Effects of dry plant extracts on fermentation and methanogenesis in continuous culture of rumen microbes

Thirteen plant extracts, selected for their high flavonoid content, were screened on their action on fermentation and protozoa numbers in 1 l dual outflow fermenters supplied with a 50:50 orchard grass hay+barley diet. Using a 214−10 fractional factorial design, we tested each extract at the rate of 0.5 g per day. The corresponding organic matter inflow was equal to 3.4% of the basal hexoses fermentation rate. Lavandula officinalis enhanced acetate (C2), propionate (C3) and butyrate (C4) outflows (+9.2, +11.9 and +11.4%, respectively), while Solidago virgaurea acted mainly on C2 (+11.3%) and C3 (+15.8%). Achillea millefolium increased C2 relative outflow (+5.7%) to the detriment of C4 (−7.9%). Propolis increased C3 production by 10.3%. Branched chain volatile fatty acids productions were favoured by A. millefolium and lowered both by Arnica chamissonis and Fagopyrum esculentum. Gas production was increased by L. officinalis (CO2: +11.9%; CH4: +13.7%) and S. virgaurea (CO2: +7.8%; CH4: +7.7%), whereas it was lowered by Equisetum arvense (CO2: −10.6%; CH4: −14.2%). Methanogenesis also decreased with Salvia officinalis (−8.2%). Protozoa numbers were little affected by plant extracts. In conclusion, the extracts which could be selected for further evaluation were L. officinalis and S. virgaurea for promoting the extent of fermentation, and E. arvense and S. officinalis for their possible inhibitory action on methane production.