LITTLE ROCK, Ark. - Tests of two Chinese brands of dog treats sold at Wal-Mart stores found traces of melamine, a chemical agent that led to another massive pet food recall in March, a spokeswoman said Tuesday.

Wal-Mart Stores Inc. quietly stopped selling Chicken Jerky Strips from Import-Pingyang Pet Product Co. and Chicken Jerky from Shanghai Bestro Trading in July, after customers said the products sickened their pets.

No recall was announced at that time, but Wal-Mart said in a statement Tuesday that customers who bought one of the products should return it to the nearest store for a refund.

Company spokeswoman Deisha Galberth said 17 sets of tests done on the products found melamine, a contaminant that's a byproduct of several pesticides.

"There were very small amounts of melamine found," Galberth told The Associated Press. "The amounts were so small the laboratory recommended more testing."

Galberth had said late Monday that Wal-Mart pulled the products off store shelves based on the customer feedback but wanted to complete the testing before announcing anything publicly.

More than 150 brands of pet food were recalled earlier this year after U.S. inspectors said wheat gluten from China that was used to make the food was tainted with melamine. An unknown number of dogs and cats died.

Since then, other Chinese products including tires, toothpaste, seafood, juice, and toys decorated with lead paint have been recalled or have come under scrutiny.

Galberth said she couldn't say if the amount of melamine found in its dog treats would be enough to sicken or kill a dog that ate the suspect products. The Delaware County (Pa.) Daily Times reported last week that a woman claimed her 2-year-old Chihuahua died after eating some of the products. According to the report, an autopsy found the dog died of an infection caused by toxic bacteria.

Wal-Mart's statement Tuesday said customers should be especially wary of jerky from Shanghai Bestro Trading with the UPC number 0087784900006 and item number 839751.

The Food and Drug Administration did not list the two Wal-Mart products on its recall Web site Tuesday. As recently as 2005, the FDA blocked some pet treat imports from Pingyang Pet Product Co. because of contamination with salmonella.

Galberth said she was not aware of the FDA's previous concerns with Pingyang but said the company was working with the FDA and manufacturers. She said she did not immediately know where the Chinese companies were based.

Bentonville-based Wal-Mart, the world's largest retailer, pulled the products from shelves July 26 and placed a computerized block on all cash registers to prevent workers from selling the products. Galberth said she did not know how many stores sold the treats.

"Generally, we won't do a pull-and-hold unless most stores are impacted," she said. "There's a high likelihood many of our stores would have been impacted by this one."

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