I believe that BLE (Bluetooth Low Energy/Bluetooth 4.2) can be very handy for animals that are kept in relatively small areas (E.g. dairy cows) as well as for animals that roam large areas (E.g. field grazing sheep/cattle). 

For animals in confined areas BLE can be used to transfer all data and since they should always be close to a base station. Since all smartphones and tablets are equipped with BLE it allows interfacing with individual tags directly without special equipment.

For roaming animals the applications for BLE gets more interesting. Since cattle, sheep, and goats tend to move in herds, BLE advertising and/or Bluetooth Mesh can be used to monitor herd behavior. The different tags in a group equipped with GPS can take turns to fix locations, so that the power consumption for each individual tag is kept to a minimum while still maintaining an accurate fix on the herd as a whole.

When an individual animal or group breaks off from the herd, it can be quickly determined by checking which animals are still within BLE range of each other and adapt the GPS usage accordingly. GPS usage can be even further reduced by placing BLE beacons in fixed locations to track animal movement.

For these reasons I plan to use BLE enabled MCU’s as the base for all future versions of this project. I will also be looking at Bluetooth 5 capable modules to allow upgrading as time goes on and it becomes more widely implemented.