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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Research » Publications at this Location » Publication #142802

Title: CHALLENGES IN MEASURING INSOLUBLE DIETARY FIBER

Author
item Mertens, David

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/2/2003
Publication Date: 12/1/2003
Citation: Mertens, D.R. 2003. Challenges in measuring insoluble dietary fiber. Journal of Animal Science. 81:3233-3249.

Interpretive Summary: Dietary fiber is an important characteristic for describing feeds and indicating their nutritive value. Unlike humans who cannot digest it, ruminants such as cattle and sheep a stomach that allows them to digest fiber by microbial fermentation. Because ruminants can ferment it, their diets typically contain 30% or more of fiber, compared to less than 2% dietary fiber in our diets. However, even for them, dietary fiber is difficult to digest, and high fiber content in a feed indicates that it has lower nutritive value. Thus, measuring dietary fiber in feeds or diets is an important tool in evaluating their nutritional contribution to cattle and sheep. We have measured dietary fiber in animal feeds for over 150 years using a variety of analytical methods. However, methods for measuring dietary fiber do not have equal value in providing nutritional information. The challenge for the researcher, nutritionist, and analyst is to select methods that are relevant and reproducible. Without relevance there is no reason to measure dietary fiber and without reproducibility there is no value in doing so. For ruminants, insoluble dietary fiber is one of the most important characteristics of the diet. Relevance of dietary fiber methods is based on their ability to match the nutritional definition of insoluble dietary fiber. Reproducibility is determined by experiments in which analytical laboratories are each sent a sample of several feeds and the agreement among their results is determined. In this review, all current methods for insoluble dietary fiber that have tested for reproducibility were compared. It was concluded that amylase-treated neutral detergent fiber is the best routine method for measuring insoluble dietary fiber at present. More accurate and well-standardized unsoluble dietary fiber methods will ensure that feeds are evaluated correctly and that rations are formulated to better match animal requirements.

Technical Abstract: The objectives of this review are to define the criteria needed to evaluate insoluble dietary fiber (IDF) methods, discuss their relevance in meeting nutritional needs, describe problems with empirical IDF methods, and assess their relative merits. The challenge for the researcher, nutritionist, and analyst is to select methods that are relevant and reproducible. Without relevance there is no reason to measure IDF and without reproducibility there is no value in doing so. Ruminants and non-ruminant herbivores have gastrointestinal adaptations that use symbiotic microbial fermentation to promote the digestion of dietary fiber. For these animals, the appropriate physiological definition for selecting IDF methods may be the organic fraction of the diet that is indigestible or slowly digesting and occupies space in the gastrointestinal tract. Several current methods including amylase-treated neutral detergent fiber (aNDF) and the enzymatic-gravimetric methods for measuring total dietary fiber (TDF) appear to be relevant for measuring IDF. The aNDF method has been evaluated by collaborative studies and obtained of standard deviation of reproducibility of 1.3%. Insoluble dietary fiber methods, based on TDF have been evaluated using too few feed materials to make statistically valid conclusions, but the reproducibility of IDF, for the few feeds evaluated, were similar to the detergent fibers (0.94 to 2.40%). The sum of insoluble non-starch polysaccharides and lignin agrees with IDF measured by NDF, but the reproducibility of TDF using the acid hydrolysis is less than other dietary fiber methods. For routine nutritive evaluation of feeds and formulation of rations, aNDF seems to a reasonable choice for measuring IDF.