L-citrulline (L-Cit), a non-protein amino acid, has been implicated in several physiological functions including anti-inflammatory, anti-oxidative, and hypothermic roles, however, there is a paucity of information with regards to its potential in poultry production. This study was designed to investigate the effects of dietary L-Cit supplementation on the production performance, nitric oxide production, and antioxidant status of laying hens during summer period. Hy-Line Brown laying hens (n = 288, 34 weeks old) were allotted to four treatment, 6 replicates of 12 chickens each. Dietary treatments of control (basal diets), 0.25%, 0.50% and 1.00% L-Cit supplementation were fed to chickens for eight (8) weeks. Production performance, free amino acid profiles, nitric oxide production, and antioxidant properties were measured. Blood samples were collected at the 4th and 8th weeks of the experiment. Air temperature monitoring indicated an average daily minimum and maximum temperatures of 25.02 °C and 31.01 °C respectively. Dietary supplementation with L-Cit did not influence (P > 0.05) the production performance, and rectal temperature of laying hens. Egg shape index was increased (P < 0.05) with increasing levels of L-Cit. Serum-free content of arginine, citrulline, ornithine, tryptophan, histidine, GABA, and cystathionine were elevated, but taurine declined with L-Cit diets. Plasma nitric oxide (NOx) concentration was highest at 1% L-Cit. Likewise, nitric oxide synthase (NOS) activity for total NOS (tNOS) and inducible NOS (iNOS) were upregulated with increasing L-Cit levels, although, tNOS was not affected at the 4th week. Anti-oxidant enzymes including catalase and superoxide dismutase (SOD) were increased with L-Cit supplementation, however, SOD activity was unchanged at 4th week, while total anti-oxidant capacity increased at the 8th week. L-Cit supplementation attenuated the extent of lipid peroxidation, and also inhibited glutathione peroxidase activity. Dietary L-Cit supplementation modulated systemic arginine metabolism, nitric oxide synthesis, antioxidant defense system, and increased the egg shape index of laying hens during the summer season. 1% L-Cit supplementation proved most effective in potentiating these effects and may be adopted for feed formulation strategies.

中文翻译：

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日粮补充 L-瓜氨酸可调节夏季蛋鸡的一氧化氮合成和抗氧化状态

L-瓜氨酸 (L-Cit) 是一种非蛋白质氨基酸，与多种生理功能有关，包括抗炎、抗氧化和低温作用，然而，关于其在家禽生产。本研究旨在调查日粮中添加 L-Cit 对夏季产蛋鸡生产性能、一氧化氮产生和抗氧化状态的影响。Hy-Line Brown 蛋鸡（n = 288，34 周龄）被分配到 4 个处理组，每组 12 只鸡重复 6 次。将对照（基础日粮）、0.25%、0.50% 和 1.00% L-Cit 补充剂的日粮处理喂给鸡八 (8) 周。测量了生产性能、游离氨基酸谱、一氧化氮产生和抗氧化特性。在实验的第 4 周和第 8 周采集血样。气温监测显示平均每日最低和最高温度分别为 25.02°C 和 31.01°C。日粮添加 L-Cit 不影响（P > 0.05）蛋鸡的生产性能和直肠温度。蛋形指数随着 L-Cit 水平的增加而增加（P < 0.05）。精氨酸、瓜氨酸、鸟氨酸、色氨酸、组氨酸、GABA 和胱硫醚的无血清含量升高，但牛磺酸在 L-Cit 饮食中下降。血浆一氧化氮 (NOx) 浓度在 1% L-Cit 时最高。同样，总 NOS (tNOS) 和诱导型 NOS (iNOS) 的一氧化氮合酶 (NOS) 活性随着 L-Cit 水平的增加而上调，尽管 tNOS 在第 4 周没有受到影响。包括过氧化氢酶和超氧化物歧化酶 (SOD) 在内的抗氧化酶随着 L-Cit 补充剂的增加而增加，然而，SOD 活性在第 4 周没有变化，而总抗氧化能力在第 8 周增加。L-Cit 补充剂减弱了脂质过氧化的程度，也抑制了谷胱甘肽过氧化物酶的活性。日粮补充 L-Cit 可调节全身精氨酸代谢、一氧化氮合成、抗氧化防御系统，并在夏季增加蛋鸡的蛋形指数。事实证明，1% L-Cit 补充剂在增强这些效果方面最有效，可用于饲料配方策略。L-Cit 补充剂减弱了脂质过氧化的程度，也抑制了谷胱甘肽过氧化物酶的活性。日粮补充 L-Cit 可调节全身精氨酸代谢、一氧化氮合成、抗氧化防御系统，并在夏季增加蛋鸡的蛋形指数。事实证明，1% L-Cit 补充剂在增强这些效果方面最有效，可用于饲料配方策略。L-Cit 补充剂减弱了脂质过氧化的程度，也抑制了谷胱甘肽过氧化物酶的活性。日粮补充 L-Cit 可调节全身精氨酸代谢、一氧化氮合成、抗氧化防御系统，并在夏季增加蛋鸡的蛋形指数。事实证明，1% L-Cit 补充剂在增强这些效果方面最有效，可用于饲料配方策略。