ALBANY, N.Y. (AP) – Aminopterin has been used to induce abortions, treat cancer and kill rats. What it was doing in pet food is what owners of a rising number of sick or dead animals are demanding to know.

The drug was identified Friday as the likely culprit in a poisoning scare that prompted the recall of 95 brands of “cuts and gravy” style dog and cat food. Scientists had no theories on how aminopterin got into the products of Menu Foods, which makes pet food for most of North America’s top retailers.

Some pets that ate the food suffered kidney failure, and the company has confirmed the deaths of 15 cats and one dog.

Menu Foods expanded its recall Friday to cover each of the tens of millions of cans and pouches produced under the affected brands. The original recall covered only pet food produced from Dec. 3 to March 6.

“Before they put this stuff in the bags, there should be some kind of test,” said Jeff Kerner, whose Yorkshire terrier Pebbles died Thursday of kidney failure days after eating some of the food.

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.

Aminopterin is a cancer drug that once was used to induce abortions in the United States and is still used to kill rats in some other countries, state Agriculture Commissioner Patrick Hooker said.

Aminopterin 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.

Officials said there is no risk to pet owners from handling the food, but Donald Smith, dean of Cornell’s veterinary school, said he expected the number of pet deaths would increase.

The federal government prohibits using aminopterin for killing rodents in the U.S. State officials would not speculate on how the poison got into the pet food, but said no criminal investigations had been launched.

Stephen Sundlof, the U.S. Food and Drug Administration’s top veterinarian, said the agency hasn’t ruled out sabotage, but doesn’t have any leads – nor any theories how the drug could have contaminated the pet food.

The FDA believes the drug was used only in animal feed but has asked the Centers for Disease Control and Prevention to watch for any uptick in human cases of poisoning.

“This is very, very precautionary. We have no reason whatsoever to believe this chemical has entered the human food supply,” Sundlof told reporters.

The FDA has said the investigation into the pet deaths was focused on wheat gluten in the food, and Sundlof said it remains the suspected source of the contamination.

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

Andre Rosowsky, a chemist with the Dana Farber Cancer Institute in Boston, speculated that the drug would not show up in pet food “unless somebody put it there.” Aminopterin is no longer marketed as a cancer drug, but is still used in research, he said.

Menu Foods, already facing lawsuits, said Friday it is testing all the ingredients that go into the food.

“We have a lot of work to do, and we are eager to get back to it,” Henderson said. “This is a highly unusual substance.”

He said the company 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.

When asked whether there would compensation for medical bills for sick pets, Henderson said “to the extent that we identify that the cause of any expenses incurred are related to the food, Menu will take responsibility for that.”

Robin Godfrey of Weston, W. Va., said that was good news. She said her family can’t afford the $800 veterinary care would cost for their two mixed-breed dogs and six puppies, who fell sick after eating one of the recalled brands.

“If they should die, part of me would die with them,” Godfrey said.

Kerner, the owner of the Yorkshire terrier who died, said he was contacting an attorney, mostly in the interest of preventing another pet tragedy. He was repeatedly reminded of his loss on the Internet because of an Associated Press photo of Pebbles in a clinic, taken a day before she died.

“Although my family loves me, no one ever loved me like that dog,” Kerner, 48, of Sherman Oaks, Calif., said tearfully over the phone. “Every Web site I go to I see my dog. She was so cute.”

A complete list of the recalled products along with product codes, descriptions and production dates was posted online by Menu Foods and is available at http://tinyurl.com/2pn6mm. The company also designated two phone numbers that pet owners could call for information: (866) 463-6738 and (866) 895-2708.

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Associated Press writers Andrew Bridges in Washington, Michael Virtanen in Albany and Solvej Schou in Los Angeles contributed to this report.

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On the Net:

FDA pet food recall information: http://www.fda.gov/oc/opacom/hottopics/petfood.html

Menu Foods: http://tinyurl.com/2pn6mm

AP-ES-03-23-07 2007EDT