Effects of dietary threonine and arginine on growth performance, stress indicators, and gut health in broiler chickens under multiple stress

8 This study evaluated the effects of dietary threonine (Thr) and arginine (Arg) concentrations on 9 growth performance, meat quality, stress indicators , antioxidant capacity, and gut health in 10 broiler chickens raised under multiple stress conditions. A total of 280 21-d-old broiler chickens 11 were randomly allotted to 4 treatments with 8 replicates. The positive control (PC) group was 12 raised under normal rearing conditions (thermoneutral temperature and low stocking density; 13 22.6 ± 0.6°C for 24 h and 15.2 birds/m 2), whereas the remaining groups were subjected to 14 multiple stress conditions (cyclic heat stress and high stocking density; 29.3 ± 0.9°C for 10 h, 15 22.8 ± 0.8°C for 14 h, and 30.3 birds/m 2). Both t he PC and negative control (NC) groups 16 received a basal diet, while the other two groups were provided diets containing 1.3-fold higher 17 concentrations of digestible Thr or Arg compared to the basal diet. Experimental diets and water 18 were supplied ad libitum for 14 d. Results indicated that growth performance was decreased (p 19 < 0.05) in NC, Thr, and Arg groups compared to PC group. Birds in NC group had greater (p < 20 0.05) heterophil to lymphocyte ratio and feather corticosterone (CORT) concentrations than 21 those in PC group. Under multiple stress conditions, Thr and Arg groups showed less (p < 0.05) 22 feather CORT concentrations than NC group. In hepatic tissue, reactive oxygen species levels 23 were increased ( p < 0.05) in NC and Arg groups compared to PC group. Jejunal nitric oxide 24 levels were increased ( p < 0.05) in NC group compared to PC, Thr, and Arg groups. Under 25 multiple stress, Thr and Arg treatment groups exhibited greater ( p < 0.05) transepithelial 26 electrical resistance values than NC group. The expression levels of OCLN, ZO-1, and HSP70 27 were greater (p < 0.05) in Thr and Arg groups than in NC group. In conclusion, increasing 28 dietary concentrations of Thr and Arg improves intestinal integrity and mitigates stress response 29 in broiler chickens exposed to multiple stress. 30 31