The pilot was engaged in a muster of cattle for a brucellosis test. He was chasing a calf that had broken away from the main herd. When the animal turned towards the helicopter, the pilot attempted to take evasive action. He felt the aircraft rock, and believing that it had been struck by the animal, pulled it up to about 40 feet above the ground. The aircraft began to yaw. During the subsequent landing, while still yawing, the landing skids collapsed. The investigation revealed that the animal had not contacted the aircraft. During the evasive action taken by the pilot the tail rotor had contacted the ground which resulted in the loss of directional control. This accident was not the subject of an on-site investigation.