Heat Stress Reduces Metabolic Rate While Increasing Respiratory Exchange Ratio in Growing Pigs

• Published in: Animals (Basel) Vol. 11; no. 1; p. 215
• Main Authors: Fausnacht, Dane W, Kroscher, Kellie A, McMillan, Ryan P, Martello, Luciane S, Davy, Kevin P, Baumgard, Lance H, Selsby, Joshua T, Hulver, Matthew W, Rhoads, Robert P
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.01.2021; MDPI
• Subjects: Acclimatization; Adipose tissue; Animal production; Biopsy; Calorimetry; Carbohydrates; Carbon dioxide; Cellular stress response; Energy; Energy expenditure; Environmental factors; Fatty acids; Feeds; Flexibility; Glycolysis; Heat; Heat stress; Heat tolerance; Hogs; Humidity; Hypertrophy; Leucine; Lipid metabolism; lipid oxidation; Lipid peroxidation; Lipids; Livestock; Metabolic rate; Metabolism; Metabolites; Muscles; Musculoskeletal system; Oxidation; Phenotypes; Random variables; Respiration; respiratory exchange ratio; Respiratory rate; Substrates; Swine; Temperature; United States > US; heat stress; lipid oxidation; respiratory exchange ratio; energy expenditure
• ISSN: 2076-2615; 2076-2615
• DOI: 10.3390/ani11010215

Heat 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, = 8) or HS (35 °C, = 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, < 0.01) and RER (0.91 ± 0.02 vs. 1.02 ± 0.02 VCO2:VO2, < 0.01), but decreased DEE/BW (68.8 ± 1.7 vs. 49.7 ± 4.8 kcal/day/kg, < 0.01) relative to TN. Weight gain ( = 0.80) and feed intake ( = 0.84) did not differ between HS and TN groups. HS decreased muscle metabolic flexibility (~33%, = 0.01), but increased leucine oxidation (~35%, = 0.02) compared to baseline values. These data demonstrate that HS disrupts substrate regulation and energy expenditure in growing pigs.