Fiber in Animal Nutrition

Fiber in Rabbit Nutrition 52 tionship between specific fiber fractions and the digestive health of the growing rabbit has been analysed through a meta-analysis of a compilation of trials that do not use antibiotics (Gidenne, 2015a), since the EC policy strongly recommend to reduce the use of antibiotics in animal breeding (Chap- ter 4.5). Finally, we will propose new fiber requirements for the growing rabbit health based on several criteria and the Van-Soest procedure (Chapter 4.6). 4.2 Dietary fiber: definition and analy- tical criteria useful for rabbit feeds The concept of dietary fibers is larger than the cell wall botanical definition, since in animal nutrition it includes not only the cell-wall po- lysaccharides (cellulose, hemicelluloses, pectic substances, etc.), but also other components that are only fermented by the microbiota, such as: oligosaccharides, gums, resistant starch, inulin, etc. According to their botani- cal origin, theymay be associated with lignins and other non-carbohydrate components (e.g., polyphenols, waxes, saponins, cutin, phytates, resistant protein). Shortly, dietary fibers could be defined as the sum of lignins and fermentable polysaccharides of the plant cell wall. The main fiber fractions present in rabbit feeds could be classed respective to their digestion in the rabbit gut (Chapter 4.4): 1- lignins and cellulose, that are slowly fermented and thus poorly digested in the rabbit caecum (although lignin is theoretically indigestible); 2- hemicelluloses and pectins that are more quickly fermented and thus well digested in the rabbit caecum. With the sequential Van-Soest procedure we can estimate in animal feeds or rawmaterials, the lignins (ADL), the cellulose (ADFom- ADL) and the hemicelluloses (aNDFom- ADFom). However, pectins are not estimated with this procedure.Themajor part of pectins in rabbit feeds is insoluble in water, and they cannot be measured easily in feeds.Thus they are estimated in raw material from specific tables, such as those by the EGRAN group (Maertens et al., 2002). Consequently, to estimate the digestible fibers (DF) in a rabbit diet, we must add the hemicelluloses (HC, analysed) and water insoluble pectins (WIP, calculated from tables). Whereas the poorly Figure 10: Main fiber fractions, analytical criteria and relative digestion by the rabbit CF: Crude Fiber ; aNDFom: Neutral Detergent Fiber, assayed with a heat stable amylase and expressed free of ash; ADFom: Acid Detergent Fiber expressed free of ash; ADL: Acid Detergent Lignin Beta-glucans Galactomannans Pectic substances glucomannans, galactans, ... Hemicelluloses arabinoxylanes, xyloglucanes, ... Cellulose Lignins CF ADFom aNDFom Moderately digestible bers Poorly digestible bers ADL Cell walls © ERLING Verlag