Relationship of daily energy expenditure (DEE) per bodyweight (BW) (post treatment, (A), and effect of treatment (B) compared to animal growth rates after 5 days of heat stress (HS)). Relationship of daily energy expenditure (C), daily energy expenditure per bodyweight (D) and growth rate (E) compared to change in rectal temperature during days after HS. Changes in RER after 5 days of HS or thermal neutral environmental treatments compared to average rectal temperature during treatment (F). Pigs were acclimated under thermoneutral conditions (14 h light/10 h dark, 21.6 ± 0.8 °C, with humidity 46–64%) for five days prior to treatment. Pigs were then randomly assigned (n = 8 per group) to thermal neutral (TN, 22.0 ± 0.4 °C, with humidity 43–63%) or heat stress (HS, 33.6 ± 0.5 °C, with humidity 22–40%) treatment groups for five days.