妊娠后期母猪日粮中添加谷氨酰胺促胎猪生长的机理研究

Birth weight is positively related to neonatal survival, weanling body weight and the time to marketing. Sixty percent of fetal growth occurs during the last 30 days (d 85 to delivery) of gestation and the undersupply of nutrients from sow to fetal pig is the main cause for low birth weight. Based on physiological analysis, we found that uterine and umbilical uptake of Gln was the greatest among all amino acids in pregnant gilts and abundance of Gln in umibical vein or amiontic fluid of large fetus was higher than those in small fetus, implicating an important role for Gln in fetal growth and development. In support of this view,we found that supplementing 1% Gln to the diet of gilts during the last 30 days of gestation increased average birth weight and litter birth weight of live-born piglets while reducing the number of IUGR piglets,variation in birth weight, and preweaning mortality of live-born piglets by 39%, 33% and 46%, respectively, when compared with the isonitrogenous control. In this project, we would like to extend our research and to use metabolomic, proteomic and traditional biochemical techniques to investigate the machanism behind the growth-promoting effect of Gln by comparing the metabolites between maternal blood, umibilical vein and amiontic fluid of Gln-supplemented and those of the isonitrogenous control group, the capacity of placenta for nutrient transport, as well as the changes of amino acid profile, proteome and enzymes related to protein turnover in fetal tissues such as placenta, small intestine, live and muscle, with a goal to imporve the nutritional strategy for sow feeding.

仔猪出生重与其断奶成活率、断奶和同期出栏体重呈密切正相关。生产中母猪限饲策略导致的对胎猪营养供给不足是仔猪出生重低的最直接原因。60%的胎儿生长发生在妊娠期的后30天，基于生理学分析发现的妊娠后期母猪子宫摄取的谷氨酰胺（Gln）增加而羊水中Gln含量降低，以及大胎猪较小胎猪对应的脐带血和羊水中Gln含量较高的规律，通过在妊娠期后30天的母猪日粮中添加1%的Gln可增加仔猪的出生重、减少窝内体重变异及断奶前死亡率。本研究拟在此基础上，通过比较妊娠后期母猪日粮中添加Gln与否对110日龄母猪血、胎猪脐带血和羊水中氨基酸、脂肪酸、葡萄糖等生化指标与代谢组的影响，对胎盘蛋白质组和重要营养素转运能力的影响，以及对胎猪小肠、肝脏和骨骼肌蛋白质组、营养素代谢和蛋白质合成与降解的影响，从母体变化、母胎营养传递与胎猪生长的角度探讨Gln促胎猪生长与代谢程序化的作用机制，为进一步优化母体营养方案提供理论依据。

仔猪出生重与其断奶成活率、断奶和同期出栏体重呈密切正相关。生产中母猪限饲策略导致的对胎猪营养供给不足是仔猪出生重低的最直接原因。60%的胎儿生长发生在妊娠期的后30天，基于生理学分析发现的妊娠后期母猪子宫摄取的谷氨酰胺(Gln)增加而羊水中Gln含量降低，以及大胎猪较小胎猪对应的脐带血和羊水中Gln含量较高的规律，本研究通过在妊娠期后30天的母猪日粮中添加1%的Gln可增加仔猪的出生重、减少窝内体重变异、减少宫内生长受限（IUGR）仔猪数。同时，利用高效液相色谱和生化分析技术分析了母猪不同妊娠期和新生仔猪血浆游离氨基酸谱和血液生化指标，探讨母体对Gln添加的自身营养状况响应及母胎营养物质转运变化规律。仔猪屠宰分析发现妊娠后期母体添加Gln提高了仔猪肠道重量，增加了仔猪空肠绒毛高度和宽度、绒毛高度与隐窝深度比、黏膜厚度以及绒毛表面积。同时提高仔猪空肠组织中mTOR信号通路下游蛋白S6K和4EBP1的磷酸化水平；提高胞外基质和紧密连接蛋白的表达量。此外，本项目还以猪的肠道上皮细胞系IPEC为体外模型，探讨添加不同浓度的Gln对仔猪肠道细胞增殖及相关基因和蛋白表达情况的影响。结果发现：Gln缺乏会抑制肠细胞增殖，降低细胞中mTOR信号通路中mTOR和S6K蛋白磷酸化水平，促进细胞自噬水平发生；而添加Gln则可促进肠道上皮细胞增殖、提高单层细胞整合性，抑制在IUGR仔猪肠道中高表达的microRNA-29a的表达，同时提高了细胞中胞外基质和紧密连接蛋白等相关的基因和蛋白表达水平，为阐明Gln在猪肠道中的保护作用及生产中添加Gln改善肠道功能发育提供一定理论依据。本项目揭示了在妊娠后期母猪日粮中添加Gln对母体营养状况及氨基酸自母体向胎猪转运供给的影响，促进了胎猪生长以及仔猪组织尤其是肠道组织发育，为进一步优化母体营养方案提供了新的理论依据。