Heat stress increases respiratory exchange ratio while reducing daily energy expenditure in growing pigs

• Published in: The FASEB journal 2020-04, Vol.34 (S1), p.1-1
• Main Authors: Fausnacht, Dane, Kroscher, Kellie Ann, Selsby, Joshua T., Baumgard, Lance H., Rhoads, Robert Paul
• Format: Article
• Language: English
• ISSN: 0892-6638; 1530-6860
• DOI: 10.1096/fasebj.2020.34.s1.02440

Abstract only Heat stress (HS) alters animal metabolism causing reduced performance (muscle growth) while increasing the incidence of disease and mortality. HS is particularly detrimental in the swine industry where the global economic burden of heat stress is in the billions of dollars annually. Excess environmental heat promotes a HS response increasing the expression of heat shock factors and heat shock proteins which coordinate a shift in metabolic substrate preference. The net result of these changes is a metabolic phenotype with limited lipid oxidation that relies on aerobic and anaerobic glycolysis as a predominant source of energy production. This study was designed to evaluate the effect of HS on substrate utilization and overall animal metabolic rate in growing pigs. Crossbred barrows (15.2±2.4 kg) were exposed to 5 days of TN (thermal neutral, 24 C°) or HS ( 35 C°) (n=8 per treatment), after a 5‐day acclimation period (24 C°). Pigs were fed ad libitum and monitored regularly for respiratory rate (RR) and rectal temperature (3x daily). A metabolic cart was used to assess daily energy expenditure (DEE), and respiratory exchange ratio (RER, CO2:O2), pigs were placed in an enclosed chamber and gas exchange was measured for 1 hour after a 30 min washout. Muscle biopsies were taken from the longissimus dorsi to evaluated palmitate, pyruvate, and leucine oxidation capacity and metabolic flexibility (metflex). Metabolic measures and muscle biopsies were taken after five days of acclimation (pre) and immediately following (post) the 5‐day environmental treatments. Initial DEE was positively correlated to weight (r 2 =0.55, p