Millions Of Chickens Fed Tainted Pet Food
• Likelihood of human illness after eating such chicken is "very low"
• No human illness linked to the tainted feed reported to FDA, USDA
NEW YORK (CNN) -- People have eaten millions of chickens that were given feed tainted with recalled pet food, federal officials said Tuesday, though they said the threat to human health is minimal.
The announcement came after an investigation of chicken farms in Indiana found that 38 of the facilities had given contaminated feed to poultry raised for human consumption, and that 2.5 million to 3 million people ate them.
The officials added that they expect to discover that chickens on possibly hundreds of farms in other states were also given tainted feed.
In a teleconference with reporters, an official with the Food and Drug Administration said no recall has been issued because "the likelihood of illness after eating chicken fed the contaminated product is very low." (Blog: Melamine 'dilution' means human risk is probably lower )
No human illnesses have been reported related to the feed, officials with the FDA and the U.S. Department of Agriculture said.
Last week, as part of its investigation into the nationwide pet food recall, the FDA ordered that all vegetable protein imports from China used in human and animal food be detained.
The products include wheat gluten, rice gluten, rice protein, rice protein concentrate, corn gluten, corn gluten meal, corn byproducts, soy protein, soy gluten proteins and mung bean protein.
FDA officials said Tuesday that they have found no evidence that tainted wheat gluten was added directly to any food products sold in the United States.
Two FDA investigators are in China and a third was en route working with the Chinese government's General Administration for Quality Supervision, Inspection and Quarantine to investigate the sources of the contaminated products. (Watch more on concerns about China's food safety)
It was unclear how long tainted food additives from China have been entering the United States.
"Clearly that is a concern if that has been going on for a long period of time," said Dr. David Acheson, who had been appointed earlier in the day to the newly created position of FDA assistant commissioner for food protection.
The FDA's investigation began in March after at least 17 cats and dogs died of kidney failure linked to the tainted pet food. The urine of cats that ate the food tested positive for melamine, an industrial chemical used in the manufacturing of plastic utensils and fertilizer.
Investigators suspect that melamine, in combination with a rice protein additive imported from China and found to contain cyanuric acid, may cause crystals to form in the kidneys, shutting them down. Cyanuric acid is used as a stabilizer in outdoor swimming pools and hot tubs.
"We had one case recently where the cat's kidneys were completely obstructed and when we went to surgery to relieve the obstruction there was no normal stone, instead the ureters were completely full of these melamine-type crystals," said Dr. Louise Murray, director of medicine at New York's Bergh Memorial Animal Hospital.
The National Chicken Council, which represents U.S. poultry producers, marketers and processors, said Tuesday in a written statement: "We are confident that any poultry producers involved will work expeditiously with the government to resolve this matter to the satisfaction of the government agencies."
Leftovers link possible
NCC spokesman Richard Lobb said Chinese producers appear to have been spiking their feed with the contaminants to make it appear that it contains more protein than it does. Some tests for protein content measure nitrogen content, an ingredient of melamine and cyanuric acid.
Lobb said the chicken feed may have been contaminated as a result of a practice common among pet food manufacturers -- they sometimes sell their leftover material to manufacturers of chicken and pig feed.
"It's like cooking cupcakes -- you get some of the dough on the pan, you scrape it off and throw it away. What they're saying is that somebody bought that material and it got mixed in corn and soybean that gets manufactured in poultry feed," he said.
"The dilution factor is enormous. You have a relatively small amount of pet food byproducts used," Lobb said. "It's a safe and wholesome product to use."
Representatives of Perdue and Tyson Foods -- two of the largest U.S. chicken producers -- said Tuesday in letters to supermarkets that they do not use protein ingredients from China in their feeds.
Last week, FDA officials said 6,000 hogs that may have ingested tainted pet food entered the human food supply. Pork producers in seven states -- California, Kansas, North Carolina, New York, South Carolina and Utah -- are being investigated for buying adulterated feed.
The agency also reported last week that it has received more than 17,000 consumer complaints related to the recall, including reports of approximately 4,150 dog and cat pet deaths.
More than 150 brands and 5,300 pet food products have been recalled. Companies that produced affected items include Menu Foods, Hill's Pet Nutrition, P&G Pet Care, Nestle Purina PetCare, Del Monte Pet Products and Sunshine Mills have been recalled in cooperation with the FDA. The first recall was initiated March 16 by Menu Foods.
CNN's Katy Byron, Joe Johns, Miriam Falco and Elizabeth Cohen contributed to this report.