Introduction

Never before has the economic success of feed manufacturers been so heavily dependent on optimal and accurate amino acid composition as today. The effects on growth and feed conversion of animals are so impressive that the annual amount of synthetic methionine and lysine supplemented in feeds worldwide now exceeds 400,000 tonnes each. This generates growing demand for amino acid analysis of feed raw materials to improve the amino acid matrix for linear feed programming, but also as a quality assurance tool for compound feeds and pre-mixtures.

In the first edition of this book A.P. Williams reported on the state of amino acid analysis by reviewing the literature up to 1992. In this second edition the focus shall be mainly on the developments of the last 10 years. There are numerous publications on amino acid analysis, but only a small proportion are concerned with test matrices that are relevant to animal nutrition, such as feedingstuffs, food products, plants, silages, by-products of plant and animal origin, animal blood plasma, intestinal and ruminal contents; these are the topics which will be discussed here.

One of the most important developments of recent years was undoubtedly the long overdue international standardization of amino acid analysis in feedingstuffs. Analytical scientists at national European supervisory authorities, who in the 1980s had adopted different methods of analysis for the determination of total amino acids as standards in their respective countries, eventually joined forces in an international collaborative effort to establish a common EU methodology. Recently, after extensive groundwork, official EU methods for the determination of total and free amino acids in animal feedingstuffs and corresponding methods for tryptophan were passed (Commission Directives 98/64/EC and 2000/45/EC). International collaboration was also the basis for the analytical method adopted by AOAC International for the determination of total amino acids with the exception of tryptophan (AOAC, 1994). The official methods of analysis of the AOAC enjoy worldwide recognition as an authorative collection of analytical methods far beyond the NAFTA region. The reference method adopted for feed analysis was the chromatographic separation of amino acids with a cation exchanger resin followed by nin-hydrin derivatization. Sample preparation is virtually identical for the various methods. The

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© CAB International 2003. Amino Acids in Animal Nutrition, 2nd edition (ed. J.P.F. D'Meiio)

EU standard procedure for the determination of tryptophan in feedingstuffs utilizes alkaline hydrolysis with barium hydroxide and HPLC analysis with specific fluorescence detection.

A second important innovation was the development of robust, internationally usable near-infrared spectroscopy (NIRS) calibrations for amino acids for the major feed raw materials, based on reliable wet chemical reference analysis. These allow the rapid, simple analysis of the amino acid composition of raw materials today and up-to-date feed optimization. This development will also be described in detail.

A review article by Kivi (2000) which focuses on chromatographic and detection methods deserves special mention because it is an excellent addition to this review.

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