The government yesterday moved to block the slaughter and processing of 6,000 hogs as food because the animals ate food contaminated with melamine.

The move, announced by officials of the U.S. Department of Agriculture and U.S. Food and Drug Administration, involves hogs on farms in seven states.

The government plans to compensate farmers for the animals, but U.S. officials yesterday couldn't put a dollar figure on the cost.

Dr. Stephen Sundlof, director of the FDA's Center for Veterinary Medicine, has said melamine is a chemical used primarily to make plastic kitchenware, although it has been used as a fertilizer in Asia.

"It's our expectation that the best course of action" would be to "humanely euthanize" all of the animals on the farms where they are being raised, said Dr. Kenneth Peterson, assistant administrator for field operations in the USDA's Food Safety and Inspection Service. Federal and state officials will supervise the process to make sure that the animals are disposed of properly and do not end up in the food chain.

The 6,000 hogs live on eight farms in seven states: California, North Carolina, South Carolina, New York, Utah, Kansas and Oklahoma.

On Tuesday, FDA officials had said five states were involved. Yesterday, they added farms in Kansas and Oklahoma. They had been investigating hog operations in Ohio, but yesterday said facilities inspected there had not used contaminated feed. A chicken farm in Missouri is still being investigated, officials said at yesterday's news conference.

The USDA and FDA are working together "to find the farms where animals consumed the feed" that is contaminated, the USDA's Dr. Peterson said. He said his agency was also still investigating whether any hogs that ate contaminated feed may have already become pork products, even though federal officials have been saying they don't think that melamine-tainted wheat gluten or other tainted proteins have entered the nation's human food supply.

Dr. David Acheson, chief medical officer of FDA's Center for Food Safety and Applied Nutrtition, said officials "believe the risk" from melamine "to be extremely low to humans," but he also said melamine has only been tested on rats and other animals, never on humans.

In other announcements related to the pet food recall that began March 16, FDA officials announced that more companies and products added to the recall list. Drs. Foster & Smith Adult Dry Lite Dog Food and Adult Dry Cat Food have been voluntarily recalled by the manufacturer because the products could contain rice protein concentrate tainted with melamine. Chenango Valley Pet Foods is also recalling pet foods manufactured that contain rice protein concentrate.

Information about the recalled products, including production dates and codes, are available at www.fda.gov.