Content of soluble and bound condensed tannins of three tropical herbaceous forage legumes

Abstract

The soluble, total-bound and fibre-bound condensed tannins (CT) in Cassia rotundifolia (cassia), Lablab purpureus (lablab) and Macroptilium atropurpureum (siratro) grown in tropical and sub-tropical regions were determined by the butanol–HCl method. Cassia had the highest total CT content of 29.5 g/kg DM than that of lablab, 16.9 g/kg DM which was intermediate while that of siratro, 12.4 g/kg DM, was the least. The legumes had most of their CT in the protein-bound fraction that constituted 54.5, 74.0 and 86.2% of the total CT in cassia, lablab and siratro, respectively. The fibre-bound CT content of the legumes was small and constituted 1.75, 3.71 and 1.41% of total CT in cassia, lablab and siratro, respectively. The low CT content of lablab and siratro may not be high enough to confer beneficial effects on legume nitrogen utilisation in ruminants as reported in other studies. However, the high CT content of cassia may cause astrigency leading to low intake. The presence of condensed tannins in these legumes may influence their utilisation as protein supplements to low quality roughages given to ruminants during the dry season in tropical regions.