Amino acid research infusion studies in dairy cows to improve estimates of protein efficiency

加拿大典型的奶牛将饲料中的氨基酸添加到牛奶蛋白质中的效率可能比现在高出50%。为哺乳奶牛制定日粮，以减少向环境中排泄的氮，需要准确预测牛奶蛋白质对营养摄入量变化的反应。基于对生长动物的新研究，我们假设牛奶蛋白质的合成是由信号蛋白调节的，这些信号蛋白影响奶牛乳腺中翻译酶的活性。我们的目标是1)通过给奶牛施加氨基酸失衡和缺乏来检验上述信号假说，无论有没有葡萄糖；2)量化不同氨基酸和葡萄糖供应条件下氨基酸转移到牛奶蛋白质的部分效率；以及3)测试使用固定的每种必需氨基酸转移到牛奶中的效率与可变的部分效率相比预测牛奶蛋白质产量的准确性。目标1和目标2将在哺乳期奶牛身上进行一系列皱胃输液实验，旨在首先确定哪些氨基酸对乳蛋白产量影响最大，然后研究这些特定氨基酸的剂量和葡萄糖反应。将开发预测牛奶中氨基酸捕获效率的方程，并将其纳入工业合作伙伴使用的牛顿计算机模型，以制定加拿大140万头奶牛中约30%的日粮。目标3将用2种不同的饲料喂养奶牛，并将观察到的产奶量和蛋白质产量与恒定和可变效率模型预测的产奶量进行比较。该项目将雇用两名博士后研究员、一名研究生和两名本科生。这些发现将被工业合作伙伴用来更新可操作的奶牛饲料配方计划，并促进加拿大奶牛场蛋白质效率的提高。奶牛对饲料蛋白质的更有效利用将提高乳制品企业的盈利能力，并减少农业向环境中释放的氮。

The efficiency with which the typical dairy cow in Canada incorporates dietary amino acids into milk protein could be 50% higher than it is today. Formulating diets for lactating cows so that less N is excreted into the environment requires an accurate prediction of the milk protein response to a change in nutrient intake. Based on new research in growing animals, we hypothesize that milk protein synthesis is regulated by signalling proteins that affect the activity of translational enzymes in the mammary glands of cows. Our objectives are 1) to test the above signalling hypotheses by administering amino acid imbalances and deficiencies to cows, with and without glucose; 2) to quantify the partial efficiencies of amino acid transfer to milk protein under conditions of varying amino acid and glucose supply; and 3) to test the accuracy of predicting milk protein yield using a fixed efficiency of transfer of each essential amino acid into milk compared to variable partial efficiencies. Objectives 1 and 2 will be met with a series of abomasal infusion experiments on lactating dairy cows designed to first identify which amino acids have the largest effect on milk protein yield, and then study those particular amino acids in terms of dose and glucose response. Equations to predict efficiency of amino acid capture in milk will be developed and incorporated into the Newton computer model used by the industrial partner to formulate rations for approximately 30% of the 1.4 million dairy cows in Canada. Objective 3 will be met with a cow feeding experiment where 2 different diets will be fed to cows and observed milk and protein yields will be compared with those predicted by constant and variable efficiency models. Two postdoctoral fellows, 1 graduate student, and 2 undergraduate students will be employed on the project. The findings will be used by the industrial partner to update an operational dairy feed formulation program and to facilitate improvements in protein efficiency on Canadian dairy farms. More efficient utilization of dietary protein by cows would lead to increased profitability of the dairy enterprise, and reductions in agricultural release of nitrogen into the environment.