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

Thirteen plant extracts, selected for their high ̄avonoid content, were screened on their action on fermentation and protozoa numbers in 1 l dual out ̄ow fermenters supplied with a 50:50 orchard grass hay‡ barley diet. Using a 214ÿ10 fractional factorial design, we tested each extract at the rate of 0.5 g per day. The corresponding organic matter in ̄ow was equal to 3.4% of the basal hexoses fermentation rate. Lavandula of®cinalis enhanced acetate (C2), propionate (C3) and butyrate (C4) out ̄ows (‡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 out ̄ow (‡5.7%) to the detriment of C4 (ÿ7.9%). 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. of®cinalis (CO2: ‡11.9%; CH4: ‡13.7%) and S. virgaurea (CO2: ‡7.8%; CH4: ‡7.7%), whereas it was lowered by Equisetum arvense (CO2: ÿ10.6%; CH4: ÿ14.2%). Methanogenesis also decreased with Salvia of®cinalis (ÿ8.2%). Protozoa numbers were little affected by plant extracts. In conclusion, the extracts which could be selected for further evaluation were L. of®cinalis and S. virgaurea for promoting the extent of fermentation, and E. arvense and S. of®cinalis for their possible inhibitory action on methane production. # 2000 Elsevier Science B.V. All rights reserved.