The second US case of mad cow disease happened in a beef cow from Texas, which was killed last November at a plant for pet food, the US Department of Agriculture said Wednesday.

DNA test results helped identify the infected cow, which "was born and raised in a herd in Texas and was approximately 12 years old," USDA chief veterinarian John Clifford said in a statement.

Clifford said the source herd was currently under a hold and the USDA would also test the offspring of the infected cow and other cows of its age or born one year before or after it.

According to him, the infected cow was born before August 1997 when the United States banned the use of cattle parts in cattle feed, which is how the mad cow disease is believed to spread.

"I emphasize that this animal did not enter the human food chain," he said, adding that the plant at which the cow was sampled is a "pet food plant that does not handle animals for human consumption and, in this case, did not use the animal in the production of pet food. The animal remains were incinerated."

The USDA chief veterinarian said the discovery of the new case of mad cow disease showed the USDA's "interlocking safeguards" in place are effective.

"The safety of our food supply is not in question."

The second US case of mad cow disease was announced on June 24 after being confirmed by tests at an internationally recognized laboratory in England. Previous US tests produced conflicting results, prompting the verification.

The first US case was reported in December 2003, in a Washington State dairy cow imported from Canada.

People eating animal meat products contaminated with mad cow disease, or bovine spongiform encephalopathy (BSE), can develop a human variant of the fatal brain-wasting illness called Creutzfeldt-Jakob disease. The brain disorder has killed more than 150 people, mostly in Britain, where an outbreak was reported in the 1990s.

Source: Xinhua