March 23, 2007  -- The president of pet food maker Menu Foods, which last week issued a recall of 60 million cans and pouches of pet food after a rash of animal sickness and death, said today that the company would reimburse pet owners who can trace their pets' illnesses to the company's products.

Earlier today, New York State veterinary health investigators announced that the pet food responsible for pet deaths around the country was contaminated with the rodent poison aminopterin.

"A pet is an important part of any family," Paul Henderson, the president and CEO of Menu Foods, said at a Toronto press conference. "We understand what pet ownership is."

While Henderson described himself as "angry" over the massive recall and the impact it has had on hundreds of pets, he also said the company has not stopped manufacturing at the two plants believed to have produced the contaminated pet food.

Instead, he said the company, which manufactures nearly 100 brands of dog and cat food, will immediately begin testing any "suspect raw materials" to identify any additional contaminated products.

"We have the support of our customers, we have the support of our employees," Henderson said. "We're confident in the future and we remain confident we can put this behind us."

Investigators, meanwhile, are looking into whether the rat poison came into the United States on an ingredient used in the recalled food. ABC News has learned that Menu Foods bought wheat gluten, the only ingredient changed in its plants, from China. That possibility raises questions about the safety of pet and other food products in the United States.

The chemical can cause kidney failure in dogs and cats, said Donald Smith, dean of Cornell University's College of Veterinary Medicine, during the conference.

Scientists at the state's food laboratory in Albany, N.Y., made the discovery a week after Menu Foods issued its recall.

"This is one step in a long process that will lead us to know what has happened and how it has happened," Smith said.

Aminopterin is not registered for use as a pesticide in the United States, and it has been known as a potential source of birth defects in humans.

Interestingly, trials are under way to test the chemical's effectiveness in the treatment of certain types of cancer.

ABC News first reported that the rodenticide may have been present in the wheat that was imported from China and used by Menu Foods, according to a source close to the investigation.

Some Vets Remain Skeptical

Some veterinary experts say they are still skeptical as to whether the chemical is responsible for the kidney damage the pets endured.

"With the information that we have, none of us feel that this product fits the lesions we are seeing, but there may be information we don't know yet," said Lawrence McGill, a veterinary pathologist in Salt Lake City. "The feeling is that there are more questions than answers with this product."

"Renal failure is not the expected response to these drugs," said Susan Weinstein, executive director of the Massachusetts Veterinary Medical Association. She added that most rodent poisons work as severe anticoagulants -- meaning they cause the rats that ingest them to bleed to death.

"Whether this particular toxin in this case can create renal failure depends on how this drug works in the body, which may be an entirely different pathway than the anticoagulants," Weinstein said. "Because we aren't yet familiar with this toxin, we can't be confident of the causation link."

Investigators also have not yet determined whether aminopterin is the only contaminant in all the recalled food.

"If it is not the only culprit, as I suspect, the problem isn't over," McGill said, adding that it is also uncertain as to whether the finding will be much help to veterinarians.

According to McGill, even if the aminopterin is the culprit, "most veterinarians have never heard of this product. There will need to be more information put out to suggest therapeutic regimens."

Concerns May Spur Regulatory Response

With the widespread notoriety of the deaths associated with the contaminated pet food, some are beginning to speculate whether the result could be greater regulation of pet food safety.

"Certainly, finding something like this would have everyone step back and say, 'How do we make sure this never happens again?'" said Sandy Wellis, communications chair of the American College of Veterinary Internal Medicine.

"Knowing our public, they would probably like more regulation, and it may occur, but it hasn't happened with previous situations like this," McGill said. "There is a call for it, but will the public pay for it because it will make pet food more expensive."