Radiotelemetry system for continuously monitoring temperature in cows

Deep body temperature is an important index of the physiological status of an animal. A radiotelemetry system was developed to monitor continuously udder and body temperatures in cows under normal housing conditions. Radiotransmitters were crystal controlled blocking oscillators operating in the 27 MHz band. Functionally, the transmitters turned on and off in a pulsatile fashion with temperature encoded as the time interval between two pulses (nominally .5 s at 38 degrees C). Transmitters were powered by lithium batteries (6-mo lifespan) and were encapsulated in paraffin/Elvax (cylinder 6 cm X 3 cm diameter). Signals were detected using a radio receiver in the AM mode. Reception frequency was selected by computer. Each audio pulse was electronically converted to a digital pulse. A PDP 11/23 computer converted intervals between digital pulses to temperature values. As finally configured, the computer collected data from 12 transmitters every 1.4 min (1024 readings/transmitter/d). Temperatures were graphed continuously and stored on magnetic media for future analyses.