Fiber in Animal Nutrition

57 Inpact of fibers on digestion and performances such as the supply of lignocellulose (or crude fiber) is not sufficient enough to relate the fiber supply and the “level of security” of a feed for the growing rabbit. Thus apart from the quantity of ligno- cellulose, the quality of the ADF, i.e. the respective effects of lignins and cellulose have an impact on digestive health. Incre- asing the intake of lignins (criterion ADL = Acid Detergent Lignin) involves a rise of the feed conversion ratio, but reduces the risk of diarrhoea, as demonstrated in figure 13: a linear negative relationship (R²=0.77, n=6 study) between ADL and HRi. Moreover, an increase of the ratio lignins/cellulose (L/C) is associated with a lower HRi (Gidenne et al., 2001). There- fore it seems beneficial to incorporate in diets raw material having a high lignin and cellulose level, as reported in several trials for doe and growing rabbits (JRS, 2007). Globally, to reduce the risk of post-weaning digestive disorders, the lignin intake (ADL) for the growing rabbit, can be assumed to be 5 to 7 g/d, and that of cellulose from approximately 11 to 12 g/d. 4.4.5 Role of digestible fibers fractions “DF”. Hemicelluloses and water-insoluble pectins “WIP”, well valorise for rabbit growth, also modulate the digestive health. This new “combined” fiber criterion, called “digestible fibers (DF = HC + WIP) was studied, and the favourable effect of the DF on HRi, compared to starch intake, was demonstrated in several studies. However, from a set of 15 diets (5 studies) when ADF and the ratioDF/ ADF are varying within a study (figure 14), we observed a close relationship (R²=0.69) between the ratio DF/ADF and the HRi. This suggests that a too high incorporation of DF, with respect to lignins and cellulose, should be avoided to minimise the HRi during fattening. We thus recommend that the ratio DF/ADF remain under 1.3 for diets Figure 13: The risk of digestive trouble (HRi) in the growing rabbit is dependent of lignin “ADL” level y = 1.49X 2 - 19.8X + 85.4 R 2 = 0.77 Health Risk index, a er weaning % Gidenne et al., 2001 Bennegadi et al., 2001 Gidenne et al., 2000 Gidenne et al., 2004b Gidenne et al., 2004b Debray et al., 2002 Acid Detergent Lignin, % 70 60 50 40 30 20 10 0 0 2 3 1 4 5 7 6 8 © ERLING Verlag