Changes in Condensed Tannin Concentrations of Native Texas Legumes as a Result of Clipping Height.

Native warm season forage legumes can be used in both natural and cultivated forage systems to provide nutrients to ruminants.  Condensed tannins (CT) in these legumes can have both positive (rumen bypass protein and parasite control) and negative (decrease in palatability and digestibility) effects in ruminants.  Three herbaceous perennial Texas legumes were selected for this 3-year study: Tweedy’s tick-clover (Desmodium tweedy Britton), tall bush-clover (Lespedeza stuevei Nutt.), and panicled tick-clover (D. paniculatum (L.) DC.). Response to defoliation was evaluated by measuring CT concentrations when plants were clipped at 10-, 20-, and 40-cm height.  Total condensed tannin (TCT) concentrations were greater than 120 g kg^-1 for tall bush-clover and panicled tick-clover.  Extractable condensed tannin (ECT) was highest in tall bush-clover (98 g kg^-1), lowest in Tweedy’s tick-clover (4 g kg^-1), with panicled tick-clover at 65 g kg^-1.  Fiber-bound condensed tannin (FBCT) concentrations did not differ between the species.  Protein-bound condensed tannin (PBCT) concentrations were highest for panicled tick-clover (53 g kg^-1), lowest for Tweedy’s tick-clover (8 g kg^-1) with tall bush-clover being intermediate (22 g kg^-1).  When comparing clipping heights, PBCT and FBCT concentrations were the same for each height.  The ECT concentration was intermediate (57.0 g kg^-1) at the 20-cm cut and did not differ from the 10- or 40-cm cuts.  The ECT concentration at the10-cm cut (48.0 g kg^-1) was lower than the ECT concentration at 40-cm (62.2 g kg^-1).  The TCT concentration was intermediate (87.5 g kg^-1) at the 20-cm cut and did not differ from the 10- or 40-cm cuts.  The TCT concentration at the 40-cm (92.4 g kg^-1) cut was higher than the TCT concentration at 10-cm (77.2 g kg^-1).  These three native legumes show potential as sources of plant CT for ruminants.