or unbalanced food or immunological reaction to a food-borne allergen. Infectious agents that may cause toxic reactions include aflatoxins, salmonella, E. coli, clostridium, campylobacter, and toxoplasma, to name a few. Aflatoxicosis occurred approximately 5 years ago. There are different types of mycotoxins depending on the fungus or mold involved. Aflatoxin involved in the pet food recall was primarily hepatotoxic and often fatal; however, not all dogs exposed to aflatoxin develop disease. Potentially pathogenic and zoonotic bacteria have been identified in dog food including E coli O157:H7 (enterotoxigenic E coli), salmonella, Yersinia enterocolitica, Campylobacter, Clostridium, and Listeria. Additionally, parasites may be transmitted in food, especially uncooked food, such as echinococcus ,taenia, toxocara, toxoplasma, trichinella, and neospora. The CDC ( provides information on infectious disease related food problems (

Toxins may be inadvertently or intentionally added to a pet food or a pet may consume them independent of their diet.

Chocolate is a mixture of cocoa beans and cocoa butter. It contains theobromine and caffeine, which are both classified as methylxanthines. Unfortunately, dogs are sensitive to the effects of methylxanthines. Depending on the dose, methylxanthines can cause hyperactivity, increased heart rate, tremors, and potentially death. Other effects seen with chocolate overdose include vomiting, diarrhea, increased thirst, increased urination, and lethargy.

The amount of methylxanthines present in chocolate depends varies with the type. The general rule is the more bitter the chocolate, the more toxic it could be. In fact, unsweetened baking chocolate contains almost seven times more theobromine as milk chocolate while white chocolate (a combination of cocoa butter, sugar, butterfat, milk solids, and flavorings without cocoa beans) contains negligible amounts of methylxanthines.

The mechanism of action of methylxanthines is to competitively inhibit cellular adenosine receptors which results in CNS stimulation and tachycardia. Although, theobromine and caffeine have an LD50 of 100 to 200 mg/kg, signs can be seen well below this dose. Mild signs can be seen at doses over 20 mg/kg, moderate effects are seen over 40 mg/kg, and severe effects are seen at doses over 60 mg/kg. Early treatment, including decontamination procedures such as emesis and activated charcoal, cardiovascular monitoring, and supportive care, is extremely helpful with chocolate poisoning. In addition, fluid diuresis may help enhance elimination. Caffeine can be reabsorbed by the bladder wall which may result in extended times of clinical signs; therefore, the veterinary staff should take extra steps to keep the patient's bladder empty either through catherization or frequent walking.

Macadamia nuts may cause problems if ingested by dogs. According to a retrospective study, clinical signs commonly reported in dogs ingesting macadamia nuts include weakness, depression, vomiting, ataxia, tremors, and hyperthermia. The lowest dose reported to cause clinical effects is 2.4 g/kg. In most cases, dogs developed clinical signs within the first twelve hours post ingestion. These signs have only been seen in dogs and the exact cause for their sensitivity is unknown. Treatment includes decontamination procedures such as inducing emesis, administering activated charcoal, and administering enemas. Additional supportive care should be given as needed. The prognosis in most cases is extremely good. Most dogs return to normal within 24 to 48 hours.

Some types of grapes and raisins have been shown to cause kidney failure in dogs when eaten in quantity. The basis for kidney failure following consumption of grapes or raisins is unclear, but is currently being studied in the veterinary community. The amount of grapes or raisins that may cause renal failure is not exactly known, so any amount could potentially be dangerous. As for treatment of recent ingestion, inducing vomiting and administering activated charcoal is recommended. This should be followed with fluid diuresis for 48 hours. During this time the patient should be monitored for azotemia. If the animal shows evidence of renal failure, fluids and supportive care should be continued.

Xylitol is a naturally occurring sugar substitute. Use of xylitol has recently expanded in popularity, and xylitol is found in many sugar-free gums, candies, and other foods. Dogs appear sensitive to xylitol, as ingestion of 100mg/kg xylitol can result in rapid, life-threatening hypoglycemia (no known toxicity exists for humans). Doses exceeding 500-1000mg/kg have been associated with acute hepatic failure and coagulopathy. Treatment is directed at managing the hypoglycemia (dextrose infusions), coagulopathy (plasma transfusions), and supportive treatment for liver failure.

More recently, melamine-and cyanuric acid-induced renal failure and Fanconi syndrome associated with jerky treat ingestion have been in the news. How did this occur? Wheat gluten is a vegetable protein used to increase the nitrogen and protein content of a food. The crude protein analysis used for pet foods is based on analysis of the nitrogen in the ingredient or food multiplied by a factor (6.25). The amine group of melamine is analyzed as nitrogen; therefore, in adding melamine to the wheat gluten the measured nitrogen and thus the crude protein value is increased even though this is not bioavailable. Melamine alone is minimally toxic; however, when combined with cyanuric acid in acidic urine, crystal formation occurs that can result in renal failure. Despite quality control measures including supplier factors, certificate of analysis, truckside testing, line samples, and bag samples, contamination occurred resulting in hundreds and likely thousands of pets dying. In Fall 2006, a wheat gluten supply shortage occurred, and in December 2006 new suppliers were identified. In February 2007, cats undergoing a palatability trial at Iams died followed by Menu Foods recall in March 2007. By April 2007, melamine and cyanuric acid had been identified and incriminated as cause of crystalluria and renal failure. Although this seems like a long time for identification of a toxin in food, four months is quick. At that time, identification of a problem may have taken longer because multiple gluten manufacturers were involved, there was no central reporting agency, the toxins involved were unusual and difficult to detect, and because renal failure is a common condition. While the story unfolded in the news, within approximately a year, melamine was found to be present in infant formula with thousands being affected with kidney stones and death occurring. The story first broke in September 2008 and the manufacturer of the infant formula had received a complaint of illness in March 2008. The World Health Organization issued a report on melamine and cyanuric acid in October 2008 (

More recently, consumption of chicken jerky treats primarily, but not exclusively, sourced from China has been associated with Fanconi syndrome in dogs. The cause(s) has not been identified.

Recognizing food-associated illness can be difficult as often cases present sporadically with no apparent connection. Recognizing clusters of cases geographically (e.g. regionally) or during the same time period (e.g. animals in same household) is important. Take a good diet history from the owners. Introduction of a new food or a new bag of food, poor palatability or acceptance of the food by the pet(s), and pets eating the same food whether in the same household or different households may provide clues to problems with diet. Keep in mind that animals may present with similar clinical signs and histories but consuming different diets and/or snacks/treats. Discuss cases with your colleagues as they may be having similar experiences that can support your concerns.

Reporting potential adverse reactions

• Contact the manufacturer – they should be willing to listen and take information as well as answer questions as to whether other complaints have occurred

• FDA: – specifically

     o FDA: Pet Food site at gives information as to pet food news releases and information for consumers

     o FDA – report a problem:

• AVMA: – specifically, this link for reporting adverse events with drugs, vaccines, and pet food:

     o To report an adverse event associated with pet food (or other animal feed), please contact your state FDA's Consumer Complaint Coordinator(s). Contact information can be found on the FDA's Web site at When reporting, please include as much information as possible, including the specific product name, lot numbers, veterinarian's report and diagnosis, and any other pertinent information.

It is important to gather as much information as possible and to save as much as possible. Document the product name, type of food, manufacturer/distributer information, and date code/best buy code. Keep a copy of the packaging if you can. If the owner has a copy of the purchase receipt, it helps. Retain samples of the food; keep at least 4 cans or pouches of canned or semi-moist food and 1 kg of dry food. Do not send all of the samples for analysis – keep or have the owner keep some. Have the owner document consumption of the food by pet(s) with as much detail as they can recall. Keep good records including signalment, clinical signs, and test results. If a pet dies, perform a necropsy or have a necropsy performed. Make sure to tell the diagnostic lab performing the necropsy of your suspicion of toxicity. Save tissue and fluid samples, if possible. Document communication with the manufacturer and with FDA/AVMA. If other pets may have been exposed, test them.

Pet food toxicities occur commonly, but less so than in human beings. The CDC estimates that 76 million Americans get sick, more than 300,000 are hospitalized, and 5,000 people die from food borne illnesses each year. After eating contaminated food, people can develop anything from a short, mild illness, often mistakenly referred to as "food poisoning", to a life-threatening illness. Be suspicious of a food-related disease especially if you notice trends in households, food consumed, or clusters of cases geographically. Save food and information as described. Report immediately – "better to be safe than sorry". You are not being paranoid. Have owners discontinue feeding suspected food immediately. On a short-term, owners can home cook, if they wish. In order to minimize risk of food poisoning in pets

  • Do not allow them access to garbage or carrion

  • Cover and refrigerate unused portions of wet food

  • Do not feed foods that have a suspicious appearance or odor

  • Use stainless steel bowls and utensils and clean them

  • Store dry foods in a cool dry location free of pests

The Veterinary Information Network ( has an informational FAQ concerning homemade pet foods in a pet food crisis that was developed during the melamine-cyanuric acid recall ( In this FAQ, the following generic adult dog and cat food recipe is provided.

Generic recipe

This recipe should be fed for not more than 2 months. Clinicians are advised to set up a consultation with the client at the end of this period to revisit feeding requirements and to consider either re-instituting commercial food products, or a consultation with a clinical nutritionist.


The ACVN (

Angell Memorial :617 / 522 – 7282

Michigan State: 517 / 432 - 7782

Ohio State: 614 / 292 – 1221,

Tufts University: 08 / 839 – 5395 ext 84 696

UC Davis: 530 / 752 – 1387,

University of Missouri:

University of Tennessee: 865 / 974 – 838,7

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