An approach to screening potential pasture species for condensed tannin activity

Freeze dried samples of the leaves of six tropical leguminous shrubs were studied. Digestibilities of dry matter (IVDMD) and nitrogen (IVND) were determined in vitro using rumen fluid from sheep in the presence and absence of polyethylene glycol 4000 (PEG). fference due to PEG, the tannin effect, was more marked for IVND than for IVDMD and varied with species. The improvement for Acacia boliviana, Calliandra calothyrsus and Leucaena trichandra was large, intermediate with L. leucocephala and L. pallida and small with Gliricidia sepium (range 5.5–33.8 digestibility units). nnin effect was poorly correlated with previously published (Jackson et al., 1996) data on the butanol CT levels in these samples: extractable CT (r2=0.0007); protein bound (r2=0.485); fibre bound (r2=0.566); and total CT (r2=0.1473). The bound CT and total CT were negatively related to the PEG effect. Vanillin CT was positively correlated with the PEG effect (r2=0.578). Two species, A. boliviana and C. calothyrsus, behaved differently to the others. Omitting these from the regressions improved the relationships with both butanol extractable CT and total butanol CT and with vanillin CT (r2≥0.9). w pasture species, screening by using this modified in vitro digestion technique would avoid the problems of using a known CT standard or of isolating CT standards for each species. It would also provide some information on digestibility.