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In agriculture, are used to keep 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 high, and in some places, the height and construction of fences designed to hold livestock is mandated by law.
A is the strip of land by a fence that is left uncultivated. It may be a hedgerow or a shelterbelt (windbreak) or a refuge for . If not too narrow, it acts as a habitat corridor.
The earliest fences were made of available materials, usually stone or wood, and these materials are still used for some fences today. 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 were simple fences constructed in newly cleared areas by stacking log rails. Earth could also be used as a fence; an example was what is now called 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).
In the United Kingdom, the law is different for private land and common land. On private land it is the owner's responsibility to fence livestock in, but it is the responsibility of landowners bordering a common to fence the common's livestock out.
Additionally, railways in the UK are fenced to keep livestock and people out, since it is a requirement to do so, unlike many other countries. Either Network Rail or the landowner are responsible for maintaining the fences.
Traditionally, wire fencing material is made of galvanization mild steel, but galvanized high-tensile steel is now also used in many places. To prevent sagging of the fence, which raises the risk of entanglement or escape, the wire is tensioned as much as the material will safely allow during construction by various means, including a hand-operated "wire stretcher" or "fence stretcher" (called a "monkey strainer" in some areas) or other leverage devices, a winch, or even by carefully pulling with a tractor or other vehicle.
Wire fences are typically run on wooden posts, either from trees commercially grown in or (particularly in the American West) cut from public lands. When less expensive or more readily available than wood, steel or are used, usually alternating every 2 to 5 steel posts with a more stable wood post. Non-electrified wire is attached to wooden posts using fencing staples (for intermediate posts, these are fitted loosely, not gripping the wire). Non-electrified wire is held on T-posts by means of wire "clips" made of smooth galvanized wire that wrap around the back of the post and hook onto the wire on either side of the post.
Other than in a truly desert climate, use of rot-resistant wooden posts or steel posts is advised. In the United States, 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, and these are also widely used in United Kingdom, together with chestnut. Creosote, pentachlorophenol, and chromated copper arsenate are all widely used in the US and elsewhere for treatment (although some of these chemicals are subject to legal controls).
Barbed wire has been 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 since the late 19th century and into the present day was made from two mild steel wires twisted together, usually of about 12 or 14 gauge, with about 15-30 twists per metre. Steel barbs were attached every . 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 barbed wire are the subject of deeply held views among many farmers and ranchers, to the extent that both types are still made today.
Typically four strands of barbed wire, with the lowest strand no more than from the ground and the top strand at least 48 inches above the ground, make up a legal fence in the western United States. Better-quality fences have five strands, older fences often had only three strands, and just two strands is widely used in Britain if only adult cattle are being contained. Other variations exist, depending on local laws and the purpose of the fence.
Barbed wire is particularly effective for containing cattle. In containing both cattle and sheep, one or two strands of barbed wire is used in conjunction with woven wire to both discourage cattle from reaching over the top of a fence and to keep sheep from crawling under. Though often used in many areas for , barbed wire is not advised; its use is considered poor Horse care. There is very high risk of injury occurring when a thin-skinned, fast-moving animal with long legs runs into it or puts a leg through the strands.
Joining HT wire is difficult because of its stiffness and its reduction in strength when bent sharply. However, it may be joined effectively with proprietary clips. HT wire is more expensive than mild steel, but because of the need for fewer posts, the overall cost of the fencing is usually comparable.
Because it does not stretch, animals are less likely to become entangled in HT wire. However, for the same reason, if an animal does become entangled or runs into a few strands at a high speed, it can be deadly, and is sometimes referred to as having a "cheese cutter" effect on the animal.
Trellising for horticultural purposes is generally constructed from HT wire as it is able to withstand a higher crop load without breaking or stretching.
Barbed wire fences cannot effectively contain smaller livestock such as pigs, goats or sheep. Where these animals are to be fenced, woven wire is used instead, sometimes with one or more strands of barbed wire at the top, and sometimes at the bottom to prevent animals from pushing under. For swine, a ground-level barbed wire strand or electrified wire is used as well to prevent digging beneath the fence.
Woven wire with large openings has some potential hazards. Large hoofed animals can put a foot through wide squares while grazing along the edge of the fenceline or while reaching over it, and then become tangled in the fence. A variation, called "field fence," has narrower openings at the bottom and wider openings at the top, which helps prevent animals from putting their feet through the fence. For example, horses in particular are safer kept inside woven wire fence with smaller openings, such as "no climb" fence with openings no larger than .
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 an uncomfortable but harmless shock when contacting the wire, and learn to stay away from it.
A variant, sometimes called "vinyl rail" or "strap fencing" consists of two or more vinyl-encased wires with vinyl or other synthetic between them to create a "rail" that is anywhere from wide. Some forms may be electrified by use of a special coating on the top wire of the "rail."
Vinyl fence is installed in a manner similar to plain high-tensile fence and must be stretched tight. Strong bracing of posts at corners and in the middle of long fencelines is required. Like other wire fences, keeping vinyl fencing tightened on a regular basis is key to safety and appearance.
A mesh form of vinyl fencing without internal wires is marketed as "deer fence" and used in some locations to augment other fencing to keep out wild animals. There are also some forms of vinyl fencing that look similar to vinyl-coated wire, but do not contain an internal wire, that are marketed to livestock owners. They are marketed as particularly safe, but their strength in containing animals is under debate.
A cattle grid is an obstacle used to prevent livestock, such as sheep, beeves, pigs, horses, or mules from passing along a road or railway which penetrates the fencing surrounding an enclosed piece of land or border.
Adding visibility to wire fences can help reduce wildlife collisions. Reducing the height of woven and strand wire fences to no more than can make it easier for wildlife to jump over with less risk of entanglement. Using barbless wires on top and bottom reduces cuts on wildlife which crawl under strand fences or those that try to climb over.
, made of cloth, metal and/or other materials, are sometimes used on fences to discourage wolves from entering a livestock enclosure.
Deer and many can easily jump an ordinary agricultural fence, and so special fencing is needed for farming goats or deer, or to keep wild deer out of farmland and gardens. Deer fence is often made of lightweight woven wire netting nearly high on lightweight posts, otherwise made like an ordinary woven wire fence. In areas where such a tall fence is unsuitable (for example, on mountains subject to very high winds), deer may be excluded (or contained) by a fence of ordinary height (about ), with a smaller one of about high, about away from it, on the same side as the deer. The additional width prevents deer approaching the fence close enough to jump it.
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