Gan Liping, Fan Hao, Nie Wei, Guo Yuming
The State Key Laboratory of Animal Nutrition, College of Animal Science and Technology, China Agricultural University, Beijing, 100193 People's Republic of China.
J Anim Sci Biotechnol. 2018 Oct 1;9:71. doi: 10.1186/s40104-018-0284-7. eCollection 2018.
Laying hens over 75 weeks of age commonly show great declines in immunity and production performance. It is unclear whether these declines can be relieved by supplementing with ascorbic acid (AA) in feed. Two trials were conducted to investigate the synthesis and metabolism of AA in layers of different ages and the effects of dietary supplemental AA on the performance and the immune and antioxidant statuses of 78 weeks old hens.
In Exp. 1, equal numbers (24 hens) of 35 weeks old (Young) and 75 weeks old (Old) layers were fed the same diet without AA supplementation for 4 weeks. In Exp. 2, 360 healthy 78 weeks old laying hens were randomly assigned to 4 treatments (basal diet supplemented with 0, 0.25, 0.5, or 1 g AA/kg diet) in an 8-week feeding trial.
The old hens tended to have decreased L-gulonolactone oxidase (GLO) synthase activity in the kidney and liver than that of the young hens ( = 0.07 and = 0.05, respectively). Compared with the young hens, the old hens had lower hepatic antioxidant capacity allowing for the lower thioredoxin (), thioredoxin reductase () and cytochrome b5 reductase () gene expression ( < 0.05), whereas increased sodium-dependent vitamin C transporter () 1 expression levels in the ileum and kidney and enhanced splenic and hepatic AA concentrations ( < 0.05). Dietary supplementation with AA significantly decreased GLO enzyme activity but increased splenic AA concentration and anti-bovine serum albumin IgG levels ( < 0.05) and tended to increase CD4 T lymphocyte numbers ( = 0.06) in serum. Supplementation of 0.25 g AA/kg diet significantly increased hepatic total antioxidant capacity (T-AOC, < 0.05) relative to the control group.
Laying hens could synthesize AA in both the kidney and the liver, though the GLO enzyme activities were 100 times greater in kidneys than in livers. The old laying hens had greater absorption and reabsorption capacity and higher AA retention in some tissues that did the young hens. Dietary supplementation of AA can improve the health of old layers by enhancing immunity and antioxidant capacity.
75周龄以上的蛋鸡通常免疫力和生产性能大幅下降。尚不清楚在饲料中添加抗坏血酸（AA）是否能缓解这些下降。进行了两项试验，以研究不同年龄蛋鸡体内AA的合成与代谢，以及日粮添加AA对78周龄蛋鸡生产性能、免疫和抗氧化状态的影响。
在试验1中，将数量相等（各24只）的35周龄（年轻组）和75周龄（老龄组）蛋鸡饲喂相同的不添加AA的日粮4周。在试验2中，将360只健康的78周龄蛋鸡随机分为4组，进行为期8周的饲养试验，4组分别饲喂基础日粮，以及在基础日粮中添加0、0.25、0.5或1 g AA/kg日粮。
老龄蛋鸡肾脏和肝脏中的L-古洛糖酸内酯氧化酶（GLO）合成酶活性相比于年轻蛋鸡有下降趋势（分别为P = 0.07和P = 0.05）。与年轻蛋鸡相比，老龄蛋鸡肝脏抗氧化能力较低，硫氧还蛋白（Trx）、硫氧还蛋白还原酶（TrxR）和细胞色素b5还原酶（cytb5R）基因表达水平较低（P < 0.05），而回肠和肾脏中钠依赖性维生素C转运蛋白（SVCT）1表达水平升高，脾脏和肝脏中AA浓度升高（P < 0.05）。日粮添加AA显著降低了GLO酶活性，但提高了脾脏AA浓度和抗牛血清白蛋白IgG水平（P < 0.05），且血清中CD4 T淋巴细胞数量有增加趋势（P = 0.06）。相对于对照组，添加0.25 g AA/kg日粮显著提高了肝脏总抗氧化能力（T-AOC，P < 0.05）。
蛋鸡可在肾脏和肝脏中合成AA，尽管肾脏中GLO酶活性比肝脏中高100倍。老龄蛋鸡在某些组织中的吸收和重吸收能力以及AA潴留量比年轻蛋鸡更高。日粮添加AA可通过增强免疫力和抗氧化能力来改善老龄蛋鸡的健康状况。
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