Effect of environmental conditions on growing pig weight (A), feed intake (B), respiratory rate (C), rectal temperature (D). Correlation of daily energy expenditure (DEE) to animal body weight and energy intake (E). Indirect calorimetry measures on growing pigs of respiratory exchange ratio (RER) (F), DEE (G), and DEE per body weight (BW) (H). 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 (Pre). 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 (Post). Means without a shared letter are significantly different, p < 0.05.