Improving Nitrogen Utilization in Dairy Cows

奶牛养殖既要有利可图，又要对环境问题敏感。蛋白质是奶牛口粮中最昂贵的成分，供应过剩会造成地面、水和空气污染。因此，如果饲料能够更好地平衡以提供所需的单个氨基酸（AA：蛋白质的组成部分），则可以通过降低饲粮蛋白质的投入来降低成本和污染。在这个整体框架内，我们目前正在研究AA如何与高能量营养素相互作用，重点是葡萄糖，以便描述减少蛋白质供应所需的能量条件，而不会对牛奶产量产生任何有害影响。事实上，当奶牛摄入蛋白质而不是葡萄糖时，通常会产生更多的牛奶和乳糖（其中含有葡萄糖）。为什么会发生这种情况，以及是否有其他更便宜或对环境影响更小的营养素可以替代这种作用，这些都需要研究。目前的研究计划建议使用最先进的方法，使用多导管的奶牛和用稳定同位素标记的葡萄糖（在体内自然存在）来跟踪各种组织如何利用营养来响应改变的蛋白质和/或能量供应。我们的研究计划旨在发展肠道、肝脏和乳腺对营养物质利用的基础知识，这些组织是利用AA和能量的主要组织。这一独特的知识将被整合到乳制品营养学家和加拿大农民使用的现有计划中，以平衡乳制品口粮，从而以最佳效率最大化产量。除了补充我们在AA和葡萄糖代谢方面的知识外，这些结果可以迅速转移到乳制品行业，并对农场实践产生直接影响，对加拿大的环境和农场经济都有好处。

Dairy farming has to be profitable and yet sensitive to environmental concerns. Protein is the most expensive component of dairy rations and excess supply contributes to ground, water and air pollution. Therefore, decreasing both costs and pollution can be achieved through a lower input of dietary protein if feeds were better balanced to provide the required individual amino acids (AA: the building blocks of proteins). Within this overall framework, we are currently studying how AA interact with energetic nutrients, with a focus on glucose, in order to delineate the energy conditions needed to reduce protein supply without any detrimental effect on milk production. Indeed often cows make more milk and milk lactose (which contains glucose) when supplied with protein rather than glucose. Why this happens and whether other nutrients, cheaper or with less impact on environment, can substitute for this role needs to be investigated. The current research program proposes to use state-of-the-art methodology using multi-catheterized cows and glucose labeled with stable isotopes (occurring naturally in the body) to follow how the various tissues use nutrients in response to altered protein and/or energy supply. Our research program aims to develop fundamental knowledge on utilization of nutrients by the gut, the liver and the mammary gland, the major tissues using AA and energy. This unique knowledge will then be integrated into existing programs used by dairy nutritionists and Canadians farmers to balance dairy rations in order to maximize outputs at optimal efficiency. In addition to complementing our knowledge on AA and glucose metabolism, these results can be rapidly transferred to the dairy industry and have an immediate impact on farm practice, with benefits to both the environment and farm economics in Canada.