Studies were conducted investigating bioenergetic responses of growing cattle to heat challenges using respiration rate as one of the primary measures. Respiration rate (RR) was measured using monitors designed from commercially available thin-film pressure sensors and a small battery powered micro-computer. The monitors were designed, fabricated, and tested to provide continuous records as a basis for evaluating stress responses associated with environmental conditions. This article provides details about the monitors and the suitability of obtained records as an indicator of stress, based on measures obtained in environmental chambers during constant and simulated heat wave conditions as well as a field study. Representative data from two laboratory studies indicated an association of RR and ambient temperature (P < 0.01) with diurnal changes being evident in the cyclic test and step changes being evident in the constant ambient temperature tests. A two to three breaths per minute (BPM) rate of change of RR with respect to ambient temperature (℃) was observed for steers in the laboratory studies. The field study revealed a striking response of RR to the ambient temperature (6.6 BPM/℃ rate of change) for a steer that had direct solar load (no-shade) compared to a 1.6 BPM/℃ rate of change in the shade.
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