HOUSTON -- In an exclusive report Thursday night, News2Houston learned that the U.S. Food and Drug Administration is examining the contents of pet food after receiving complaints from veterinarians that it's taking longer to put pets to sleep or sedate them.

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What's Inside Pet Food?

The FDA admits to finding trace amounts of the powerful drugs used to kill animals in pet food before.

Dr. Mike Huddleston, a veterinarian, said that he's never heard of the practice but acknowledges that the effects could be devastating.

"The amount of overdose of the barbiturate that you give I'm sure would be in all the tissue of the animal," Huddleston said. "So if you use that animal in dog or cat food that would definitely cause serious problems, there's no question."

The issue of pets in food came to light, largely from a book written by Ann Martin titled, "Food Pets Die For," in which she takes on the multi-billion dollar pet food industry.

Martin said in her book, "The industry is virtually self-regulated. Just about anything and everything is fair game for use in pet food …"

According to Martin, some of items found in pet food include the following:

• Condemned and contaminated material from slaughter house facilities
• Road kill
• Dead, diseased and dying animals
• Euthanized companion animals

"It certainly could occur," said Dr. Roger Hoestenback head of the Office of Texas' Feed & Fertilizer Control Service. "How much of that is intentional? I doubt any of it is."

Hoestenback said that pet food manufacturers are the biggest customers of slaughter houses and rendering plants, which grind up animal carcasses.

"They would not knowingly put rendered dogs and cats," Hoestenback said. "It's not premium product. For their business it would be suicide."

"When you go shopping for Fido, be sure to read the labels," News2Houston reporter Rachel McNeill said. "You won't find cat, dog or diseased livestock written on the back. Those quote, unquote protein sources can be listed as meat or bone meal or meat-by-product."

"As long as its mammalian tissue, then that meets that definition," Hoestenback said.

FDA pet food test results are expected to be released later this month.

A representative with the Pet Food Institute, which represents pet food makers, denies using any cat or dogs in its products, and that the industry follows strict federal and state guidelines.