Technical Abstract: Respiration rates (RR) were included as one measure in studies investigating bioenergetic responses of cattle to heat challenges. Separate studies considered RR as one response measure in growing-finishing swine exposed to adverse thermal environments. Both studies incorporated RR monitors using small battery powered micro-computers and specially adapted sensors to log RR data. This paper reports the development of the monitors and the relevance of the data as an indicator of stress for both cattle and swine. Characteristic cattle data obtained in environmental chambers and from a field study, as well as representative swine data from a calorimetry study, all indicate an association of RR and ambient temperature (P<0.01). Data reduction and analysis are also discussed, based on representative samples of records collected.