Occurrence of digestive interactions in tree forage-based diets for sheep

The effect of browse level in the diet on the in vivo dry matter digestibility (DMD) in sheep and the DM degradation of peanut hay in the rumen of cattle-fed tree forage-based diets were investigated in order to detect the occurrence of digestive interactions between diet components. Selected browse species Acacia albida pods, Pithecellobium dulce, Adansonia digitata and Calotropis procera leaf samples were collected in the central regions of Senegal, sundried and stored in LNERV animal barns for in vivo trials. Classical in vivo balance trials were performed for each tree forage sample. The proportion of browse in the applied diet varied between 0 and 75% of DM. Regression and difference procedures were both tested to estimate the DMD of the browse component of the diet. DMD capacity in the rumen of three young Gobra bulls fed the browse-based diets was estimated by measurement of the in sacco dry matter degradation profile of a standard sample, peanut hay. For each sample, large variations were observed when the browse DMD was calculated by difference. Both total ration DMD and rumen DM degradation capacity were significantly (p<0.001) influenced by browse level in the diet. However, non-linear response of total diet DMD to increasing levels of browse was observed only in A. digitata and P. dulce indicating occurrence of digestive interactions in those species. Rumen DM degradation capacity varied according to plant species which played a major role in the observed digestion profile. Results suggest that the digestion of tree forages-based diets may be influenced by digestive interactions but the large variations observed in plant species show their importance. Optimal DM degradation occurred at 15–30% of browse level in the diet for both A. albida and A. digitata while for P. dulce it was at 50%. Corresponding browse digestibility was of 50%, 47.1%, 51.3% and 60.7% DM for A. albida, A. digitata, P. dulce and C. procera respectively. Further work using the regression method in a wider range of browse species could help confirm between-species variations.