Del Monte Pet Products has become the latest company to voluntarily recall some of its brands. They include Jerky Treats Beef Flavor Dog Snacks and Pounce Meaty Morsels Moist Chicken Flavor Cat Treats.

Menu Foods recalled 60 million containers of cat and dog food in recent weeks after animals died of kidney failure after eating the Canadian company's products.

Menu Foods has confirmed the deaths of 15 cats and one dog. Some anecdotal figures suggest that many more may have died.

A greater sensitivity of cats to a chemical found in plastics and pesticides could explain why they've died in larger numbers than have dogs after eating contaminated pet food, experts said Saturday.

The small number of confirmed reports of pet deaths bolstered by a far larger number of unconfirmed anecdotal reports suggests cats were more susceptible to poisoning by the chemical melamine that tainted the now recalled pet food, officials with the Food and Drug Administration and American Society for the Prevention of Cruelty to Animals said Saturday.

"I am concerned we have a situation where we have a sensitive species and it is the cat," said Steven Hansen, a veterinary toxicologist and director of the ASPCA's Animal Poison Control center in Urbana, Ill.

Testing by the FDA and Cornell University has found melamine in samples of recalled pet food as well as in crystal form in the urine and kidney tissue of dead cats. They've also found the chemical, in apparently raw form in concentrations as high as 6.6 percent, in wheat gluten used as ingredient of the recalled cat and dog foods, said Stephen Sundlof, the FDA's chief veterinarian.

"There was a sizable amount of melamine. You could see crystals in the wheat gluten," Sundlof told The Associated Press.

Sundlof and others have not been able to explain why the chemical would have caused the kidney failure seen so far in the roughly 16 confirmed pet deaths, all but one in cats. There are anecdotal reports of hundreds more pet deaths.

"It has a very low toxicity, at least in rodents. The problem is, we don't have information in cats, and that seems to be the most susceptible species," Sundlof said of melamine. Sundlof also allowed that the tainted cat foods could have contained higher concentrations of melamine than did the dog foods.

Earlier this month, Menu Foods became the first of three pet food manufacturers to recall its products. It did so after cats began to fall sick and die during routine company taste tests of its wet-style pet foods, sold under nearly 100 store- and major-label brands across North America. Other than in the recalled products, melamine has not been found in other Menu Foods pet foods, the company said.

Melamine is used to make plastic kitchenware, glues, countertops, fabrics, fertilizers and flame retardants. It also is both a contaminant and byproduct of several pesticides, including cyromazine, according to the Environmental Protection Agency.

The United Nations Environment Program considers melamine of low potential risk, as does the EPA. The agency has sent FDA the database information it has on the chemical and will provide technical assistance as needed, EPA spokeswoman Enesta Jones said Saturday.

Sundlof said the FDA hadn't found any studies of melamine in cats, and the results of only a single 1945 study that tested it on dogs. That study suggested the chemical increased urine output when fed to dogs in large amounts.

"That was pretty much it," Sundlof said.

Still, it's well known that identical substances can have very different effects on cats and dogs. For example, the flea killer permethrin is OK to use on dogs but lethal to cats, Hansen said. The same could be the case with melamine.

"Cats are very sensitive to many different chemicals, whether drugs, pesticides or plants. We certainly know they have some unique physiological responses that make them susceptible in cases where we wouldn't expect it in other species," Hansen said.

The investigation has traced the melamine to wheat gluten that Menu Foods, Nestle Purina PetCare Co. and Hill's Pet Nutrition bought from an unnamed U.S. supplier. The latter two companies have recalled a limited number of products since Friday. The wheat gluten, a protein source, was imported from China.

Sundlof said the recall could expand further, depending whether other pet food manufacturers also bought wheat gluten from the same supplier.

"We're still in the process of tracing it at this point," Sundlof said. There is no indication the wheat gluten entered the human food supply, he added.

Salmonella Recall

Meanwhile, Eight in One is recalling packages of its Dingo brand dog, cat and ferret treats because of concerns over salmonella. The company says the bacteria could infect both animals and people handling the food.

Monday's announcement is not related to the recalls of tainted food that has led to kidney failure in pets around the country.

The recall involves Dingo Chick'n Jerky, Dingo Kitty Chicken Jerky and Dingo Ferret Chicken Jerky.

The company asks consumers to throw away unused portions of the jerky treats. To obtain a refund, call 888-232-9889.

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Del Monte Pet Products

Nestle Purina PetCare Co

Hill's Pet Nutrition

Menu Foods Recall Information -- menufoods.com/recall