Effects of heat stress on antioxidant capacity and gastrocnemius musclefiber types of broilers

Objective The present study was conducted to investigate the effects of chronic heat stress on antioxidant capacity, endoplasmic reticulum stress and gastrocnemius muscle fiber types of yellow feather broilers.

Method Twenty 47-day-old yellow feather broilers were randomly divided into control and chronic heat stress groups with 10 broilers in each group. The broilers were raised in an artificial climate chamber for 30 days. At the end of the trial, the samples of blood, liver and gastrocnemius muscle were collected. Serum biochemical indexes, hormones and antioxidant indexes of liver and gastrocnemius muscle were determined using the commerical assay kit method. And the mRNA expression of endoplasmic reticulum stress (ERS) related genes and myosin heavy chain (MyHC) of different skeletal muscle fiber types were detected using real-time quantitative PCR.

Result and conclusion Chronic heat stress significantly (P < 0.05) decreased the average daily gain, serum TG content, thyroid hormone (T₃ and T₄), and insulin-like growth factor 1 (IGF-1) levels, and increased serum corticosterone (CORT) concentration. Meanwhile, chronic heat stress markedly (P < 0.05) enhanced serum malondialdehyde (MDA) content, and reduced serum, GSH-PX activity and total antioxidant capacity (T-AOC) in liver.In addition, chronic heat stress remarkablly (P < 0.05) elevated the mRNA expression of heat shock protein 70 (HSP70) in liver and gastrocnemius muscle, and of activating transcription factor 4 (ATF4) in gastrocnemius muscle, and decreased the glucose-regulated protein 78 (GRP78) mRNA expression in gastrocnemius muscle, with no obvious effect on the mRNA expression of ATF4 and GRP78 in liver. Moreover, chronic heat stress significantly (P < 0.05) inhibited the mRNA expression of slow myofiber MyHC, with no influence on MyHC mRNA expression of fast red myofiber and fast white myofiber. In conclusion, this results suggest that chronic heat stress may affect broiler growth and gastrocnemius muscle fiber types by decreasing serum hormones involved in growth and metabolism, antioxidant capacity and eliciting ERS.