Virtual fencing is a method of controlling animals without ground-based fencing. Control occurs by altering an animal’s behaviour through one or more sensory cues administered to the animal after it has attempted to penetrate an electronically-generated boundary. This boundary can be of any geometrical shape, and though unseen by the eye, is detected by a computer system worn by the animal. The most recent autonomous programmable systems use radio frequency (RF) signals, emanating from global positioning system (GPS) satellites to generate boundaries. Algorithms within a geographic information system (GIS) within the device’s computer use the GPS and other data to determine where on the animal a cue, or cues, should be applied and for how long. The first commercial virtual fencing system was patented in 1973 for controlling domestic dogs. Virtual fencing was used for the first time to control livestock in 1987. Since then proof-of-concept research using commercial, as well as custom designed systems have demonstrated that virtual fencing can successfully hold as well as move livestock over the landscape. Commercial virtual livestock control systems do not yet exist but research continues towards this goal. Pending research needs relating to this method of animal control are discussed in light of currently available technologies.

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Perennial shortgrasses were delayed in responding to removal of a dense broom snakeweed population (387/m') because of low initial vigor. However, after 1 year, grass production increased by 107% (1,175 kg/ha) and after 2 years, by 324% (2,201 kg/ha) compared to undisturbed stands. Reducing snakeweed density by 25 or 50% did not affect forage production during the ,2-year study. Estimated carrying capacity of the shortgrass rangeland was increased from 1 A.U./26 ha to 1 A.U./6.1 ha by the second year after complete removal of broom snakeweed. Juvenile broom snakeweed plants utilized soil water from the upper 15 to 45 cm. Soil water depletion was increased after perennial grasses regained vigor following complete removal of snakeweeds. Precipitation-use efficiency for production of usable forage was 2.1 and 4.3 times greater on broom snakeweed-free rangeland than on infested rangeland at 1 and 2 years, respectively, following removal of snakeweed.

We examined the effects of six volatile compounds on alfalfa pellet consumption by lambs. In each experiment, 45 lambs were individually fed alfalfa pellets sprayed with a selected compound (camphor, limonene, cis-jasmone, beta-caryophyllene, borneol, or alpha-pinene) at one of five concentrations. Treatment concentrations were multiples (0, .5, 1, 2, and 10) of the concentration of a specific compound (X) that was related to differential herbivory of tarbush by livestock in previous studies. Treatments were applied to alfalfa pellets (.64 kg x lamb(-1) x d(-1), DM basis), and consumption was measured during a 20-min interval each morning for 5 d. Lambs were adapted to handling procedures and the pelleted diet (without treatments) for 10 d. Lambs were maintained and fed (approximately 4.5 to 5% of BW) as one group except during 20-min tests. A negative linear effect of treatment concentration on intake was observed for camphor (P < .02) and alpha-pinene (P < .01), and a quadratic response was detected for borneol (P < .02). The other three compounds had no discernible effect on consumption. Although volatile compounds generally had only minor influences on consumption, the negative influences of alpha-pinene and camphor concentrations on pellet consumption suggest that these monoterpenes may partially explain differential herbivory of individual tarbush plants by livestock.

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