The case of bovine spongiform encephalopathy was detected during routine surveillance at a livestock market, the USDA said in a statement.
In the four previous findings of BSE in the U.S., one case in Washington state in December 2003 was classical, involving a cow brought in from Canada.
While the case of classical BSE in 2003 "shocked the world and shut down a big chunk of exports," the industry has since made changes to ensure that an infected cow would never enter the human food chain, Brett Stuart, a founding parter at Denver-based market researcher Global AgriTrends, said in a telephone interview.
On the Chicago Mercantile Exchange, cattle futures for October delivery fell 1.5 percent to close at $1.16875 a pound.
In the month of December 2003, the most-active contract plunged 21 percent after the classical case was reported.