Abstract
Heat stress impairs growth performance and alters body protein and amino acid metabolism. This study was investigated to explore how body protein and amino acid metabolism changed under heat stress (HS) and the stress adaptation mechanism. A total of 144 broilers (28 d old) were divided into 3 treatment groups for 1 wk: HS group (32°C), normal control group (22°C), and pair-feeding group (22°C). We found that HS elevated the feed-to-gain ratio, reduced the ADFI and ADG, decreased breast muscle mass and plasma levels of several amino acids (glycine, lysine, threonine, and tyrosine), and increased serum glutamic oxaloacetic transaminase (GOT) activity and corticosterone (CORT) level and liver GOT and glutamic pyruvic transaminase activities. Heat stress elevated muscle atrophy F-box mRNA expression and reduced mRNA expression of the 70-kD ribosomal protein S6 kinase in the breast muscle of broilers. Broilers in the HS group exhibited striking increases of mRNA expressions of solute carrier family 1 member 1, family 3 member 1, family 7 member 1, and family 7 member-like in the liver and liver gluconeogenesis genes (PCKc, PCKm, PC, and FBP1) in comparison with the other 2 groups. In conclusion, HS increased the circulating CORT level and subsequently caused muscle protein breakdown to provide amino acid substrates to liver gluconeogenesis responsible for energy supply.