Liu G M, Hanigan M D, Lin X Y, Zhao K, Jiang F G, White R R, Wang Y, Hu Z Y, Wang Z H
Ruminant Nutrition and Physiology Laboratory, College of Animal Science and Technology, Shandong Agricultural University, Taian 271018, P. R. China.
Department of Dairy Science, Virginia Tech, Blacksburg 24061.
J Dairy Sci. 2017 May;100(5):4038-4050. doi: 10.3168/jds.2016-11973. Epub 2017 Feb 23.
Two studies were undertaken to assess the effects of individual essential AA supplementation of a protein-deficient diet on lactational performance in mice using litter growth rates as a response variable. The first study was designed to establish a dietary protein response curve, and the second to determine the effects of Leu, Ile, Met, and Thr supplementation of a protein-deficient diet on lactational performance. In both studies, dams were fed test diets from parturition through d 17 of lactation, when the studies ended. Mammary tissue was collected on d 17 from mice on the second experiment and analyzed for mammalian target of rapamycin (mTOR) pathway signaling. Supplementation with Ile, Leu, or Met independently increased litter weight gain by 11, 9, and 10%, respectively, as compared with the protein-deficient diet. These responses were supported by independent phosphorylation responses for mTOR and eIF4E binding protein 1 (4eBP1). Supplementation of Ile, Leu, and Met increased phosphorylation of mTOR by 55, 34, and 47%, respectively, as compared with the protein-deficient diet. Phosphorylation of 4eBP1 increased in response to Ile and Met supplementation by 60 and 40%, respectively. Supplementation of Ile and Met increased phosphorylation of Akt/protein kinase B (Akt) by 41 and 59%, respectively. This work demonstrated that milk production responds nonlinearly to protein supply, and milk production and the mTOR pathway responded independently to supplementation of individual AA. The former demonstrates that a linear breakpoint model is an inappropriate description of the responses, and the latter demonstrates that no single factor limits AA for lactation. Incorporation of a multiple-limiting AA concept and nonlinear responses into milk protein response models will help improve milk yield predictions and allow derivation of diets that will increase postabsorptive N efficiency and reduce N excretion by lactating animals.
进行了两项研究，以蛋白质缺乏饮食中补充单一必需氨基酸对小鼠泌乳性能的影响为评估对象，将窝仔生长率作为反应变量。第一项研究旨在建立饮食蛋白质反应曲线，第二项研究则是确定在蛋白质缺乏饮食中补充亮氨酸、异亮氨酸、蛋氨酸和苏氨酸对泌乳性能的影响。在两项研究中，母鼠从分娩至泌乳第17天（即研究结束时）均喂食试验日粮。在第二项实验中，于第17天采集小鼠的乳腺组织，并分析雷帕霉素靶蛋白（mTOR）信号通路。与蛋白质缺乏饮食相比，单独补充异亮氨酸、亮氨酸或蛋氨酸可使窝仔体重增加分别提高11%、9%和10%。这些反应得到了mTOR和真核翻译起始因子4E结合蛋白1（4EBP1）的独立磷酸化反应的支持。与蛋白质缺乏饮食相比，补充异亮氨酸、亮氨酸和蛋氨酸分别使mTOR的磷酸化增加55%、34%和47%。补充异亮氨酸和蛋氨酸分别使4EBP1的磷酸化增加60%和40%。补充异亮氨酸和蛋氨酸分别使Akt/蛋白激酶B（Akt）的磷酸化增加41%和59%。这项研究表明，产奶量对蛋白质供应呈非线性反应，产奶量和mTOR信号通路对单一氨基酸的补充呈独立反应。前者表明线性断点模型不适用于描述这些反应，后者表明没有单一因素限制泌乳期的氨基酸。将多限制氨基酸概念和非线性反应纳入乳蛋白反应模型将有助于提高产奶量预测，并有助于制定能提高吸收后氮效率并减少泌乳动物氮排泄的日粮。
