Fausnacht, Dane W.Kroscher, Kellie A.McMillan, Ryan P.Martello, Luciane S.Baumgard, Lance H.Selsby, Joshua T.Hulver, Matthew W.Rhoads, Robert P.2021-01-222021-01-222021-01-17Fausnacht, D.W.; Kroscher, K.A.; McMillan, R.P.; Martello, L.S.; Baumgard, L.H.; Selsby, J.T.; Hulver, M.W.; Rhoads, R.P. Heat Stress Reduces Metabolic Rate While Increasing Respiratory Exchange Ratio in Growing Pigs. Animals 2021, 11, 215.http://hdl.handle.net/10919/102016Heat stress (HS) diminishes animal production, reducing muscle growth and increasing adiposity, especially in swine. Excess heat creates a metabolic phenotype with limited lipid oxidation that relies on aerobic and anaerobic glycolysis as a predominant means of energy production, potentially reducing metabolic rate. To evaluate the effects of HS on substrate utilization and energy expenditure, crossbred barrows (15.2 ± 2.4 kg) were acclimatized for 5 days (22 °C), then treated with 5 days of TN (thermal neutral, 22 °C, <i>n</i> = 8) or HS (35 °C, <i>n</i> = 8). Pigs were fed ad libitum and monitored for respiratory rate (RR) and rectal temperature. Daily energy expenditure (DEE) and respiratory exchange ratio (RER, CO2:O2) were evaluated fasted in an enclosed chamber through indirect calorimetry. Muscle biopsies were obtained from the longissimus dorsi pre/post. HS increased temperature (39.2 ± 0.1 vs. 39.6 ± 0.1 °C, <i>p</i> < 0.01) and RER (0.91 ± 0.02 vs. 1.02 ± 0.02 VCO2:VO2, <i>p</i> < 0.01), but decreased DEE/BW (68.8 ± 1.7 vs. 49.7 ± 4.8 kcal/day/kg, <i>p</i> < 0.01) relative to TN. Weight gain (<i>p</i> = 0.80) and feed intake (<i>p</i> = 0.84) did not differ between HS and TN groups. HS decreased muscle metabolic flexibility (~33%, <i>p</i> = 0.01), but increased leucine oxidation (~35%, <i>p</i> = 0.02) compared to baseline values. These data demonstrate that HS disrupts substrate regulation and energy expenditure in growing pigs.application/pdfenCreative Commons Attribution 4.0 Internationalheat stresslipid oxidationenergy expenditurerespiratory exchange ratioHeat Stress Reduces Metabolic Rate While Increasing Respiratory Exchange Ratio in Growing PigsArticle - Refereed2021-01-22Animalshttps://doi.org/10.3390/ani11010215