Rubanza et al., 2003. Asian-Aust. J. Anim. Sci., 16 (10): 1429-1437

Browse tree legume leaves from Acacia spp. (A. nilotica, A. tortilis, A. polyacantha), Dichrostachys sp., Flagea villosa, Piliostigma thonningii, Harrisonia sp. were evaluated for nutritive potential (chemical compositions and degradability characteristics) compared to Gliricidia sepium. Effect of tannins anti-nutritive activity on digestibility was also assessed by polyethylene glycol (PEG) tannin bioassay. Crude protein (CP), ash, neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL) differed (P<0.05) between legume foliages. Mean CP, ash, NDF, ADF and ADL for fodder species tested were 158, 92, 385, 145 and 100 g/kg DM, respectively. CP ranged from 115 (P. thonningii) to 205 g/kg DM (G. sepium). Acacia spp. had moderate CP values (g/kg DM) of 144 (A. nilotica), to high CP in A. tortilis (188) and A. polyacantha (194) comparable to G. sepium. The forages had relatively lower fibre compositions. A. nilotica had (P<0.05) lowest NDF, ADF and ADL (182, 68 and 44) compared to P. thonningii (619, 196 and 130) g/kg DM, respectively. Except G. sepium, all fodder species had detectable high phenolic and tannin contents greater than 5% DM, an upper beneficial level in animal feeding and nutrition. Mean total phenolics (TP), total tannins (TT) and condensed tannins (CT) (or proanthocyanidins) for fodder species tested were 139, 113 and 43 mg/g DM, respectively. F. villosa had (P<0.05) lowest TP and TT of 65 and 56 mg/g DM, respectively, compared to A. nilotica (237 and 236 mg/g DM, respectively). The CT varied (P<0.05) from 6 (F. villosa) to 74 mg/g DM (Dichrostachys sp.). In vitro organic matter (OM) degradability (OMD) differed (P<0.05) between fodder species. G. sepium had (P<0.05) high degradability potential compared to A. polyacantha that had (P<0.05) the lowest OMD values. Forage degradability ranked: G. sepium > A. nilotica > P. thonningi > F. villosa > Dichrostachys sp. > A. tortilis > A.polyacantha. Addition of PEG resulted to (P<0.05) improvement in in vitro OM digestibility (IVD). Increase in IVD was mainly due to binding action of PEG on tannins; and represents potential nutritive values previously depressed by tannins anti-nutritive activity. Browse fodder has potential as sources of ruminal nitrogen especially for ruminants consuming low quality roughages due to high protein, lower fibre compositions and high potential digestibility. However, utilization of browse supplements in ruminants is hampered by high phenolic and tannin contents. Deactivation of tannin anti-nutritive activity, possibly by feeding tanniniferous browse with other readily available nitrogen sources to dilute tannin anti-nutritive activity could improve utilization of browse fodder supplements. Further studies are needed to assess browse fodder palatability and intake, and their effect on growth performance in ruminants.