Sixty-seven cows culled from the herd of an animal infected with mad cow disease have tested negative for the disease, the Agriculture Department (search) said Sunday.

Testing was conducted on two groups removed from the herd at an undisclosed ranch in Texas (search); 29 cows were tested on Wednesday, 38 on Friday. Results released Sunday on the second group were negative, the same finding the department had announced Saturday for the initial test group.

The National Veterinary Services Laboratory (search) in Ames, Iowa, conducted the tests.

The infected animal, a 12-year-old Brahma cross beef cow, had spent its life at the ranch, the department said. After a livestock market sold the cow on Nov. 11, it arrived dead at a slaughterhouse a few days later and was then taken to a pet food plant in Waco, Texas. The animal was not used for food, and its brain tissue was removed for testing.

One test indicated the presence of mad cow disease, but results from a subsequent test were negative. Several months later, the department's inspector general ordered a third test, which showed the disease. A series of tests at a lab in Britain confirmed on June 24 the second case of mad cow disease in the United States.