## 4 Discussion
If the VIT of Brand 2 was expelled during the middle of the day, the outside temperature may have been above the 34 \({}^{\circ}\)C threshold and solar radiation could also have contributed to maintaining high temperature of the VIT, as seen in the reported data with values above 60 \({}^{\circ}\)C which would not allow the alert to be triggered. The vaginal temperature was on average 38.66 \({}^{\circ}\)C, with the lowest recorded at 37.13 \({}^{\circ}\)C compared to the maximum ambient daily temperatures during the calving season months of 35.6 \({}^{\circ}\)C in Trial 1 and 37.0 \({}^{\circ}\)C in Trial 2 [18]. Therefore, the temperature of the expelled VIT may not reach the threshold required fast enough to trigger an alert for either brand resulting in a missed alert. Ambient temperature was shown to have an impact on VIT, emitting an expulsion pulse in a study using VIT in deer [31]. It showed that the probability of VIT emitting an expulsion alert declined as ambient temperature rose, with almost zero probability of an expulsion alert if temperatures were above 35 \({}^{\circ}\)C, however this fluctuated slightly, depending on vegetation type and shade or sun exposure [31]. A false alert could be triggered when a cow remained inactive for over an hour and reached the required temperature threshold, despite not expelling the VIT. However, the VIT temperature data demonstrated that this had not occurred in this trial. The time between VIT expulsion and receiving the birth alert notification varied greatly with up to 12 and 18-h delay. In these cases, cows travelled around 700 m between the expelled alert time and email notification, showing the challenges in reaching cows and calves in an extensive system after receiving a birth alert. This time lapse could be due to poor connection between the collar and the satellites, caused by tree cover, rocky or hilly terrain, thereby causing a delay. The greater the time lapse between calving or VIT expulsion and attendance to the birth site, the less likely it was to find the calf for data recording. Furthermore, the time of the VIT expulsion in relation to the time of calf expulsion is unknown and further research is required to determine this. Overcoming limitations of the time required for the satellite communications would require a change to communication protocols such as the use of LoRaWAN (Long Range) [37] or low-power wide-area network (LPWAN) [38]. The distance travelled by cows decreased during the first few days after calving in Trial 2, but not in Trial 1, which could have been a result of animals in Trial 2 being in a smaller paddock (7 km\({}^{2}\)) compared to animals in Trial 1 (33 km\({}^{2}\)). This is the first study assessing cow movements around calving time in extensive commercial systems. The high activity of cows on the day of and after calving observed could be due to increased alertness of cows and need to continuously move to avoid calf predation by wild dogs [39], which were regularly seen during the calving season, and also the need to attend the water point to drink, abandoning the calving site. These findings highlight the limitations of VIT to satellite communication technology in detecting birthing events for animal species that move large distances after birth. With cows remaining mobile after birth, this may have impacted the communication between the collar and the VIT due to the limited time the collar and VIT were in close proximity to communicate via UHF and send a birth alert. Therefore, a reduction in the inactivity threshold to trigger the birth alerts is recommended although this could increase the false birth alert rate. Tracking the VIT and the collared cows after expulsion in the field was challenging. This was partly due to the terrain, vegetation and size of the paddock, but also the limited range, or strength of the VIT signal to reach the VHF tracker, a limitation also noted by [PERSON] et al. [40].