Fiber in Animal Nutrition

53 Fiber sources routinely used in rabbit feed digested fibers are more simply estimated by the ADF criterion (figure 10). However, to these fiber fractions we should add other polysaccharides, belonging to the cell wall, but soluble in water, such as: soluble pectins, arabinoxylanes, beta-glucans, etc. The water solubility of polysaccharides is generally defined from solubility in hot water (80 °C). These water soluble fibers (SF) could be analysed through a complex procedure but without enough reproducibility for rou- tine laboratory analysis in animal feeding. Alternatively, SF could be evaluated by diffe- rences among two criteria “TDF-aNDFom”, since TDF procedure estimate the whole fiber content (soluble and insoluble), and also polysaccharides from the cell content (e.g. fructans, resistant starch, mannans). Using this procedure, soluble fiber ranges between 6 to 10% in rabbit feeds (Trocino et al., 2013). 4.3 Fiber sources routinely used in rabbit feed To formulate a complete feed, balanced in fibers and other nutrients, several rawmateri- als are used to reach the requirements for the rabbit (Chapter 4.6); their fiber composition is listed below (table 25). Quantitatively, the most important fiber supply is the poorly digested fiber fraction, namely the lignocellulose. Quantitatively, cellulose represents 40–50% DM in hulls of legumes and oilseeds, 10–30% DM in forages and beet pulps, 3–15 % DM in oilseeds or legume seeds. Other classical sources of cellulose are wheat straw, alfalfa and sunflower meal. Lignin concentration is under 5% for most concentrate feeds and young forages. The degree of lignification of the plant cell wall may reach 12% with ageing in forages, or up to 59% in grape seed meal. A high lignin concentration is found in ingredients, such as buckwheat hulls, grape pomace or rapeseed meal. Other specific raw materials, rich in lignins and cellulose are available for rabbit feeding, such products are extracted fromwood (Krieg et al., 2012), or a blend of ingredients “rich in fiber” ready to incorporate in a feed before pelleting. The second important supply in f iber corresponds to the digestible fiber fractions Ingredients Wheat straw Wheat bran Dehydrated alfalfa Sugar-beet pulp Sun- flower meal Soy- bean hulls Grape pomace aNDFom 80 45 46 47 38 62 64 ADFom 54 11 34 22 32 44 54 ADL 16 3 8 2 11 2 34 Crude fiber 40 10 27 19 26 36 26 WIP 2.2 2.9 7.6 27 8 10 8 TDF 85 46 48 68 42 68 72 SF (TDF-NDF) 5 1 2 21 4 6 8 Crude protein 3 15 16 9 31 11 13 WIP: water-insoluble pectins (uronic acids + neutral sugars of pectins insoluble in hot water) Table 25: Fiber fractions (% DM) in raw materials classically used in rabbit feeds, according to several methods of analysis © ERLING Verlag