Nestle Purina PetCare Co. said it was recalling all sizes and varieties of its Alpo Prime Cuts in Gravy wet dog food with specific date codes. Purina said a limited amount of the food contained a contaminated wheat gluten from China. (Check the Purina Web site for details.)
The same U.S. supplier also provided wheat gluten, a protein source, to a Canadian company, Menu Foods, which this month recalled 60 million containers of wet dog and cat food it produces for sale under nearly 100 brand labels. (Check the Menu Foods Web site for details.)
Menu Foods and the Food and Drug Administration, which regulates the pet food industry, have refused to identify the company that supplied the contaminated wheat gluten.
Hill's Pet Nutrition said late Friday that its Prescription Diet m/d Feline dry cat food included the tainted wheat gluten. The FDA said the source was the same unidentified company. Hill's, a division of Colgate-Palmolive Co., is so far the only company to recall any dry pet food. (Check Hill's Pet Nutrition Web site for details.)
Federal testing of some recalled pet foods and the wheat gluten used in their production turned up the chemical melamine. Melamine is used to make kitchenware and other plastics. It is both a contaminant and byproduct of several pesticides, including cyromazine, according to the Environmental Protection Agency. Melamine is toxic only in very high doses and has been shown in rats to produce bladder tumors, according to the EPA.
Emergency vet Dr. Benjamin Davidson said finding melamine is not solid proof of what killed the pets.
"We know the compound is present, but there is no cause-and-effect relationship. We don't know that 'Yes, this is the compound that is definitely causing the renal disease,'" Davidson told CBS News correspondent Sharyn Alfonsi.
The federal pet food testing failed to confirm the presence of aminopterin, a cancer drug also used as rat poison, the FDA said. Cornell University scientists also found melamine in the urine of sick cats, as well as in the kidney of one cat that died after eating some of the recalled food.
Earlier, the New York State Food Laboratory identified aminopterin as the likely culprit in the pet food. But the FDA said it could not confirm that finding, nor have researchers at the University of Medicine and Dentistry of New Jersey when they looked at tissue samples taken from dead cats.
Experts at the University of Guelph in Canada detected aminopterin in some samples of the recalled pet food, but only in very small percentages.
"Biologically, that means nothing. It wouldn't do anything," said Grant Maxie, a veterinary pathologist at the university. "This is a puzzle."
The FDA was working to rule out the possibility that the contaminated wheat gluten could have made it into any human food.
Menu Foods announced the recall this month after animals died of kidney failure after eating the company's products.
An FDA official allowed that it was not immediately clear whether the melamine was the culprit. The agency's investigation continues, said Stephen F. Sundlof, director of the FDA's Center for Veterinary Medicine.
Menu Foods said the only certainty was that imported wheat gluten was the likely source of the deadly contamination, even if the actual contaminant remained in doubt.
"The important point today is that the source of the adulteration has been identified and removed from our system," said Paul Henderson, Menu Foods chief executive officer and president. Henderson suggested his company would pursue legal action against the supplier.
About 70 percent of the wheat gluten used in the United States for human and pet food is imported from the European Union and Asia, according to the Pet Food Institute, an industry group.
One veterinarian suggested the international sourcing of ingredients would force the U.S. "to come to grips with a reality we had not appreciated."
"When you change from getting an ingredient from the supplier down the road to a supplier from around the globe, maybe the methods and practices that were effective in one situation need to be changed," said Tony Buffington, a professor of veterinary clinical sciences at Ohio State University.
Sundlof said the agency may change how it regulates the pet food industry.
"In this case, we're going to have to look at this after the dust settles and determine if there is something from a regulatory standpoint that we could have done differently to prevent this incident from occurring," he said.