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Gravimetric Determination of Amylase-Treated Neutral Detergent Fiber in Feeds with Refluxing in Beakers or Crucibles: Collaborative Study

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As an important constituent of animal feeds, fiber represents the portion of feeds that is bulky and difficult to digest. The neutral detergent fiber (NDF) method, developed over 30 years ago, is the method of choice for measuring total fiber in forages and other feeds. Several modifications that were made to improve its general applicability to all feeds and others developed in individual laboratories often resulted in variability among laboratories in measuring NDF. The amylase-treated NDF (aNDF) method, therefore, was developed as an accurate and precise method of measuring total insoluble fiber in feeds. A collaborative study was conducted to evaluate the repeatability and reproducibility of the aNDF method over the full range of animal feed materials. Twelve laboratories representing research, feed company, regulatory, and commercial feed testing laboratories analyzed 11 materials as blind duplicates. The materials represented feed matrixes, including animal products; high-protein, high-fat, and high-pectin feeds; oil seeds; grains; heated by-product feeds; and legume and grass hays and silages. Materials selected varied in chemical composition and contained 0–90% aNDF, 1–16% ash, 1–20% crude fat, 1–40% crude protein, and 0–50% starch. Correcting results for changes in blanks and reporting results as ash-free aNDF organic matter (aNDFom) improved the repeatability and reproducibility of results when aNDF was <25%. The within-laboratory repeatability standard deviation (sr) for percentage aNDFom in feeds varied from 0.21 to 1.82 and among-laboratory reproducibility standard deviation (sR) varied from 0.37 to 2.24. The HORRAT was <2 for all materials except feed materials containing >10% fat. However, standard deviations of repeatability and reproducibility for feeds with >10% fat were similar to those of other materials. It is recommended that the aNDF method be accepted for Official First Action status.
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Document Type: Research Article

Affiliations: U.S. Department of Agriculture, Agricultural Research Service, U.S. Dairy Forage Research Center, 1925 Linden Dr West, Madison, WI 53706-1108.

Publication date: 01 November 2002

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  • The Journal of AOAC INTERNATIONAL publishes refereed papers and reviews in the fields of chemical, biological and toxicological analytical chemistry for the purpose of showcasing the most precise, accurate and sensitive methods for analysis of foods, food additives, supplements and contaminants, cosmetics, drugs, toxins, hazardous substances, pesticides, feeds, fertilizers and the environment available at that point in time. The scope of the Journal includes unpublished original research describing new analytical methods, techniques and applications; improved approaches to sampling, both in the field and the laboratory; better methods of preparing samples for analysis; collaborative studies substantiating the performance of a given method; statistical techniques for evaluating data. The Journal will also publish other articles of general interest to its audience, e.g., technical communications; cautionary notes; comments on techniques, apparatus, and reagents.
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