NONSTARCH POLYSACCHARIDE COMPOSITION AND IN-VITRO FERMENTABILITY OF TROPICAL FORAGE LEGUMES VARYING IN PHENOLIC CONTENT

The fermentation kinetics of leaves of eleven tropical forage legumes varying in phenolic and condensed tannin content were investigated. The leaf samples were from Acacia cyanophylla, Chamaecytisus palmensis, Calliandra sp., Dioclea guianensis, Flemingia macrophylla, Leucaena leucocephala, Sesbania sesban, S. goetzei and three accessions of Tadehagi sp. (accession numbers 13269, 13275 and 23227). The phenolic, condensed tannin (bound condensed tannin and extractable condensed tannin) and non-starch polysaccharide (NSP = to dietary fibre) contents of leaves were determined. Leaves were incubated at 39 degrees C with rumen micro-organisms in a habitat-simulating medium and the fermentation kinetics investigated using a pressure transducer. The NSP content of leaves both pre-and post-incubation was quantified and proportional losses of the NSP constituents calculated. The NSP content of leaves ranged from 124-252 mg g(-1) dry matter, the major components in each case being cellulose-derived glucose and the uronic acids. In all samples, the most degradable NSP constituent was the uronic acids, closely followed by arabinose; cellulose-derived glucose and xylose were the least degradable NSP components. Samples ranked in terms of asymptotic gas-pool in descending order as follows: L. leucocephala = C. palmensis > D. guianensis > S. sesban > A. cyanophylla > S. goetzei > Tadehagi sp., (23227) > Tadehagi sp., (13269) > F. macrophylla > Calliandra sp. > Tadehagi sp., (13275). There were significant relationships between gas accumulation throughout the incubation and the NSP loss (NSPL) values at the end of the incubation. Moreover, the gas pool at the end of the incubation period and NSPL were significantly correlated (r = 0.90) with a yield constant (ml gas g(-1) NSP loss) of 200 ml. Furthermore, there were significant (P less than or equal to 0.05) negative relationships between both gas accumulation and NSPL and the phenolic and condensed tannin content of leaves.