Nitrogen partition in cell structures of tropical browse plants compared with temperate forages: influence on their in situ degradation pattern

The N ruminal degradation of tropical browse plants was compared with that of forages harvested in temperate regions, and the relationships between in situ N degradability and detergent fibre N content examined. Six browse plants were collected during the hot dry season in the semi-arid zone of West Africa (Senegal). Six hays were prepared from forages grown at Clermont-Ferrand, a semi-mountainous area in a temperate zone. We measured the partition of nitrogen (N) in feedstuffs with the detergent fibre system and the N and fibre N ruminal degradation with the nylon bag technique. Nitrogen in the neutral detergent fibre (expressed as percent total N) varied from 10 to 64% for browses and from 23 to 48% for hays. For browses, an important part of the cell wall N was located in the acid detergent fibre (ADFN). As a consequence of these chemical composition variations, there were large differences in N degradability of the browses, from 28% (leaves ofGuiera senegalensis) to 86% (pods ofAcacia raddiana). It was closely related to ADFN contents (RMSE = 3.6;R2 = 0.98). The extent of N degradability variations was much lower for hays, from 70 to 79%.