Utilisation of tropical dry season grass by ruminants is increased by feeding fallen leaf of siris (Albizia lebbeck)

Albizia lebbeck (siris) is a tropical, dry season, deciduous, multi-purpose tree. Field observations indicate that fallen leaf is eaten by livestock. In this study, fallen leaf was offered to cattle as a supplement to poor quality hay from native pasture. Voluntary intake of leaf comprised 15% of the total diet but caused a 52% increase (P<0.10) in intake of the native hay and a 67% increase (P<0.10) in digestible dry matter (DM) intake. During co-fermentation in vitro of fallen leaf of siris with angleton grass (Dichanthium aristatum), fibre digestion proceeded faster in mixtures than would be expected from results with component substrates. Most of this associative effect was not due to the contribution of N by siris leaf, but due to the cell wall matrix. The soluble extract from siris leaf obtained by sequential extraction with boiling ethanol and water, when added to grass caused an inhibition of grass digestion by a diverse rumen microbial inoculum, but stimulated digestion by Ruminococcus flavefaciens AR67 and microbial consortia originating from addax and kudu antelopes. Responses varied with microbial inoculum, the maximum increase in neutral detergent fibre (NDF) digestibility was 110 g/kg (P<0.05) 72 h after inoculation with addax consortia. Most of the activity was retained on ultrafiltration (<3000 MW cut off) or after dilute acid hydrolysis and was similar to that obtained with extracts of green pasture legumes and eucalyptus leaves. When the water soluble fraction of siris leaf was dosed into the rumen of sheep fed rhodes grass (Chloris gayana) fed ad libitum at a level corresponding to 20% leaf, there was a 20% increase (P<0.01) in voluntary grass intake, but in situ digestibility was not affected. A similar response was obtained with the soluble fraction from lucerne (Medicago sativa). Fallen leaf of siris has considerable feed value as a supplement to dry season grass. This may be due to both its N content and a low molecular weight constituent, as well as the differing morphology and chemistry of the lignocellulose substrates in siris leaf and grass.