Abstract
The objective of this study was to investigate the effects of dietary threonine and arginine levels on stress response, animal welfare score, antioxidant capacity, and jejunal morphology of broiler chickens raised under multiple stress conditions. A total of 280 21-d-old Arbor Acres broiler chickens were randomly allotted to 4 treatments with 8 replicates. Birds were raised under normal conditions (22.6 ± 0.6°C and 15.2 birds/m(2)) and 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(2)). Birds in positive control (PC) were raised under normal conditions, while the other groups were exposed to multiple stress conditions. A basal diet was assigned to PC and negative control (NC). Two additional diets were formulated to contain 1.3-fold higher concentrations of digestible threonine (Thr) or arginine (Arg) than the basal diet. The experimental diets and water were provided ad libitum for 14 d. Animal welfare score including gait score, footpad dermatitis, hock burn, and feather cleanliness was analyzed according to Welfare Quality® assessment protocol for poultry. To analyze stress response, antioxidant capacity, and jejunal morphology, 1 bird per replicate was euthanized by CO(2) inhalation. All data were analyzed by ANOVA using the PROC MIXED procedure of SAS (SAS Institute Inc., NC, USA). The replicate was considered an experimental unit. Significance for statistical tests was considered at P < 0.05. Results indicated that heterophil to lymphocyte ratio was less (P < 0.05) in PC group than in other groups. Birds in PC, Thr, and Arg groups had less (P < 0.05) feather corticosterone concentrations than those in NC group. For the animal welfare score, gait score, footpad dermatitis, hock burn, and feather cleanliness were not affected by dietary treatments and multiple stress conditions. Reactive oxygen species (ROS) in the liver were less (P < 0.05) in PC and Arg groups than in NC group. Birds in PC, Thr, and Arg groups had less (P < 0.05) nitric oxide (NO) values in the jejunum than in NC group. Villus height was greater (P < 0.05) in PC group than in NC, Thr, and Arg groups. Birds in PC group had greater (P < 0.05) goblet cell counts than in NC and Arg groups. In conclusion, multiple stress conditions increase the stress response and damage the liver and jejunum of broiler chickens. Increasing concentrations of digestible Thr and Arg in diets reduce stress response, ROS, and NO levels of broiler chickens exposed to multiple stress conditions.