Fiber in Animal Nutrition

Dietary Fiber and Analytics 10 inorganic matter is measured. Because of the substantial solubilization of structural polysaccharides and lignin, this variable fraction only measures an incomplete and variable fraction of the fibrous carbohydrate components. The fraction should characterize the indi- gestible part of the feed mainly composed by cellulose in part in combination with lignin. There is no stringent division achieved bet- ween indigestible fiber and highly digestible parts. So frequently parts of the indigestible lignin can be found in the N free extract fraction. Beside these uncertainties, nevertheless crude fiber was an essential part of the equa- tions to estimate the energy content in diets for cats and dogs (NRC, 2006; Kienzle et al., 1998). However, dog foods with a crude fiber content above eight percent dry matter and with a high percentage of fermentable non starch polysaccharides (NSP) in their crude fiber fraction are systematically un- derestimated (NRC, 2006). 1.2.2 Detergent fiber An important progress in the fiber analysis was the development of the system with detergent solutions (NDF) according to Goering and van Soest (1970), which was improved and expanded during the following years (van Soest et al., 1991, Mertens, 2002). In this approach, the fractions of the fiber that are insoluble either in neutral detergents or in acid detergent are measured, and the residue after treatment of the ADF fraction with sulfuric acid is considered to be acid detergent lignin. By difference, hemicellulose (NDF – ADF) and cellulose (ADF – ADL) are calculated. However, it has been reported that water extractable and pectinous poly- saccharides are soluble in neutral detergent and that starch and proteinmay contaminate the NDF residue. Therefore van Soest et al. (1991) suggested adding α -amylase and sodium sulfite to avoid this contamination with starch and protein respectively (Uden et al., 2005). A further development was introduced by Mertens (2002a) recommending that all feed be amylase treated, that sodium sulfite will be used and that NDF will be reported on ash free basis. Feed with higher fat content should be pre-extracted with a suitable solvent. Kehraus and Südekum (2015a, b) publis- hed a sophisticated overview upon critical points in the lab routine, apparatuses used and special feeds. Fiber supply has a prominent role in rumi- nant nutrition due to rumen function and rumen health especially in high yielding cows. Therefore the combination of the ana- lytical fiber content and the physical form has to be considered. The physical effective NDF was developed as a combination of physical (sieving) examination with the classical NDF procedure (Mertens, 2002b; Zebeli et al., 2012). Also in rabbit nutrition a sufficient fiber supply is essential to prevent digestive troubles. Gidenne (2003) published a recommendation for digestible fiber defined as the sum of hemicelluloses (NDF – ADF) and water insoluble pectin. Certainly the author mentioned that in theory the difference of total dietary fiber and NDF residues should be an estimate of pectins. However, when applied to animal complete feeds, this estimate varies greatly. Because of the highly variable structure of water insoluble pectins and water soluble non starch polysaccharides no satisfying method is presently available to determine these compounds routinely found in animal feeds. © ERLING Verlag