The following shall be sufficient and be deemed a lawful fence only as to horses, cattle, and mules: any enclosure made by stretching not less than five (5) strands of barbed wire tightly between posts firmly set in the ground, or between growing trees and posts firmly set in the ground, not more than twenty feet (20′) apart; the topmost wire not less than four and one-half feet (4½’) from the ground, the bottom wire not less than six inches (6″), and the next to the bottom wire not less than fifteen inches (15″) from the ground.