The documentary Mad Cowboy tells the story of a former cattle rancher, Howard Lyman, who is now vegan. He made the transition after developing a spinal tumor that almost paralyzed him. This tumor was caused by the chemicals used in agriculture. He raises awareness about how an animal-based diet is the leading cause of cancer, heart disease, and obesity in America. He also talks about the propaganda of the beef and dairy industries and how his life has changed since he stopped raising animals for food.