Investigation of Bluetooth Low Energy (BLE) as a precision livestock farming tool in grazing sheep systems

Walker, Aimee May (2025) Investigation of Bluetooth Low Energy (BLE) as a precision livestock farming tool in grazing sheep systems. PhD thesis, University of Glasgow.

Abstract

The livestock industry has seen substantial growth in the development and availability of technologies and tools in recent decades. These precision livestock farming (PLF) technologies can be employed by farmers to monitor an array of behavioural, physiological, and environmental variables to assist in production and welfare management. Benefits of employing such tools have been demonstrated within intensive farming systems, such as pig and poultry, and for dairy cattle, where PLF tools have seen the greatest adoption. However, the uptake of tools for species considered to have a lower economic value, such as domestic sheep (Ovis aries), has been slower, especially in grazing systems where fewer technologies have been developed, validated, and made commercially available. The incorporation of PLF tools within grazing systems can be more complex given the potential scale of farms, flock sizes, and dispersion of animals over wide areas, which can create challenges in transmitting information. Given the fairly small physical size of sheep compared to cattle, there is also a requirement for devices to be robust, lightweight, and cost-effective.

Bluetooth low energy (BLE) is a rapidly growing technology which has expanded across multiple sectors in recent years, predominantly for location and proximity monitoring. As a low-cost, low-power device, with long-battery life, and suitable for use in outdoor conditions, it offers promising potential as PLF tool in sheep grazing systems. Whilst animals in extensive systems are generally considered to have more behavioural freedom than those in intensive systems, they are exposed to greater environmental challenges. The ability to monitor animal location, proximity and relationships over time could provide useful information for both production and welfare aspects of sheep management. However, the signal strength of BLE devices can be noisy, and further information is needed to understand the relationship between signal strength and distance within an outdoor environment to assess the ability of BLE to act as on-sheep monitoring tool.

A prototype BLE system was developed for the thesis, consisting of a purpose-built device with BLE reader, trialled alongside three types of commercially available BLE beacons. The main aims of the thesis were (1) to characterise the relationship between BLE signal strength and distance, and to assess the range of BLE in outdoor systems, (2) to assess the application of BLE for sheep localisation in grazing systems, and (3) to investigate the capability of BLE to be utilised as a monitoring tool to detect sheep contact patterns and relationships, and changes over time - which may indicate a potential welfare or management problem.

Calibration studies of the three beacon types were conducted within a field environment to explore how signal strength changed with distance and whether this was affected by device height and thus animal behaviour. From these calibrations, distance prediction equations based on signal strength were developed. The potential impact of sheep bodies on the signal strength and operating range was assessed for two of the beacon types by conducting calibrations under both a clear and blocked line-of-sight. Across all beacon types, signal strength declined with increasing beacon distance from a reader, with reduced ranges at lower reader and beacon heights. An on-sheep study, with corresponding observer data, demonstrated that animal behaviour, thus posture and height of the BLE device from the ground also impacted on both the beacon’s probability of being reported and its signal strength. This showed that operating ranges and translation of signal strength into a distance is then highly dependent upon the behaviours displayed by sheep during a recording interval.

BLE was also trialled as a means of localisation within a grazing system. A static multilateration approach was tested in a paddock (approximately 5 440 m2) using six BLE readers, followed by an on-sheep validation in the localisation of a weaned lamb, fitted with both a BLE beacon and separate global navigation satellite system (GNSS) device, within a larger paddock (1.4 ha), surrounded by nine BLE readers. In the static approach, the multilateration method produced a mean localisation error of 22.02 m, with the on-sheep validation producing similar mean localisation errors – 19.00 m using a midpoint method, and 23.77 m using the multilateration method. Whilst the studies demonstrated the technical feasibility of localising sheep in an outdoor system using BLE, it also highlighted that interpretation of signal strength into distance can be unpredictable, particularly in relation to animal behaviour and movement. Based on the range of BLE devices tested, a high number of static readers would also be required to adequately cover a grazing system. Substantial development in BLE range and accuracy would then be required for any viable commercial application of such a system.

Finally, an on-sheep study examined the use of the BLE system as a monitoring tool, conducted during the high activity period of lambing and early lactation. Lamb mortality and poor ewe-lamb relationships remain a top welfare and economic concern, with high numbers of lamb losses occurring between birth and weaning. Using the purpose-built device as an on animal device worn by ewes (also fitted with a BLE beacon) alongside BLE beacons on lambs, ewe-ewe and ewe-lamb relationships were assessed across pre- to post-lambing phases, and in relation to lamb age over a six-week period. The BLE system successfully detected and demonstrated expected patterns in ewe and lamb relationships. The numbers of ewe-ewe contacts reported within a 5-minute duty cycle was found to decline between pre-lambing to lambing, and lambing to post-lambing, suggestive of segregation at parturition. The pattern in the number of daily ewe-lamb contacts changed across increasing lamb ages. Whilst initially reporting a high number of contacts, this gradually declined until approximately 14 days old, a period during which lambs typically begin to spend more time within peer groups. The number of contacts was also assessed in relation to ewe lameness, with the BLE system
indicating a reduction in contacts with neighbouring ewes, and an increase in contacts with their own lambs. As lame ewes are more inactive, then it may be easier for lambs to remain in closer proximity.

To conclude, the investigations within this thesis trialled a BLE system for the purposes of animal monitoring within a sheep grazing system. Calibration studies identified challenges in the detection of BLE signals and translation into distance, which can be affected by device height, animal behaviour and orientation. The potential operating ranges and extent to which signal strength can provide useful information may then limit BLE application in some scenarios as this will be highly affected by animal behaviour. However, the BLE system did demonstrated potential in identifying contact patterns and relationships amongst ewes and lambs, which could be used to monitor and identify both positive ewe-lamb relationships, as well as potential issues if ewe-lamb contacts deviated from an expected range based on the lambs age and breed. Adding BLE to a suite of sensors and data streams could potentially enhance and complement findings from this thesis.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from 862050 (European Union’s Horizon 2020 Research and Innovation Program).
• Subjects: S Agriculture > SF Animal culture > SF600 Veterinary Medicine
• Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Biodiversity Animal Health and Comparative Medicine
• Funder's Name: European Union’s Horizon 2020 Research and Innovation Program
• Supervisor's Name: Jonsson, Professor Nicholas and Morgan-Davies, Dr. Claire
• Date of Award: 2025
• Depositing User: Theses Team
• Unique ID: glathesis:2025-85318
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 17 Jul 2025 14:59
• Last Modified: 17 Jul 2025 15:03
• URI: https://theses.gla.ac.uk/id/eprint/85318

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