In agriculture, fences are used to keep animals in or out of an area. They can be made from a wide variety of materials, depending on terrain, location and animals to be confined. Most agricultural fencing averages about 4 feet (1.2 m) high, and in some places, the height and construction of fences designed to hold livestock is mandated by law.
The principle of wire fences is that they are supported mainly by tension, being stretched between heavy strutted or guy-wired posts at ends, corners, and ideally at intervals in longer stretches (every 50 to 300 metres, 150 to 1000 feet). Between these braced posts are additional smaller wooden or metal posts which keep the wires spaced and upright, usually 3 to 6 metre (10 to 20 feet) apart, depending on the style of fencing used.
Chain link fence with barbed wire on top.
Detail of barbed wireThe Industrial Revolution brought the first barbed wire (also "barbwire" or just "barb") fences, which were widely used after their introduction in the mid-19th century. This technology made it economically feasible to fence rangeland for the first time. In the United States, introduction of barbed wire contributed to the range wars of that century, as various ranch interests attempted to use barbed wire fences to claim exclusive access to the best pasture and water resources, including those lands in the public domain. It also exacerbated tensions between cattle ranchers and crop farmers, partly when access to water was involved.
High tensile wire
High tensile (H-T or HT) fencing is a special hard, springy steel wire was introduced in the 1980s and has slowly gained acceptance. The wire may be a single strand plain or barbed wire, or woven mesh, and is capable of much higher tension than mild steel. It permits the use of wider post spacings and is neither stretched easily by animals, nor by fallen trees or branches. It can be insulated and electrified. Because of the wide spacing of the posts, thin metal or wood spacers (or "droppers") may be attached to the wires between posts to maintain their spacing.