Evaluation of 30 novel plant secondary compounds for gas production, methane concentration, nutrient digestibility and volatile fatty acid concentrations using in vitro batch culture fermentation

Abstract The objective of the current study was to evaluate 30 previously uncharacterised pure plant secondary metabolites (PSM) for effects on in vitro gas production (GP) and methane concentration. Purified compounds ( n = 4) were incubated in buffered rumen fluid for 48 h at a rate of 25 mg per g substrate. Gas production was measured using ANKOM RF pressure analysers and gas composition was measured using gas chromatography. Dry matter and fibre digestibility and volatile fatty acid (VFA) concentrations were determined. Data were analysed using a linear mixed model with fixed effect of treatment, random effect of experimental run and blank as a covariate and Dunnett’s test to compare each treatment to a control. Sabenine, apigenin, galangin, isoliquiritigenin, quercetin, rutin, vitexin, abscisic acid and uridine reduced methane concentration, with a tendency for reduction by kaempferol. Sabenine, thymol, apigenin, quercetin, rutin, vitexin, abscisic acid and uridine reduced methane production, with the greatest reduction occurring for rutin (81.8 %), vitexin (81.7 %) and thymol (80.5 %). Eight compounds increased methane production compared to control, with stigmasterol having the greatest increase (173.0 %). Out of the compounds that reduced methane emissions, a reduction in fibre digestibility was observed for all except quercetin and thymol. Minimal effects of PSM on VFA profile were observed, with myrtenal increasing proportion of acetate, alpha-humulene, alpha-longipinene and beta-caryophyllene increasing proportion of propionate and thymol, apigenin, hyperoside and verbenone increasing proportion of butyrate. Results suggest that quercetin and thymol warrant further exploration as potential feed additives to reduce methane emissions.