Washington, D.C. ? As many as one in six animals died in tests of suspect dog and cat food by the manufacturer after complaints the products were poisoning pets across the country, the government said Monday.

A federal investigation is focusing on wheat gluten as the likely source of contamination that sparked a recall Friday of 60 million cans and pouches of the suspect food, said Stephen F. Sundlof, the Food and Drug Administration’s top veterinarian.

The ingredient, a protein source, commonly is used as filler.

Agency investigators are looking at other ingredients as well. The wet-style pet food was made by Menu Foods, an Ontario, Canada-based company.

Menu Foods told the FDA it received the first complaints of kidney failure and deaths among cats and dogs from pet owners on Feb. 20. It began new tests on Feb. 27.

During those tests, the company fed its product to 40 to 50 dogs and cats and seven animals died, Sundlof said. The contamination appeared more deadly to cats than to dogs, he said.

The recall now covers dog food sold throughout North America under 51 brands and cat food sold under 40 brands, including Iams, Nutro and Eukanuba. The food was sold under both store and major brand labels at Wal-Mart, Kroger, Safeway and other large retailers.