INTAKE, DIGESTION, AND NITROGEN-UTILIZATION BY SHEEP FED TROPICAL LEGUMES WITH CONTRASTING TANNIN CONCENTRATION AND ASTRINGENCY

We conducted an experiment to determine the effects of concentration a nd astringency of extractable and bound condensed tannins (CT) in trop ical legumes on intake, digestibility, and nitrogen (N) utilization by sheep. The test legumes (Desmodium ovalifolium and Flemingia macrophy lla) had similar concentrations of extractable CT (90 g/kg DM) but dif ferent concentrations of bound CT and astringency of tannins. Chopped, sun-dried forage of each legume was sprayed with either water (contro l) or polyethylene glycol (PEG, 35 g/kg of DM) to bind extractable CT and fed daily (26 g/kg BW) to eight sheep with ruminal and duodenal ca nnulas. The sheep also received starch-extracted cassava meal intrarum inally (4 g/kg BW) as a constant source of readily fermentable carbohy drates. Intake of the two legumes was not different (P > .05), but it increased an average of 10% (P < .01) when extractable CT were reduced from 90 to 50 g/kg of DM with PEG. Ruminal and total tract digestibil ities of OM, NDF, and ADF were greater (P < .01) with D. ovalifolium t han with F. macrophylla and increased for both legumes with the additi on of PEG. Greater (P < .01) N flow to the duodenum, N absorbed from t he intestine, and fecal N were observed with F. macrophylla than with D. ovalifolium. Extraction of CT with PEG resulted in less (P < .05) r uminal escape protein and less (P < .01) fecal N with both legumes, bu t apparent postruminal N digestion was not affected. Changes in the co ncentration of extractable CT in tropical legumes can significantly af fect forage intake, digestion, and N utilization by sheep.