The Associated Press reports the second U.S. case of mad cow disease was a cow from Texas killed last November.
The AP quotes two government officials, who spoke on condition of anonymity.
The U.S.Department of Agriculture planned an announcement later.
AP reports USDA officials traced the infected cow to a rendering plant for animals unfit for human consumption.
Ag authorities have said the cow was a so-called "downer" that couldn't walk.
The animal was more than eight years old when it arrived at the plant.
The U.S. banned using cattle parts in such feed since 1997 following an outbreak of mad cow disease in Britain.
Governor Rick Perry late Wednesday afternoon issued the following statement:
“I want to urge calm and reassure the public that they can have the highest confidence in our beef supply, and the safeguards we have in place to protect the public from the spread of BSE. There is not, nor has there ever been, a known instance of BSE contaminating the food supply in Texas or anywhere else in the United States. The animal in question was not processed into food or any other product. Texans can be sure that the beef they buy at their local supermarkets or restaurants is as safe today as it was yesterday, and I encourage Texans to continue to enjoy Texas beef products.”