Last spring, North America was gripped in the largest pet food recall in history. News outlets reported tens of thousands of dogs and cats becoming ill, and many dying, as a result of ingesting contaminated pet food. Several pet owners have filed lawsuits against the manufacturers and distributors of the pet food products. I think this is an excellent real-life science story to use with students to show science investigation in action, and to discuss the intersections between the role of regulatory agencies and the public.

In order to understand the case, you first have to know the facts. We'll begin with a timeline; unless otherwise noted, all dates occurred in 2007. Below each significant date are questions that can be explored with students.

Timeline and questions for discussion

February 20--Menu Foods Inc., the manufacturer of 95 top brands of pet food, first notices that some of their cats participating in taste testing become ill; nine cats subsequently died. Fourteen additional pet deaths are later reported to the company; renal (kidney) failure appears to be the cause of death in all of these cases. Menu Foods conducts an investigation to determine the link between the food and renal failure and contacts outside laboratories for assistance, but they do not notify the U.S. Food and Drug Administration (FDA) at this time.

Questions: What could be the link between the food and kidney failure? Why are only a few of the pets--compared to the likely hundreds of thousands that consume the food--becoming sick?

March 15--Menu Foods notifies the FDA of the problem, still with an unknown cause.

Question: Given the small number of cases reported by this date, do you think the company is justified in not reporting their findings to the public at this time?

March 16--Menu Foods initiates a voluntary recall of 60 million cans and pouches of dog and cat foods produced in Kansas and New Jersey between December 3, 2006, and March 6, 2007. At this time, the affected products are all wet, rather than dry, pet foods. Pet owners are told to dispose of any foods on the recall list, and to look for symptoms of illness or renal failure in their pets and seek medical treatment immediately if they arise.

Questions: Why are only wet foods, rather than dry, being affected? The recall that Menu Foods issues is voluntary--do you think the FDA should have required Menu Foods to issue a mandatory recall?

March 23--Aminopterin, a chemical component in rat poison, is announced as a possible cause of the pets' illnesses by a New York State agency. This finding is never confirmed in laboratory tests by the FDA and other labs, and is subsequently dismissed as the cause.

Question: What are some possible explanations for why one laboratory can come to a conclusion that aminopterin was contaminating the food, when no other laboratories reached that same conclusion?

March 30--Cornell College of Veterinary Medicine and the FDA announce that melamine, a chemical found in pesticides and plastics, was found as a contaminant in wheat gluten in the pet food. Additional pet-food companies voluntarily recall foods and treats containing wheat gluten as a precautionary measure. Melamine ingestion does not normally cause renal failure in dogs and cats, and scientists continue to investigate why the effects of melamine ingestion in these cases are so severe.

Also on March 30, the FDA confirms the melamine-contaminated wheat gluten was supplied by a Chinese company, and that this company provided analysis documents to the pet-food manufacturers stating that the wheat gluten was safe--however, the presence of melamine is not normally tested for in pet foods. A second Chinese company is later named as an additional supplier.

Questions: Why would melamine, which is normally not fatal if ingested, cause such a serious reaction in these pets? If the Chinese company provided documents that were found to be untrue, to what extent are the pet-food manufacturers to blame for these pet illnesses and deaths? …