The nation's first domestic case of mad cow disease (search) has been traced to a 12-year-old Texas-born cow destined to become pet food until the federal government's testing program kicked in.

The animal was first identified as a potential case of the brain-wasting disease at Waco-based Champion Pet Foods Inc. (search), which is under contract to take samples from animals with questionable health.

The animal did not enter the human or pet food supply, officials said.

"The safety of our food supply is not in question. I am very confident that our interlocking safeguards are effective, and this case is evidence of that," said USDA (search) Chief Veterinarian John Clifford.

It was the first time the disease has been confirmed in a U.S.-born cow. The other U.S. case, confirmed in December 2003 in Washington state, was in a dairy cow imported from Canada.

The infected cow was brought already dead to Champion Pet Food on Nov. 15, owner Benjy Bauer said. His employees took samples and sent them to the Texas Veterinary Diagnostic laboratory at Texas A&M University.

The lab, which tests cows from Texas, New Mexico, Arkansas and Louisiana, is one of several the Agriculture Department uses to screen the nation's cattle for mad cow disease.

"We pay people to bring them to us," said Bauer, who said he did not know the origin of the infected cow. "That way we get them and that way we can test them. We just do what the government asks us."

After the first test on the animal came back as "inconclusive," a USDA representative took the carcass to the Texas Veterinary Diagnostic Laboratory, where it was incinerated.

Agriculture Department officials would not identify the cow's owner or the town where the animal came from, although they said the animal had only one owner and was raised in Texas.

Mad cow disease is medically known as bovine spongiform encephalopathy, or BSE, which causes spongy holes in the brain. In people, a rare but fatal form of the disease called variant Creutzfeldt-Jakob disease has been linked to eating infected tissue from cows.

Clifford said the cow was linked to a Texas herd through DNA testing. He said the herd had been quarantined, but he wouldn't say how many animals it included.

Given the cow's age, agriculture officials believe it was most likely infected by consuming feed before the 1997 ban forbidding the use of cattle parts in cattle feed. The department and the Food and Drug Administration are trying to trace the history of the herd's feed.

Officials also are trying to identify herd mates born within one year of the infected cow's birth as well as any offspring born within the past two years, even though "it is highly unusual to find BSE in more than one animal in a herd or in an affected animal's offspring," Clifford said.

Bauer said his company is not connected to Champion Pet Food of Alberta, Canada, which recalled some of its dry dog food in 2003 because it may have come from a Canadian cow that tested positive for mad cow disease.

Bauer's firm produces several blends of dog food, primarily for greyhounds. He owns another plant in Clovis, N.M., which also takes samples for the government, Bauer said.

"We send samples for testing every day," he said.

Texas is the leading cattle state in the nation with 13.8 million head or 15 percent of the total U.S. cattle inventory. In 2004, cattle had a total economic impact of $14 billion on the state's economy, state agriculture figures show.

Members of the state's beef industry were quick to remind consumers that the cow never entered the food supply, and that the nation's beef supply is safe.

"Consumers have a safe product," said Matt Brockman, a spokesman for the Texas and Southwestern Cattle Raisers Association. "The firewalls continue to be a testament to that safety, whether it's consumers in Fort Stockton, Texas, or in Fort Lauderdale, Florida."