摘要In the present study,the chronic heat stress(CHS)broiler model was developed to investigate the po-tential protection mechanism of organic selenium(selenomethionine,SeMet)on CHS-induced skeletal muscle growth retardation and poor meat quality.Four hundred Arbor Acres male broilers(680±70 g,21 d old)were grouped into 5 treatments with 8 replicates of 10 broilers per replicate.Broilers in the control group were raised in a thermoneutral environment(22±2 ℃)and fed with a basal diet.The other four treatments were exposed to hyperthermic conditions(33±2 ℃,24 h in each day)and fed on the basal diet supplied with SeMet at 0.0,0.2,0.4,and 0.6 mg Se/kg,respectively,for 21 d.Results showed that CHS reduced(P＜0.05)the growth performance,decreased(P＜0.05)the breast muscle weight and impaired the meat quality of breast muscle in broilers.CHS induced protein metabolic disorder in breast muscle,which increased(P＜0.05)the expression of caspase 3,caspase 8,caspase 9 and ubiquitin proteasome system related genes,while decreased the protein expression of P-4EBP1.CHS also decreased the antioxidant capacity and induced mitochondrial stress and endoplasmic reticulum(ER)stress in breast muscle,which increased(P＜0.05)the ROS levels,decreased the concentration of ATP,increased the protein expression of HSP60 and CLPX,and increased(P＜0.05)the expression of ER stress bio-markers.Dietary SeMet supplementation linearly increased(P＜0.05)breast muscle Se concentration and exhibited protective effects via up-regulating the expression of the selenotranscriptome and several key selenoproteins,which increased(P＜0.05)body weight,improved meat quality,enhanced antiox-idant capacity and mitigated mitochondrial stress and ER stress.What's more,SeMet suppressed protein degradation and improved protein biosynthesis though inhibiting the caspase and ubiquitin proteasome system and promoting the mTOR-4EBP1 pathway.In conclusion,dietary SeMet supplementation in-creases the expression of several key selenoproteins,alleviates mitochondrial dysfunction and ER stress,improves protein biosynthesis,suppresses protein degradation,thus increases the body weight and improves meat quality of broilers exposed to CHS.