Sixty-seven animals were removed for testing from the same Texas herd that was home to the first confirmed case of mad cow disease in an animal born in the US.

Investigators have been working to identify offspring and herd mates born within a year of the infected cow's birth. The infected cow was a 12-year-old Brahma cross beef cow.

67 Cows Removed for Testing

Twenty-nine adult cows were removed from the herd on Wednesday, the department said. They were taken to a collection site and euthanized, and tissue samples were removed for testing.

The department said Saturday that those 29 adult cows tested negative, according to the National Veterinary Service Laboratory in Ames, Iowa. Samples from an additional 38 cows received Friday are pending, the department said. In all, 67 animals were removed from the herd for testing.

Agency Watchdog Ordered Third Test

The infected cow spent its entire life on the same farm, which the government has not identified. It was sold through a livestock market on Nov. 11 but was dead on arrival four days later at a slaughterhouse, the department says. It was then taken to a pet food plant in Waco, Texas, which did not use it for food but removed brain tissue for testing.

Screening called "rapid test" indicated the presence of mad cow disease in the animal, but results from another test were negative. The government announced that the animal was free of the brain-wasting disease.

Last month the agency's internal watchdog ordered a third type of test that came back positive. A lab in England confirmed the results June 24.