Technical Note: Predicting ruminal methane inhibition by condensed tannins using nonlinear exponential decay regression analysis

Methane (CH4) is a potent greenhouse gas that is normally produced by microbial fermentation in the rumen and released to the environment mainly during eructation. Prediction of ruminal CH4 production is important for ruminant nutrition, especially for the determination of ME intake to assess the amount of total GE available for metabolism by an animal. Equations have been developed to predict ruminal CH4 production based on dietary constituents, but none have considered condensed tannins (CT), which are known to impact CH4 production by ruminants. The objective was to develop an equation to predict ruminal CH4, accounting for CT effects. Methane production data were acquired from 48-h in vitro fermentation of a diverse group of warm-season perennial forage legumes containing different concentrations of CT over the course of 3 yr (n = 113). The following nonlinear exponential decay regression equation was developed: CH4 = 113.6(-0.1751) x CT - 2.18 (r(2) = 0.53, P < 0.0001), in which CH4 is expressed in grams per kilogram of fermentable organic matter and CT is in percentage of the DM. This equation predicted that CH4 production could be reduced by approximately 50% when CT is 3.9% DM. This equation is likely more accurate when screening CT-containing forages for their potential ability to mitigate in vitro CH4 production by ruminants when the CT concentration is greater than 3% DM. Therefore, despite the degree of variability in ruminal CH4 production, this equation could be used as a tool for screening CT-containing forages for their potential to inhibit ruminal CH4. Future research should focus on the development of predictive equations when other potential reducers of ruminal CH4 are used in conjunction with CT.