A method of monitoring an animal, comprising the steps of: a) orally administering to a ruminant animal a monitoring device (6) and a first magnet (85) contained inside of an inert bolus body (4), said animal monitoring device including: i) at least one sensor (9) capable of generating a signal which varies in relation to change in a sensed animal characteristic； ii) a signal encoder (68) which encodes said signal generated by said sensor as encoded sensed animal characteristic information； iii) a radio frequency signal generator (81) which generates a radio frequency signal (12) capable of carrying said encoded sensed animal characteristic information； iv) a power source (84) which supplies power to said animal monitoring device； and v) an antenna (83) capable of transmitting said radio frequency signal carrying said encoded sensed animal characteristic information； and b) accessing said encoded sensed animal characteristic information carried by said radio frequency signal.
