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

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