ALBANY, N.Y. -- Rat poison was found in the pet food suspected of causing kidney failure that killed at least 16 cats and dogs, but scientists still don’t know how it got there, state officials said Friday.

The toxin was identified as aminopterin, which is used to kill rats in some countries, state Agriculture Commissioner Patrick Hooker said.

Aminopterin is not registered for killing rodents in the United States, according to the Environmental Protection Agency, though it is used as a cancer drug. State officials wouldn’t speculate on how the toxin got into Menu Foods’ now-recalled pet food but said no criminal investigations had been launched.

Scientists at the New York State Animal Health Diagnostic Center at Cornell and at the New York State Food Laboratory tested three cat food samples provided by Menu Foods and found Aminopterin in two of them. Hooker said they would be testing individual components of the pet food, as well.

“Any amount of this product is too much in food,” he said.

Aminopterin, also used as a cancer drug, is highly toxic in high doses. It inhibits the growth of malignant cells and suppresses the immune system. In dogs and cats, it can cause kidney failure, according to Donald Smith, dean of Cornell University’s College of Veterinary Medicine.

AP

Pebbles, a 7-year-old Yorkshire terrier, is battling kidney failure after eating dog food that was later recalled.

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

The pet deaths led to a recall of 60 million cans and pouches of pet food produced by Menu Foods and sold throughout North America under 95 brand names. There have been several reports of kidney failure in pets that ate the recalled brands, and the company has confirmed the deaths of 15 cats and one dog.

Menu Foods last week recalled “cuts and gravy” style dog and cat food. The recall sparked concern among pet owners across North America. It includes food sold under store brands carried by Wal-Mart, Kroger, Safeway and other large retailers, as well as private labels such as Iams, Nutro and Eukanuba.

The company’s chief executive and president said Menu Foods delayed announcing the recall until it could confirm that the animals had eaten its product before dying. Two earlier complaints from consumers whose cats had died involved animals that lived outside or had access to a garage, which left open the possibility they had been poisoned by something other than contaminated food, he said.

Menu Foods planned a media teleconference for later Friday, a spokesman said. The company is majority owned by Menu Foods Income Fund of Streetsville. The company also makes foods for zoo cats, but those products are unaffected by the recall.

A spokesman for New York Attorney General Andrew Cuomo said he was not aware of any criminal investigation involving the tainted food. FBI spokesman Paul Holstein in Albany said Friday he was not aware of any FBI involvement in the case.

“I don’t know where we’ll go from here,” he said.

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.

New York State is home to two laboratories that are part of federal emergency lab networks, created after the Sept. 11 terrorist attacks to keep the nation’s animals and food supply safe.

The New York State Food Laboratory is part of the Federal Food Emergency Response Network and is capable of running a number of toxin tests on food, including the test that identified aminopterin.