Effect Of Heat Stress On Meat Quality Of Broilers Breast Muscle And Its Mechanism

Under the trend of global increasing temperatures and the poultry to intensive development,heat stress has become a common problem in poultry raising,which has a certain impact on the meat quality.Although it is an indisputable fact that heat stress can cause the meat quality of birds to decline,the intrinsic mechanism of heat stress affecting meat quality needs further study.It is hoped that this experiment can provide new ideas and theoretical basis for the research on the regulation mechanism of stress-induced meat quality and the development and application of antioxidant additives.After the 35-day-old AA broilers were respectively fed for 2h and 4h in the control(23?)and high temperature hot environment(29? and 35?),the relative weight of broiler heart,liver and spleen is measured.Meat quality-related serum indicators alkaline phosphatase(AKP)and creatine kinase(CK)activity were measured,the development of muscle fibers was observed.At the same time,the changes of relative antioxidant enzyme activities and lipid peroxidation products in breast muscle were compared.And the expression of nuclear factor erythroid 2-related factor 2(Nrf2)and toll-like receptor 4(TLR4)genes in the pectoral muscle was further analyzed.The results showed as follows:1.Heat stress reduced the relative weight of heart,liver and spleen,decreased the content of AKP in serum and increased the content of CK,caused pathological changes such as muscle bundle boundaries blurring and the gap of muscle fibers increasing and irregular arrangement,and decreased the cross-sectional area of muscle fiber.2.The activity of glutathione peroxidase(GSH-PX),total superoxide dismutase(T-SOD)and total antioxidant capability(T-AOC)decreased significantly in the pectoral muscle of the broilers that were exposed to heat stress,but the content of malondialdehyde(MDA)increased with the extension of heat stress time.3.Further,the detection results that the gene expression level of Nrf2 and TLR4 m RNA related to the oxidative stress of pectoral muscle indicated the expression of Nrf2 m RNA decreased with the rise of temperature in the pectoral muscle of broilers exposed to heat stress for 2h.But the expression of Nrf2 m RNA increased with the rise of temperature when broilers were exposed to heat stress for 4h.The expression level of TLR4 m RNA increased with the increase of stress temperature in the pectoral muscle.In conclusion,heat stress delays the development of the broiler heart,liver and spleen,meat quality in the pectoral muscle declines by influencing the development of muscle fibers and inducing oxidative stress.And Nrf2 and TLR4 play an important role in the process of heat stress affecting meat quality.