Condensed Tannin Concentration of Two Lespedeza Species and Its Effect on In Vitro Methane and Total Gas Production.

According to the US EPA, enteric fermentation by ruminants, primarily that of domestic beef and dairy cattle, is responsible for 21% of total anthropogenic methane (CH₄) emissions. Results from previous studies indicate that feeding forages containing condensed tannins (CT) to ruminants may reduce the amount of CH₄ produced during enteric fermentation. However, total gas production could also decrease, which may suggest that organic matter digestibility of forages containing CT is less. The objective of this work was to compare in vitro total gas and CH₄ production between two warm season perennial herbaceous legumes known to contain CT, and to determine which is better for suppressing CH₄ while minimizing a reduction in total gas production. For this study we compared Lespedeza stuevei Nutt. (tall lespedeza), a North American native species, and Lespedeza cuneata (Dum. Cours.) G. Don (sericea lespedeza), an introduced species listed as a noxious weed in Colorado and Kansas that has gained attention in recent years for its anthelmintic activity in small ruminants. Both forages were fermented with cattle rumen fluid under anaerobic conditions for 48 hours using an in vitro gas production technique. The total CT (TCT) concentration of tall lespedeza was 11.71 %, which was greater (P<0.05) than that of sericea lespedeza (8.29 %). The fermentation of sericea lespedeza produced 15.05 mg CH₄/g DM, which was greater (P<0.05) than that of tall lespedeza (4.86 mg CH₄/g DM). There was no difference (P=0.47) between in vitro total gas production of tall lespedeza (21.54 ml) and sericea lespedeza (19.73 ml), indicating that total gas production was not negatively impacted by the greater TCT concentration of tall lespedeza as compared to sericea lespedeza. Results indicate that tall lespedeza is a promising alternative to sericea lespedeza vis-à-vis suppression of CH₄ production while maintaining greater levels of total gas production in vitro.