Virtual fencing in remote boreal forests: performance of commercially available GPS collars for free-ranging cattle

BackgroundThe use of virtual fencing in cattle farming is beneficial due to its flexibility, not fragmenting the landscape or restricting access like physical fences. Using GPS (Global Positioning System) technology, virtual fence units emit an audible signal and a low-energy electric shock when crossing a predefined border. In large remote grazing areas and complex terrains, where the performance of the GPS units can be affected by landscape structure, increased positioning errors can lead to unnecessary shocks to the animals leading to animal welfare concerns. This study aimed to explore factors affecting the GPS performance of commercially available virtual fence collars for cattle (NoFence (c)), both using static tests and mobile tests, i.e., when deployed on free-ranging cattle.ResultsThe static tests revealed generally high fix success rates (% successful positioning attempts), and a lower success rate at four of 30 test locations was most likely due to a lack in GSM (Global System for Mobile communications) coverage. On average the GPS precision and accuracy errors were 3.3 m +/- 2.5 SD and 4.6 m +/- 3.2 SD, respectively. We found strong evidence that the GPS precision and accuracy errors increased errors under closed canopies. We also found evidence for an effect of the sky-view on the GPS performance, although at a lesser extent than canopy. The direction of the accuracy error in the Cartesian plane was not uniform, but biased, depending on the aspect of the test locations. With an average of 10.8 m +/- 6.8 SD, the accuracy error of the mobile tests was more than double that of the static tests. Furthermore, we found evidence that more rugged landscapes resulted in higher GPS accuracy errors. However, the error from mobile tests was not affected by canopy cover, sky-view, or cattle behaviors.ConclusionsThis study showed that GPS performance can be negatively affected by landscape complexity, such as increased ruggedness and covered habitats, resulting in reduced virtual fence effectiveness and potential welfare concerns for cattle. These issues can be mitigated through proper pasture planning, such as avoiding rugged areas for the virtual fence border.