Increasing arginine supplementation alleviated heat stress and citrulline can effectively substitute arginine in broilers

This study was conducted to determine the optimal standard ileal digestible (SID) arginine (Arg) to SID lysine (Lys) ratio in broilers under cyclic heat stress. Additionally this study tested whether citrulline (Cit) can replace Arg under cyclic heat stress, based on the report that a large amount of Arg is metabolized in the liver while Cit can by-pass metabolism in the liver. A total of 360, one-day-old Arbor Acres broiler chickens with initial body weight of 34.50 ± 0.87 g were placed in 24 pens. The 24 pens were randomly assigned to four dietary treatments with six replicates of fifteen broiler chickens. Treatments were as follows: 1) NC (SID Arg : Lys =0.95), 2) PC (SID Arg : Lys=1.05), 3) Arg1.15 (SID Arg : Lys =1.15), 4) Arg1.25 (SID Arg : Lys =1.25), 5) Cit33 (supplementation of Cit at 33% of Arg supplementation in Arg1.15, 6)  Cit50 (supplementation of Cit at 50% of Arg in Arg1.15).  The Arg1.25 group had the highest BW on 32 days and BWG during the overall period (<italic>p</italic>&lt;0.05) than the NC groups. However, there was no significant difference (<italic>p</italic>&gt;0.05) on day 32 BW and BWG during the overall period in Arg supplemented groups (Arg1.15 and Arg1.25) and Arg replacement with Cit groups (Cit33 and Cit50). Arg1.25 and Cit33 groups had higher villus height (VH) in the duodenum, jejunum and ileum than the NC groups. Moreover, the Arg1.25 group had the lowest crypt depth (CD) in the jejunum and ileum than the NC group, while there was no significant difference (<italic>p</italic>&gt;0.05) between Arg supplementation and Arg replacement with Cit groups. Arg1.25 group had the highest arginase activity in the liver and total nitric oxide synthase (NOS) and arginase activity in the kidney than other treatments, but no statistical difference was observed (<italic>p</italic>&gt;0.05) in arginase in the liver among treatments. Collectively the results ascertain that Cit can effectively replace a certain part of dietary arginine in broiler diets.