In pursuit of the ideal dietary amino acid profile for dairy calves

氨基酸是蛋白质的基本成分。断奶前的犊牛，即以牛奶为食的犊牛，利用牛奶中的氨基酸合成身体蛋白质，如肌肉和消化道。今天的许多小牛都是用牛奶替代品而不是全脂牛奶喂养的。与全脂牛奶相比，牛奶替代品含有不同的氨基酸，因此，如果一种氨基酸供应不足，小牛的生长可能会受到限制。在这个研究项目中，我将研究用不同的氨基酸补充牛奶替代品的效果。我将测量对乳制品生产商具有重要经济意义的变量，如犊牛生长率、腹泻发生率和其他健康问题。我还将测量这些补充氨基酸是如何被小牛使用的，特别是它们是如何被消化道使用的。消化道依赖氨基酸作为蛋白质来源和能量来源。当氨基酸不与蛋白质结合时，它们会被降解，可以用作能量来源。在一些物种中，如猪，消化道优先使用氨基酸作为能量来源，而不是葡萄糖，葡萄糖是身体大多数组织的主要能量来源。在犊牛中，某些氨基酸作为能量来源的使用程度尚不清楚。这个研究项目的目标之一就是找出答案。如果我们以适当的数量和比例为小牛提供氨基酸，组织生长将得到最大限度的提高，小牛将高效利用氨基酸。通过补充特定的氨基酸，我们可能能够减少我们喂给小牛的蛋白质总量，这将转化为对小牛和乳制品生产商的积极影响——降低腹泻的发生率，更健康的小牛，更低的饲料成本和更快的增长速度。研究表明，在断奶前生长更快的小牛在第一次泌乳时产奶量更多（可达1300公斤）。这对加拿大的乳制品行业来说是一个巨大的经济收益。此外，从这项建议中获得的知识将被纳入预测犊牛氨基酸需求的方程式，并允许犊牛以最大效率使用饲粮。

Amino acids are the building blocks of protein. Pre-weaned dairy calves, calves that rely on a milk diet, use amino acids from the milk to synthesis body proteins such as muscle and the digestive tract. Many of today's calves are fed on milk replacers instead of whole milk. Milk replacers have a different profile of amino acids compared to whole milk and therefore, if one amino acid is in short supply, growth of the calf may be limited. In this research program, I am going to examine the effects of supplementing milk replacers with different amino acids. I will measure variables that are economically important to the dairy producer, such as calf growth rate and the incidence of diarrhea and other health issues. I am also going to measure how these supplemental amino acids are used by the calf, particularly how they are used by the digestive tract. The digestive tract relies on amino acids both as a protein source and an energy source. When amino acids are not incorporated into proteins, they are degraded and can be used as an energy source. In some species, such as the pig, the digestive tract preferentially uses amino acids as an energy source instead of glucose, which is the primary energy source for most tissues in the body. In calves it is not known to what extent certain amino acids are used as an energy source. One of the objectives of this research program is to find this out. If we supply amino acids to the calf in the right amounts and in the right proportions, tissue growth will be maximized and the calf will use the amino acids with high efficiency. By supplementing specific amino acids, we may be able to reduce the total amount of protein that we feed to calves, and this will translate into positive effects for the calf and the dairy producer - lower incidence of diarrhea, healthier calves, lower feed costs and faster rates of gain. It has been shown that calves that grow faster in the pre-weaning period produce more milk (up to 1300 kg) in their first lactation. This represents an enormous economic gain for the dairy industry across Canada. In addition, the knowledge gained from this proposal will be incorporated into equations that predict the amino acid requirements of the calf and allow for the use of diets that will be used with maximum efficiency by the calf.