Potential for automatic oestrus detection in grazing cattle through the integration of Global Navigation Satellite System tracking and Bluetooth proximity logging

Achieving a profitable and sustainable beef cattle operation requires an appropriate reproductive management. Oestrus detection is essential for optimising artificial insemination and/or identifying non-performing cows, amongst other benefits. Traditionally, oestrus detection has relied on visual observation, but this practice poses several challenges, particularly in extensive grazing systems. The aim of this study was to evaluate a sensor system combining GNSS tracking and Bluetooth proximity logging, based on signal strength, to automatically detect oestrus in grazing cows. Fifty-three heifers and three sires were fitted with GNSS collars and Bluetooth ear tags, respectively, and several oestrus indicators were calculated from the data collected by sensors over a period of ten weeks. These indicators included the number of cow-sire proximity records, the signal strength of these records, the time interval between successive records and the spatial characteristics of cow-sire interactions. Several indicators showed significant differences between the day of oestrus and the 14 days before and after oestrus. The number of cow-sire proximity interactions recorded by the system tripled on the day of oestrus. Minimum value of signal strength indicator and time between successive records for the same cow were lower on the day of oestrus. The trajectories defined by the GNSS coordinates of the sire(s) when recording cow proximity were longer (distance and duration) and tended to be less straight on the day of oestrus. A tendency to explore a greater area on the day of oestrus was also observed. The time resolution of data provided by sensors (30-min epochs) may prevent the identification of significant differences in some of the studied indicators. Also, the effects of cow-to-sire ratio and paddock configuration deserve further investigation. Nevertheless, the integration of data from GNSS tracking and Bluetooth proximity logging proved to be useful for the detection of oestrus in grazing cattle.