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Agricultural fencing
From Wikipedia, the free encyclopedia
In agriculture, fences are used to keep animals in or out of an area.
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In the past, livestock would roam freely and were fenced out of areas, such as gardens and fields of crops, where they were unwanted. Over time, especially where crop agriculture became dominant and population density of both humans and animals was significant, livestock owners were made to fence their animals in.
The earliest fences were made of available materials, usually stone or wood. In areas where field stones are plentiful, fences have been built up over the years as the stones are removed from fields during tillage and planting of crops. The stones were placed on the field edge to get them out of the way. In time, the piles of stones grew high and wide.
In other areas, fences were constructed of timber. Log fences or split-rail fences were simple fences constructed in newly cleared areas by stacking log rails.
A later development was the sunken fence, or "ha-ha," a type of wall built by digging a ditch with one steep side (which animals cannot scale) and one sloped side (where the animals roam).
The tradition of fencing out unwanted livestock prevails even today in some sparsely populated areas. Until the beginning of the 21st century, most states in the American West still followed this tradition and were called "open range" ("fence out") states, in contrast to Eastern and Midwestern states which have long had "fence in" laws where livestock must be confined by their owners. Though the open range was part of the western tradition, over time, open range was limited long before it was eliminated completely; first came an obligation to keep cattle from roaming onto state and federal highways, where collisions with fast-moving cars and trucks created a public safety hazard. Then, areas where crop agriculture predominated would voluntarily choose to make certain heavily farmed areas a "herd district," where livestock needed to be fenced in. Over time, court cases steadily limited the application of open range law until the present day, where it is the exception rather than the rule in many parts of the American West.
The Industrial Revolution brought the first barbed wire 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. The introduction of barbed wire contributed to the range wars of that century, as it exacerbated tensions between landowners seeking exclusive control over large tracts of land and traditional transient users of that land.
Barbed wire was made by many manufacturers in an almost endless variety of styles. For the most part these were functionally identical. The differences reflected peculiarities of each manufacturing process rather than deliberate design of the end product. Sections of unusual barbed wire are collected by some enthusiasts.
The traditional barbed wire used from the late 19th through most of the 20th century was made from two mild steel wires, usually of about 12 or 14 gauge, with about 15-30 twists per metre. Steel barbs were attached every 10-20 cm. Barbs had either two or four points, with the two point design using somewhat heavier and longer barbs. The relative merits of two point vs. four point wire are the subject of deeply held views among many farmers and ranchers, to the extent that both types are still made today.
Barbed wire is typically run on wooden posts, either commercially grown in plantations or, particularly in the American West, often posts that have been cut from nearby trees. Wire is attached to the posts using fencing staples. Typically four or five strands of barbed wire make up a fence. Posts are usually spaced 3-6 m apart.
In areas where there is more rainfall, either rot-resistant wooden posts or steel posts are used. Wood with natural rot resistance, such as oak and juniper, was often used until it became in short supply in the 1950s. Then, chemically treated pine and spruce posts became prevalent. Creosote, pentachlorophenol, and chromated copper arsenate were all widely used.
In the 1970s, high-tensile barbed wire became available. It is lighter in gauge (usually 16 gauge) but, due to higher carbon content, just as strong as the traditional mild steel. Advantages include lighter weight and lower cost.
Barbed wire is effective for containing cattle and horses. However, while commonly used in many areas, it is not recommended for horses due to the high risk of injury that can occur when a fast-moving animal with long legs runs into it or puts a leg through the strands.
Smooth wire is installed and used in a manner similar to barbed wire, and is essentially the same product, minus the barbs. Its primary advantage is that it is less likely to cause lacerations and cuts if an animal becomes entangled in it. However, without barbs, some animals will not respect the fence and will lean on it until it is stretched out of shape or loosened from the posts. Smooth wire fencing is often used as an inexpensive material to more safely contain horses and other animals that run a high risk of entanglement.
Barbed wire cannot effectively contain pigs, sheep, or goats. Where these animals are to be fenced, woven wire is used instead, often with one or several strands of barbed wire at the top. For swine, a ground-level barbed wire strand is used as well to prevent digging. Woven wire is costly to purchase and time-consuming to install. Woven wire with large openings, known as "sheep fence" in the western United States and Ringlock in Australia, is particularly dangerous for native animals, such as kangaroos and wallabies that attempt to jump such fences. They can be easily trapped when their large back feet clip the ringlock fencing and get caught. While they can be cut out, they are often so injured that they do not live.
Woven wire with large squares is also dangerous for horses as they can put a foot through the wide squares and then become tangled in the fence. Horses and ponies are safer kept inside woven wire fence with squares of smaller dimensions, such as "no climb" fence with squares that are approximatly two inches by four inches.
Electric fencing became available in the 1950s and has been widely used for temporary fences and as a means to improve the security of fences made of other materials. It is made using lightweight steel wire (usually 14-17 gauge) attached to posts with insulators made of porcelain or plastic. A fence charger places an electrical pulse from ground to the wire about once per second. The pulse is narrow and usually around 5-20 kV. Animals receive a painful but harmless shock when contacting the wire, and learn to stay away from it.
High tensile (H-T or HT) fencing using smooth, heavy gauge (usually 12.5 gauge, 2.5mm) steel wire was introduced in the 1980s and has slowly gained acceptance. It permits the use of wider post spacings and offers improved stock safety compared to barbed and woven wire fences. It can be insulated and electrified. Trellising for horticultural purposes is generally constructed from HT wire as it is able to withstand a higher cropping load. Joining HT wire is difficult because of its stiffness and its reduction in strength when bent to form a knot.
Fences of wood, stranded cable, and pipe are used where cost is less of a consideration, particularly on horse farms, or in pens or corrals where livestock are likely to challenge the fence. Synthetic materials with wood-like qualities are also used, though they are the most expensive option in most situations. In some areas, these types of fencing materials can be cost-effective if plentiful. For example, scrap pipe is often easily obtained at a low price if oil fields are nearby, and wood rails can sometimes be harvested from the owner's own land if it contains suitable standing timber.
All types of agricultural fencing require regular maintenance to ensure their effectiveness. Cattle and horses are strong enough to go through most types of fence by main force, and occasionally do so when frightened or motivated by hunger, thirst, or sex drive. Weather, flood, fire, and damage from vandals or motor vehicle accidents can do similar damage and may allow livestock to escape.