The government said the risk to humans is very low from hogs that may have eaten contaminated pet food.
The Food and Drug Administration and the Agriculture Department said their ongoing investigation has also determined that no hog recall is needed.
Several hundred hogs that ate the food contaminated with melamine are believed to have been placed on the path to slaughter, but thousands more are still on farms in California, New York and South Carolina.
Those states have been told no meat from any of those hogs can enter the food supply.
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