digestibility of the rations according to browse level are reported by Miranda (1989, Monographie n°7 ILCA) and Fall (1993, Thes Doct Univ ENSAM, France). The non-additivity of the ration components owing to the occurrence of digestive interactions, suggested application of regression method rather than difference method to evaluate the in vivo digestibility of tree forage based rations. To check the hypothesis of digestive interactions occurrence in the digestion of F. albida based rations, rumen cellulolytic capacity were measured in Zebu cattle fed with rations containing variable level of F. albida pods. Cellulolytic capacity of rations was evaluated by measuring rumen in sacco dry matter degradation (DMD) of a standard feed, peanut hay, in Gobra Zebu at the LNERV station of ISRA (Dakar, Senegal). Mature F. albida pods, collected in the Senegalese groundnut basin during the fresh dry season in 1994, were included in the ration of Gobra Zebu at a level varying from 0 to 75 % of the total ration. The basal diet was made of rice straw and peanut cake in the constant proportion of 85/15 (w/w). To avoid the influence of intake level in the digestion, cattle were fed on a restricted basis of 55 g/kg LW for all tested rations.
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