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Condensed tannins concentration of selected prairie legume forages as affected by phenological stages during two consecutive growth seasons in western Canada

Li, Y., Iwaasa, A. D., Wang, Y., Jin, L., Han, G. and Zhao, M. 2014. Condensed tannins concentration of selected prairie legume forages as affected by phenological stages during two consecutive growth seasons in western Canada. Can. J. Plant Sci. 94: 817-826. Studies have shown that condensed tannins (CT) at appropriate concentrations improve nutrient digestion in animals and influence ecosystem processes. However, knowledge of CT concentration in different phenological stages and different plant parts of non-conventional legumes growing in the western Canadian prairies is lacking for feed and grazing management. The research objectives were to determine the level and distribution of total CT (TCT), extractable CT (ECT) and protein-bound (PCT) or fiber-bound CT (FCT) concentrations in the whole plant of legume forages at different phenological (vegetative, flowering, seed maturity) stages and plant parts (leaves, stems, inflorescences and inflorescences+seedpods) using the Butanol-HCl procedure. Whole plant samples of purple prairie clover (Dalea purpurea Vent.), white prairie clover (D. candida Michx. ex Willd), sainfoin (Onobrychis viciifolia Scop.) and Canadian milkvetch (Astragalus canadensis L.) were collected in the 2011 and 2012 growing seasons from replicated small trial plots at vegetative, flowering and seed maturity stages. Species, phenological stages and their interactions all significantly affect the TCT, ECT, PCT and FCT concentrations in whole plant and plant parts (P<0.001). Concentrations of ECT and TCT increased for all species as they matured from vegetative to seed maturity, except for sainfoin where the vegetative stage had the highest ECT and TCT levels. The highest mean ECT and TCT concentrations for purple prairie clover and white prairie clover were found in the inflorescences part at flowering stage, while sainfoin had the highest ECT and TCT concentrations in the leaves at vegetative stage. There was little variation for PCT among different phenological stages in whole plant for species except for purple prairie clover and white prairie clover which had higher (P<0.05) PCT at seed maturity than at flowering stage. Only trace amounts of FCT were detected from either whole plant or different fractions of all plant species, except Canadian milkvetch. Condensed tannins were not observed in Canadian milkvetch except for trace amounts in the seed coat at seed maturity stage. The results demonstrate that legumes differ in their condensed tannin content which could potentially be used in pasture management.