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Researchers and producers alike have noted the increased susceptibility to heat stress exhibited by the newer genetic lines of pigs. A study was conducted to gather baseline information on the effects of acute heat stress on total heat production (THP), respiratory quotient (RQ), respiration rate (RR), and rectal temperature (Trectal ) and to investigate the dynamic interaction of these parameters in growing–finishing barrows. Sixteen moderate–lean growth barrows were randomly assigned to a set of treatments as dictated by a repeated 4x4 Latin square crossover design. Pigs were moved from an individual pen to an indirect calorimeter where one of four environmental treatments (18, 24, 28, 32°C) were applied for 20 h. During the treatment exposure RR, THP, RQ and Trectal were measured. For the 2-week period between treatments, pigs were housed at thermoneutral (22°C). THP was found to be 17–20% higher than the published standards but comparable with other contemporary studies. Respiration rate was found to be a leading indicator of stress.