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

加拿大典型奶牛将日粮氨基酸转化为乳蛋白的效率可能比现在高50%。为泌乳奶牛制定减少氮排泄到环境中的日粮，需要准确预测乳蛋白对营养摄入量变化的反应。基于对生长动物的新研究，我们假设乳蛋白的合成是由影响奶牛乳腺中翻译酶活性的信号蛋白调控的。我们的目标是：1)通过给奶牛施加氨基酸失衡和缺乏来测试上述信号假设，无论有无葡萄糖；2)量化不同氨基酸和葡萄糖供应条件下氨基酸向乳蛋白转移的部分效率；3)与可变部分效率相比，测试使用每种必需氨基酸转移到牛奶中的固定效率来预测牛奶蛋白质产量的准确性。为了实现目标1和目标2，我们将在泌乳奶牛身上进行一系列的皱胃灌注试验，首先确定哪些氨基酸对乳蛋白产量的影响最大，然后研究这些特定氨基酸的剂量和葡萄糖反应。预测牛奶中氨基酸捕获效率的方程式将被开发并纳入牛顿计算机模型，工业合作伙伴使用该模型为加拿大140万头奶牛中约30%的奶牛制定口粮。为了实现目标3，我们将进行一项奶牛饲养试验，在该试验中，我们将给奶牛喂食2种不同的日粮，并将观察到的牛奶和蛋白质产量与恒效率模型和变效率模型预测的产量进行比较。本项目拟聘用博士后2人、研究生1人、本科生2人。该研究结果将被工业合作伙伴用于更新奶牛饲料配方计划，并促进加拿大奶牛场蛋白质效率的提高。提高奶牛对日粮蛋白质的利用效率将提高奶牛企业的盈利能力，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.