Updated

Salvaged pet food contaminated with an industrial chemical was fed to hogs in as many as six states, federal health officials said Tuesday. It was not immediately clear if any of the hogs entered the food supply for humans.

Food safety officials have quarantined hogs at farms in California, New York, North Carolina, South Carolina, Utah and possibly Ohio. The urine of hogs in some states has tested positive for the chemical, melamine, the Food and Drug Administration said.

"At this point, I don't have a definitive answer other than to say that the issue is being addressed," Stephen Sundlof, the FDA's chief veterinarian, told reporters when asked if any of the hogs had entered the food supply. A poultry farm also may be involved, he added.

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The FDA also said it planned to begin testing a wide variety of vegetable proteins at firms that imported the ingredients to make everything from pizza dough to infant formula, and protein shakes to energy bars. The ingredient list includes wheat gluten, corn gluten, corn meal, soy protein and rice bran.

Investigators have found melamine in at least two imported Chinese vegetable proteins used to make pet foods. The chemical likely was used to skew analyses that measured the protein content of the ingredients, wheat gluten and rice protein concentrate.