The pilot reported that the flight’s purpose was to guide cattle while at low altitude. During a turn with trees in the vicinity, the pilot heard a noise and felt a bump in the flight controls. The helicopter began to spin uncontrollably and impacted terrain, which resulted in substantial damage to the main rotor system, tail rotor system, fuselage, and tail boom. Examination revealed that the tail rotor gear box and tail rotor (TR) blades were separated from the helicopter. The gear box housing fracture surfaces were consistent with overload. The size/shape of the dents and tree debris lodged in the leading edge of the TR blades was consistent with the size/shape of the tree branches that were broken. The pilot reported that there were no preaccident mechanical malfunctions or failures that would have precluded normal operation.