Pet Owners Double Checking Cabinets

Pebbles, the Yorkshire terrier that became a symbol of the national pet food scare is shown in this, March 21, 2007 file photo, at Collett Veterinary Clinic in Los Angeles. Pebbles died Thursday while being treated for kidney failure that developed after she ate some of the suspect food. (AP Photo/Reed Saxon, file) (Reed Saxon - AP)

The Food and Drug Administration has said the investigation into the pet deaths was focused on wheat gluten in the food. The gluten itself would not cause kidney failure, but it could have been contaminated, the FDA said.

Paul Henderson, chief executive of Menu Foods, confirmed Friday that the wheat gluten was purchased from China.

Bob Rosenberg, senior vice president of government affairs for the National Pest Management Association, said it would be unusual for the wheat to be tainted.

"It would make no sense to spray a crop itself with rodenticide," Rosenberg said, adding that grain shippers typically put bait stations around the perimeter of their storage facilities.

Scientists at the New York State Animal Health Diagnostic Center at Cornell University and at the New York State Food Laboratory tested three cat food samples provided by the manufacturer and found aminopterin in two of them. The two labs are part of a network created after the Sept. 11 terrorist attacks to keep the nation's animals and food supply safe.

"Any amount of this product is too much in food," Hooker said.

Aminopterin is highly toxic in high doses. It inhibits the growth of malignant cells and suppresses the immune system. In dogs and cats, the amount of aminopterin found _ 40 parts per million _ can cause kidney failure, according to Bruce Akey, director of Cornell's diagnostic center.

"It's there in substantial amounts," Akey said.

Donald Smith, dean of Cornell's veterinary school, said he expected the number of pet deaths to increase. "Based on what we've heard the last couple days, 16 is a low number," Smith said.

Aminopterin is no longer marketed as a cancer drug, but is still used in research, said Andre Rosowsky, a chemist with the Dana Farber Cancer Institute in Boston.

Rosowsky speculated that the substance would not show up in pet food "unless somebody put it there."

Henderson said Menu Foods does not believe the food was tampered with because the recalled food came from two different plants, one in Kansas, one in New Jersey. Menu continues to produce food at the two plants.