An invisible fence is an electronically generated 3-dimensional boundary that may take any geometrical shape to enclose an area, as well as surround individual animals, but is unseen by the eye. Invisible fences control animals that are wearing radio frequency (RF) receiving devices capable of capturing electronic signals.[1] The majority of signals used in invisible fences are between 3,000 hertz and 300 gigahertz. Invisible fences use sensory cues to invoke a change in an animal’s behavior or movement. Large animals can be controlled using audio cues, such as whistles, beeps, the human voice or any combination of them. Electric shock is also a cue used to control animal movement. Most commercial invisible fencing devices contain RF receivers that contain safety features aimed at preventing inhumane cuing, thus promoting an optimal animal experience. High frequency RF signals are emitted from a ground-based transmitter; however many invisible fencing systems will require many transmitters when the containment terrain is rugged and uneven.[2]
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The first commercial invisible fencing system was designed to contain house pets within a predetermined area, which was patented by Richard Peck, owner of Invisible Fence Company in 1974. Peck’s invisible fence was also the first borderless containment system used to contain livestock. In 1987 Peck successfully contained domestic goats to a limited area using RF receiving collars intended for household dogs.[3] In 1989 Thomas M. Quigley of Tri-Tronics successfully trained cattle to avoid specific areas, with less than two days of training using dog training collars. In 1990 Tri-Tronics successfully developed a RF receiver specifically designed for livestock to control heifers in Canadian fields and pens. In 1991 Brian Rose invented a RF receiver that controlled cattle with an electric shock that was delivered through a nose clip. In 1992 AgriTech Electronics developed an electronic ear tag which used audio and shock cues to control cattle and was researched to be 90% effective in preventing Texas steers and heifers from entering an exclusion zone.[3]
In 1997 Robert E. Marsh of AgriTech Electronics patented a fenceless animal control system using GPS location information. In Marsh’s device a portable unit is attached to each animal and includes a GPS receiver which provides an audible signal and an electrical shock.[4] Each portable unit further includes a suitable battery and appropriate electrical circuitry. The portable unit also contains signal processing components necessary to convert the GPS signal into location information and a remotely programmable memory database that receives and stores the desired boundary parameters. Circuitry within the portable unit compares the GPS defined location information with the predetermined parameters and activates an audible signal; and if necessary, an electrical shock will be delivered, when the collared animal approaches the defined boundary.[4]
Some disadvantages to invisible fencing include its inability to keep other animals out of this predetermined boundary.[5] A dog contained within an invisible fence can still fall prey to a larger dog or coyote, or even a person looking to harass or even steal animals. This type of fencing does not have a warning mechanism to humans who might inadvertently wander inside the perimeter, making them more susceptible to dog bites/attacks. This type of containment is also not maintenance free; this system can only operate if the batteries in the animal’s collar are properly working. Finally invisible fencing is not effectively accepted by every animal. Some pets become too afraid to wonder into their yards out of fear of being shocked.[5]
Traditional herding methods can be very-labor intensive and time consuming. Cattle graze over large paddocks (a fenced area, usually near a stable, chiefly used for cattle grazing); in a typical farm containing several paddocks, cattle are rotated frequently between these fields to prevent over-grazing in any one particular area.[2] Farm herders spend a significant amount of time to move cattle over long distances and often times through in-climate weather.
A GPS based invisible fence can be used to virtually herd cattle through the automatic and gradual shifting of the containment borders. Cattle react to their environment by being attracted to, or repelled from different features of their environment. Cattle can be repelled from geographic features such traditional fences, rivers, rocks etc.[2] and are attracted to other cattle for protection and to fulfill their innate desire to gather. Virtual cattle herders use various sounds that are transmitted to a RF receiving device located on a collar that emits sounds that may occur in nature such as a roaring tiger, a barking dog or a hissing snake, to move cows in a desired direction. Electric stimulation is only applied if movement in the desired direction has not been detected by a GPS location processor. The least amount of force needed to get an animal to change its location usually occurs when the collared animal is already in movement and not at rest; thereby making audible and/or electric stimuli to moving animals most efficient and the least stressful.[2]
In 2004, researchers from the Swedish University of Agricultural Sciences successfully trained cattle to approach a feed source in response to auditory signals. To help improve cow traffic in automated milking systems, these heifers would approach a feeder in response to a audible stimuli being emitted from a collar.[6]