Department of Animal Sciences, Purdue University, West Lafayette, IN 47907-2054, USA.
Poult Sci. 2011 Aug;90(8):1737-48. doi: 10.3382/ps.2010-01245.
Accurate estimation of ileal endogenous amino acid (EAA) losses is important when formulating diets on a standardized ileal digestible amino acid basis. In addition to the undigested and unabsorbed amino acids of dietary origin, amino acids of endogenous origin, which can be basal or diet specific, are found in digesta. The improvement in the techniques used in amino acid analysis as well as a shift from sampling excreta to ileal digesta has resulted in more accurate amino acid digestibility coefficients. Despite this, however, it is important to determine the amino acids in the digesta that are of endogenous origin. Although the need for standardization and its associated advantages is still subject to debate, it is important to evaluate how values from various methodologies compare. Several methods have been used to estimate ileal EAA flow. The classical methods, including the regression method, the use of nitrogen-free diet (NFD), and the fasted cecectomized rooster method, are the most widely used. The criticisms with the last 2 methods are that birds are not in a normal physiological state and the ileal EAA flow is, therefore, underestimated. Different methods have resulted in different endogenous flow estimates, with the NFD method having the lowest values when compared with flows from the regression and highly digestible protein methods. In addition to the influence of methods on ileal EAA flows, the influence of the age of the birds on flow is important. Data on EAA losses are copious in the literature; however, variation in data across and within laboratories calls for investigation of factors contributing to the variation. This review compares results from different methods and examines the issue of repeatability and consistency of EAA losses data from different laboratories. Finally, composition of an NFD for estimating EAA losses is proposed.
准确估计回肠内源性氨基酸 (EAA) 的损失在基于标准化回肠可消化氨基酸基础上配制日粮时非常重要。除了日粮来源的未消化和未吸收的氨基酸外，消化物中还存在内源性氨基酸，这些氨基酸可以是基础的或特定于日粮的。随着氨基酸分析技术的改进以及从排泄物采样到回肠消化物采样的转变，氨基酸消化率系数变得更加准确。然而，尽管如此，确定消化物中内源性氨基酸仍然很重要。尽管标准化的必要性及其相关优势仍存在争议，但评估各种方法的数值如何比较仍然很重要。已经使用了几种方法来估计回肠 EAA 流量。经典方法，包括回归法、使用无氮日粮 (NFD) 和禁食盲肠公鸡法，是最广泛使用的方法。后两种方法的批评是鸟类处于正常生理状态，因此回肠 EAA 流量被低估。不同的方法导致不同的内源性流量估计，与回归和高消化率蛋白方法相比，NFD 方法的流量最低。除了方法对回肠 EAA 流量的影响外，鸟类年龄对流量的影响也很重要。关于 EAA 损失的数据在文献中很多；然而，不同实验室之间和内部的数据差异要求调查导致这种差异的因素。本综述比较了不同方法的结果，并研究了不同实验室 EAA 损失数据的可重复性和一致性问题。最后，提出了用于估计 EAA 损失的 NFD 的组成。
