The Food and Drug Administration advised pet owners today that recalled pet food may still be on the shelves in some retail establishments. The agency asked retailers across the country to be vigilant in removing all products associated with the pet food recall, which began on March 16.

Stephen Sundlof, director of the agency's Center for Veterinary Medicine, told lawmakers during a hearing that thousands of government and private sector workers around the country have responded to the contamination. Yet, he told lawmakers that he could not rule out the discovery of more tainted food.

"We do believe we've got the vast, vast majority off the market," Sundlof told members of a Senate Appropriations subcommittee.

On March 16, Menu Foods recalled 60 million cans of dog and cat food after the deaths of 16 pets, mostly cats, that ate its products. The FDA said tests indicated the food was contaminated with an industrial chemical.

At least six pet food companies have recalled products made with imported Chinese wheat gluten tainted with the chemical. The recall involved about 1 percent of the U.S. pet food supply.

Sen. Dick Durbin, D-Ill., said the contamination showed that pet food as well as human food is at risk because of significant gaps in the system of regulations and inspections that governs the food industry. In particular, he said, the latest contamination shows that not enough manufacturers of pet food are being inspected.