SEASONAL VARIATION IN NUTRITIVE VALUE OF SOME BROWSE AND GRASS SPECIES IN BORANA RANGELAND, SOUTHERN ETHIOPIA

The Borana rangeland has diverse species of woody and herbaceous plants which are useful as forage. Chemical analysis, in vitro dry matter digestibility (IVDMD) and in sacco degradability study were conducted on feed samples collected from browse and grass species during the hot dry and main rainy seasons. Chemical analysis and IVDMD were done for Acacia brevispica, A. nilotica, A. seyal, A. tortilis, Balanites aegyptiaca, Grewia bicolor, G. tembensis, Rhus natalensis, Vernonia cinerascens and Maracaa and grass species Cenchrus ciliaris, Chrysopogon aucheri and P. mezianum while in sacco degradability was done for A. nilotica, B. aegyptiaca, G. bicolor, R. natalensis and C. aucheri. The crude protein content (CP) of the browse species was higher in the rainy season except A. seyal which had higher value in the dry season (210 g/kg DM). The condensed tannin (CT) concentration ranged from 1.2 to 332 g/kg DM in B. aegyptiaca and A. tortilis, respectively. The NDF and ADF were highest in G. tembensis and G. bicolor while lowest values were in A. nilotica and A. seyal in the dry season, respectively. During the rainy season G. tembensis had highest NDF (750.9 g/kg DM) and lowest was in A. nilotica (128.1 g/ kg DM). The IVDMD among the browse varied from 965.7 to 718.9 and 974.7 to 676.3 in the dry and rainy seasons, respectively. In grass species CP was from 56 to 78. The NDF ranged from 728 to 749 g/kg DM and from 673 to 709 g/kg DM in dry and rainy seasons, respectively. The IVDMD was higher in the rainy season (698.2-811.5 vs 577.8-620.2). The in sacco DM degradability was highest for A. nilotica followed by B. aegyptiaca and lowest was in C. aucheri. The browse had high feed potential based on chemical and digestibility/degradability values recorded in this study while grasses could be considered as moderate. Among the grasses, C. ciliaris and C. aucheri are promising in terms of the digestibility values. However this conclusion needs to be supported by animal experiments and knowledge of the local community.