An approach to screening potential pasture species for condensed tannin activity

Freeze dried samples of the leaves of six tropical leguminous shrubs were s tudied. Digestibilities of dry matter (IVDMD) and nitrogen (IVND) were dete rmined in vitro using rumen fluid from sheep in the presence and absence of polyethylene glycol 4000 (PEG). The difference due to PEG, the tannin effect, was more marked for IVND than for IVDMD and varied with species. The improvement for Acacia boliviana, C alliandra 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). The tannin effect was poorly correlated with previously published (Jackson et al., 1996) data on the butanol CT levels in these samples: extractable C T (r(2)=0.0007); protein bound (r(2)=0.485); fib;re bound (r(2)=0.566); and total CT (r(2)=0.1473). The bound CT and total CT were negatively related to the PEG effect. Vanillin CT was positively correlated with the PEG effec t (r(2)=0.578). Two species, A. boliviana and C. calothyrsus, behaved diffe rently to the others. Omitting these from the regressions improved the rela tionships with both butanol extractable CT and total butanol CT and with va nillin CT (r(2)greater than or equal to 0.9). For new pasture species, screening by using this modified in vitro digestio n technique would avoid the problems of using a known CT standard or of iso lating CT standards for each species. It would also provide some informatio n on digestibility. (C) 2000 Published by Elsevier Science B.V.