Generally, an animal monitoring system including a bolus administered to reside in an animal operable to sense changes in one or more physiological parameters of the animal and generate and transmit encoded bolus sensor data to a tag affixed on the outside of the animal which operates to sense changes in one or more environmental parameters surrounding the animal and to generate encoded tag sensor data and to receive encoded bolus sensor data each of which can be analyzed by the tag or a remote data processor to generate environmental parameter values and physiological parameter values to assess an environmental or physiological condition of or about the animal.