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WASHINGTON - Several hundred of the 6,000 hogs that may have eaten contaminated pet food are believed to have entered the food supply for humans, the government said Thursday. The potential risk to human health was said to be very low.

The government told the three states involved it would not allow meat from any of the hogs that ate the feed to enter the food supply.

No more than 345 hogs from farms in California, New York and South Carolina are involved, according to the Agriculture Department. It appears the large majority of the hogs that may have been exposed are still on the farms where they are being raised, spokeswoman Nicol Andrews said.

Salvaged pet food from companies known or suspected of using a tainted ingredient was shipped to hog farms in seven states for use as feed.

The government will compensate farmers if they kill those hogs, said Kenneth Peterson of department's Food Safety and Inspection Service. The department knew of no countries moving to suspend imports of U.S. pork products.

Also, a poultry feed mill in an eighth state, Missouri, also received possibly contaminated pet food scraps left over from production. The fate of the feed made from that waste was under investigation.

The pet food sent to the farms later was discovered to have an ingredient, rice protein concentrate, imported from China that was tainted by an industrial chemical, melamine. Testing also revealed other related and similarly banned compounds, including cyanuric acid. Food and Drug Administration inspectors were preparing to visit China as part of the agency's investigation.

Melamine is not considered a human health concern. But there is no scientific data on the health effects of melamine combined with the other compounds, said David Elder, director of enforcement for the FDA.

Still, the FDA and Agriculture Department believe the likelihood of someone becoming ill after eating pork from hogs fed contaminated feed is very low. Meanwhile, the University of California, Davis, is developing a test to measure melamine levels in tissue, Andrews said.

Since mid-March, pet food companies have recalled more than 100 brands of dog and cat food and treats; more recalls were announced Thursday. An unknown number of cats and dogs have fallen ill or died after eating products made with contaminated rice protein concentrate or a second tainted ingredient, wheat gluten.

Some pet food, while unsuitable for sale for that purpose, was still considered safe for animals to eat as it had not been recalled at the time it was forwarded to hog farms. Its use at hog farms raised the possibility that melamine entered the human food supply.

The department on Thursday released the following state-by-state breakdown of its investigation into farms thought to have received the contaminated pet food for use as hog feed. The farms were not identified.

• CALIFORNIA: State officials are working to contact the purchasers of 50 whole hogs raised on a single farm.
• NEW YORK: A breeder farm's 125 to 140 swine are under quarantine pending the results of urine and manure tests. None of the hogs went to slaughter.
• SOUTH CAROLINA: Urine tests done on some of the 800 hogs now quarantined at a farm have tested positive for low levels of melamine. None went to slaughter. According to the state veterinarian, none of the suspect feed was fed to the hogs. Federal tests on the feed have come up negative. The positive urine tests could not be immediately explained, although contaminated feed could have escaped detection during tests, the FDA said.
• NORTH CAROLINA: A farm with 1,400 hogs is under quarantine. It shipped 54 animals to a slaughterhouse, where they are on voluntary hold.
• UTAH: Eight hogs sent to slaughter by one farm remain on hold. Also on hold are 3,300 hogs at a second farm, as well as 40 to 50 carcasses at a slaughterhouse supplied by that producer. Meat from no more than 100 other hogs from the producer, all processed earlier by that same plant, may have entered the food supply, Andrews said.
• KANSAS: Meat from 195 hogs from a single producer may have entered the food supply via a Nebraska slaughterhouse. The farm is holding another 150 hogs.
• OKLAHOMA: A show hog operation purchased contaminated feed but no hogs have gone to slaughter.

In addition, an Ohio hog farm has been cleared.

Each year, about 105 million hogs are slaughtered and processed in the United States.