The Utah Department of Agriculture and Food announced Wednesday that, as a precautionary measure, hogs at three northern Utah farms have been placed under a "hold order," while tests proceed to determine whether they ingested tainted feed.

On Tuesday, the U.S. Food and Drug Administration announced that hogs in Utah and five other states may have eaten food contaminated with an industrial chemical linked to a massive recall of pet food and animal feed. According to the FDA, it appears that some of the contaminated pet food was sent as salvaged feed to hog producers in Utah, California, North and South Carolina, New York and possibly Ohio.

The FDA tested hogs in California and the Carolinas, and levels of melamine were detected in their urine. Melamine is a non-protein nitrogen source with a variety of uses, including fertilizer.

Questions outnumbered answers Wednesday, as state and federal officials worked to identify whether animals had ingested the contaminated food, whether ingesting melamine affected hogs the same way it appeared to affect some pets, whether melamine had or could make it into the human food market, and whether it was harmful to humans.

What is known is that the six states in question all received feed from American Nutrition, an Ogden pet food company, according to UDAF Commissioner Leonard Blackham. American Nutrition reported earlier this month that its feed might have contained contaminated rice protein concentrate imported from China, launching an FDA investigation.

While the FDA continues its tests on whether the feed is contaminated, Blackham said the UDAF has ordered reagents from New Jersey to conduct its own urine tests to determine the presence of melamine. Sixty hogs from the three Utah farms will undergo urine tests, said state veterinarian L. Earl Rogers. The results likely won't be available until next week.

No hogs have become ill or died under suspicious circumstances, Blackham said.

As of Wednesday, several questions remained, including:

• Whether animals at any of the three Utah hog farms ingested contaminated food. The UDAF declined to identify the farms but said each was under a voluntary "hold order" discouraging the sale of hogs into the market.

• Whether any contaminated animals have made it to market.

• Whether ingesting the levels of melamine in the contaminated feed has detrimental effects on the hogs, or humans.

Little is known about melamine, according to Utah Health Department spokeswoman Charla Haley. There is no substantive research on the health effects of melamine on humans.

"All of our actions are presumptive," Rogers said. "We still don't have any concrete test results."