U.S. Department of Agriculture Chief Veterinary Officer Dr. John Clifford said the 12-year-old cow's herd is under a USDA holding order while investigators identify cattle born the same year, the year before and the year after, as well as any offspring and the cow's mother, if it is still alive.
The animal's age made it likely that it was infected before the 1997 ban on feeding protein from ruminants like cows and sheep to other cattle, he said.
The animal was delivered in November to a Waco pet food plant, which refused to process it because it was unable to walk.
The plant, Champion Pet Food, which produces ground beef for racing greyhounds, confirmed Wednesday the cow arrived on Nov. 15 after being sold at an auction barn and was found dying on a truck, the Fort Worth (Texas) Star-Telegram reported.
Clifford refused to identify the ranch where the infected cow was raised.