Challenges in Quantifying Condensed Tannins and Their Impact On the Ruminal Degradability of Protein in Birdsfoot Trefoil.

There is considerable interest in defining optimal concentrations of condensed tannins (CT) for limiting wasteful pregastric proteolysis of protein in forage legumes. The butanol-HCl assay is widely used for quantifying extractable CT in forages, but the assay underestimates total CT when applied directly to plant material.  We found an optimized acetone-butanol-HCl assay with iron gave consistent linear responses with CT standards and increased estimates of total CT in birdsfoot trefoil by 2-fold over the standard method run without acetone. Our results also indicate the purity of CT standards must be determined to accurately estimate CT concentrations in plant tissues. Increases in CT linearly decreased the ruminal degradabilty of protein, but degree of protein protection from proteolysis was greatly influenced by the type of kinetic model used to fit in situ data. Thus results from in situ studeis must be validated by in vivo trials in order to define optimal CT concentrations for forage legumes such as birdsfoot trefoil.