# May the Extensive Farming System of Small Ruminants Be Smart?
## 3 Results
### Wearable Sensors
#### 3.2.5 Virtual Fencing  
Virtual fencing (VF) technology is an innovative method for extensive animal management that replaces physical barriers with electronically placed boundaries. Animals are prevented from passage by a system of visible and/or audible cues combined with an electric stimulus: when the animal approaches the virtual fence, the collar emits a warning signal, usually a sound. A painful but harmless electric shock is given if the animal moves forward and is about to cross the fence line. Recent studies have shown that animal welfare in virtual fences is comparable to that in a physical electric fence and that cattle and sheep can learn to respond to audio signals and avoid electrical impulses [24; 28]. The position of the virtual border can be defined by coordinates, GPS, or satellite signals or by a ground cable that communicates with the collars. The main species were tested in different virtual fencing systems: cattle [26; 28], sheep [27; 62; 63], and goats [15]. Studies have demonstrated different responses in species and with varying systems of monitoring [64]. The multiple animal monitoring capabilities allowed by VF collars (rest time, distance travelled, and spatial distribution) represent a further key advantage of this technology, highlighting the potential of precision breeding (Table 1). [PERSON] et al. [64] have shown that the application of VF collars and other sensors for monitoring grazing animals provides precise position indications, and by monitoring grazing from above using Unmanned Aerial Vehicle (UVA) technology, it is possible to improve grazing systems, as it predicts the biomass changes across animal data. [PERSON] et al. [28] tested the use of the Nofence(r) system to keep a group of Angus cattle (Bos taurus) inside a virtual fence with minimal welfare implications, i.e., without harming livestock welfare, basic health, and functioning. [PERSON] et al. [27] demonstrated that sheep could quickly associate audio cues with the electrical stimulus, and the ewes efficiently adapted to a second virtual boundary, indicating that they generalized their experiences from the first to the second boundary. These findings are important for animal welfare, as noted in the heart rate response to the electric stimulus, indicating a brief stress reaction. The sheep species adapts easily to the audio signal, as reported by [PERSON] et al. [62], and can learn to associate the sound signal with the electric shock and, therefore, after a learning period, at least in some cases, will remain on one side of the virtual fence. [PERSON] et al. [63] managed to keep a group of sheep in a virtual pen for five days. However, several studies have reported that some animals cross the virtual border. A word cloud of the primary wearable devices and applications in sheep extensive farming systems is shown in Figure 1.  
Figure 1: Word cloud of the main wearable devices and their applications in sheep extensive farming systems (in blue and black are shown the device positions; in red and green are shown the recorded parameters).  
The font sizes of individual words correlate positively with the number of searches on each specific device.