THURSDAY, April 26 (HealthDay News) -- Some 6,000 hogs have been quarantined across eight U.S. states because they may be eaten contaminated salvage pet food, the U.S. Food and Drug Administration announced late Thursday.

At the same time, U.S. Department of Agriculture officials said that meat from 345 hogs that ate tainted feed has already entered the U.S. food supply, the Associated Press reported.

The quarantined hogs are on farms in California, New York, South Carolina, North Carolina, Utah, Kansas, Oklahoma and Ohio, the AP said. And the USDA reported that swine from slaughterhouses in Kansas and Utah may have entered the food supply. Government officials, however, consider the threat to human health to be very low.

The swine are thought to have been exposed to food contaminated by two chemicals, melamine and cyanuric acid, that was sent as salvage by companies who have had to recall massive quantities of dog and cat food as the pet food recall rolls on.

"Today we notified eight states that adulterated swine products will not be approved to enter the food supply," Captain David Elder, director of the FDA's Office of Enforcement Office of Regulatory Affairs, said during a late afternoon teleconference.

He stressed, however, that "based on information currently available, the FDA and the USDA believe the likelihood of illness after eating such pork is extremely low. However, the agencies also believe it is prudent to take this measure."

According to the AP, potentially contaminated pet food scraps may also have found their way to a poultry feed mill in Missouri. That case remains under investigation.

Melamine was first found in pet foods manufactured by the Canadian company Menu Foods, which began its widely publicized recall March 16. That recall included moist dog and cat foods made with melamine-contaminated wheat gluten imported from China.

The recall has since expanded to other pet food manufacturers and other pet food ingredients, including imported rice protein concentrate and corn gluten.

In a new recall added on Thursday, Chenango Valley Pet Foods, of Shelburne, N.Y., announced it was recalling a variety of shipments of dry pet foods, including selected packets of: Doctors Foster & Smith Chicken & Brown Rice Formula Adult Lite Dog Food; Doctors Foster & Smith Chicken & Brown Rice Formula Adult Lite Cat Food; Lick Your Chops Lamb Meal, Rice & Egg Cat Food, and Bulk Chicken & Brown Rice Formula Adult Lite Dog Food.

In addition to melamine, the FDA has now found cyanuric acid in the rice protein concentrate and wheat gluten used in much of the pet food recalled over the past few weeks.

Like melamine, cyanuric acid is a chemical that can be used to boost the apparent protein content of foods. It is most often used as a stabilizer in outdoor swimming pools and hot tubs.

"The combination of melamine and cyanuric acid is of concern to human and animal health," Elder said. "Melamine, at detected levels, is not a human health concern," he added.

The USDA will compensate hog farmers affected by the tainted pet food, Kenneth Peterson, an assistant administrator for field operations at the USDA Food Safety and Inspection Service, said during the teleconference.

"The pork and pork products from these animals will be destroyed," Peterson said. Each year, more than 105 million hogs are slaughtered in the United States, the AP noted.

Elder also announced that the FDA has been granted visas to go to China to look for the sources of the contamination.

On Thursday, China banned melamine from its food products, but rejected the charge that that the substance caused the pet deaths, the AP reported.

China's Foreign Ministry said in a statement that there was no evidence to support the FDA's claim but that it would cooperate with the United States to find out what actually killed the animals.

"At present, there is no clear evidence showing that melamine is the direct cause of the poisoning or death of the pets," the statement said. "China is willing to strengthen cooperation with the U.S. side ... to find out the real cause leading to the pet deaths in order to protect the health of the pets of the two countries."

More information

For more information on pet food, visit the U.S. Food and Drug Administration.

SOURCES: April 26, 2007, teleconference with Captain David Elder, director, Office of Enforcement Office of Regulatory Affairs, U.S. Food and Drug Administration; Kenneth Peterson, assistant administrator for field operations, Food Safety and Inspection Service, U.S. Department of Agriculture; April 26, 2007, statement, CHenango Valley Pet Foods; Associated Press

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