The helicopter pilot reported that he was flying parallel to a 10 ft barbed wire fence while herding cows into a livestock pen. While maneuvering, the helicopter's tail rotor struck the fence and the helicopter spun multiple times to the right. The helicopter ascended about 10 ft and the pilot retarded the throttle and lowered the collective to the full down position to minimize the rapid right spin. The helicopter impacted the ground and came to rest upright causing damage to the tail rotor drive system and tail boom.