Condensed Tannins in Herbaceous Legumes1

Abstract

Thirteen herbaceous legumes were examined for the presence of condensed tannins (flavolans). Flavolans were not present in herbage from Astragalus cicer L., Melilotus officinalis L., Medicago sativa L., Trifolium pratense L., T. repens L., and Vicia cracca L. Flavolans were present in herbage from Coronilla varia L., Lotus corniculatus L., Lespedeza cuneata Don., Onobrychis viciaefolia Scop., T. arvense L., T. campestre Schreb., and T. dubium Sibth. The absence of tannins from A. cicer, which is reported to be a nonbloating legume, may be an exception to the generalization that tannins are responsible for the prevention of bloat in ruminants grazing nonbloating legume forage crops.Flavolans were extracted from the tannin‐bearing species with methanol‐water (1:1) and were partially characterized to determine whether differences in the composition of flavolans might explain variation in nutritive value of legume forages. Flavolans were characterized by: identification of free monomer flavanols; the number of flavolan bands on paper chromatograms; and identification of compounds produced by degradation of flavolans in acidic solution Flavolans of all species examined were proanthocyanidins, including both procyanidins and prodelphidins. A procyanidin was present in L. cuneata and C. varia, crops which are reported to have low nutritive values, but the same procyanidin was not present in O. viciaefolia and L. corniculatus, crops which have high nutritive values. This work demonstrates that herbaceous legumes vary in flavolan composition and suggests that such variation may be related to differences in nutritive value.