Stable isotopes provide evidence that condensed tannins from sericea lespedeza are degraded by ruminal microbes

The objective of Trial 1 was to determine the effects of condensed tannins (CT) from sericea lespedeza [SL; Lespedeza cuneata (Dum. Cours.) G. Don] on in vitro digestible organic matter (IVDOM), total gas production (GP), methane (CH(4)) emission, and ruminal fluid parameters after fermentation. Substrates used in four 48-h in vitro fermentations were 100% bermudagrass [(Cynodon dactylon (L.) Pers.] hay (0SL), 100% SL hay (100SL), and a mix of both hays (50SL). Linear reductions were observed for all parameters (P < 0.05) with the inclusion of SL, except for CH(4) in relation to GP, that presented a quadratic effect (P = 0.005). In Trial 2, SL plants were enriched with (13)C–CO(2) to obtain pure enriched CT to identify the destination of fermentation end products of CT degradation. The enrichment of CT through the SL was successful (P < 0.001), and carbon originated from CT was detected in the fermentation end products [microbial mass, clarified rumen fluid, and in the CH(4) produced (P < 0.001)]. Therefore, inclusion of SL was effective in reducing in vitro CH(4) production and compound-specific tracing of δ(13)C abundance provided better quantitative understanding of the mechanisms of partitioning CT during ruminal fermentation processes.