Chinese manufacturers might have intentionally added a chemical linked to pet deaths and illnesses into a protein-powder ingredient in pet foods, federal government regulators said Thursday.
Stephen Sundlof, chief veterinarian for the Food and Drug Administration, said melamine, which has turned up in more than 100 brands of cat and dog food, might have been used to falsely boost the apparent nutritional content of rice protein.
"That's still a theory, but it certainly seems to be a plausible one," he said.
Melamine, an ingredient in plastics and fertilizers that could lead to kidney failure in animals, has contaminated rice protein and wheat gluten in pet foods produced in Canada and the United States.
The chemical compound reportedly also has tainted corn gluten added to pet food sold in South Africa, the FDA said.
Three protein sources from China containing melamine adds credibility to the theory that it was used intentionally, Sundlof said.
FDA officials said they are investigating whether the melamine might have been added intentionally as a way to charge more for an inferior product.
But the FDA added that it would not be able to check its theory without getting approval from the Chinese government to inspect the factories where the rice protein and wheat gluten were produced. The FDA said it "fully expects" to get cooperation from the Chinese government.
The Chinese government has said that the contaminated wheat gluten was not meant for pet foods and therefore was not its regulatory responsibility.
The FDA said it had traced the contaminated wheat gluten to Xuzhou Anying Biologic Technology Development Co., in Jiangsu province just north of Shanghai.
The company's general manager, Mao Lijun, said earlier this week that his company was investigating the matter. He declined to answer questions.
The FDA also said domestic manufacturers share some responsibility for ensuring the safety of their pet foods.
"There is an industry responsibility to know who their suppliers are and to exercise some diligence," said Michael Rogers, head of the FDA's Division of Field Investigations.