The pilot was herding cattle when the helicopter's tailrotor struck a mesquite tree branch. The helicopter began a yaw to the right and a made 2 full rotations as the pilot maneuvered to open terrain. The pilot rolled the throttle off, stoppied the yaw, and the helicopter landed hard. The pilot did not report any mechanical anomalies which contributed to the accident. An examination of the helicopter conducted by inspectors from the Federal Aviation Administration did not reveal any mechanical anomalies.