The ranchers say Ms Winfrey and a vegetarian activist who appeared on her show in 1996 defamed the quality of US beef and caused them millions of dollars in losses when stock prices fell. Texas is one of 13 states where disparaging the quality of food is a crime.
The charges relate to remarks by Howard Lyman, director of a campaign launched by the Humane Society called Eating with Conscience, to the effect that in America thousands of cows died of unknown causes every year, were ground up and fed to other cows - the same conditions blamed for the BSE epidemic in Britain.
Ms Oprah responded: "It has just stopped me cold from eating another burger." The suit accuses her and her team of failing to check their information; she argues that the show simply asked whether mad-cow disease could happen in the US.