Effects of dry plant extracts on feed degradation and the production of rumen microbial biomass in a dual outflow fermenter

Using a 214–10 fractional factorial design, 13 plant extracts containing flavonoids were screened to determine their influence on rumen microbial metabolism in continuous culture systems. Each extract was supplied at the rate of 0.5 g per day, which corresponded to a concentration of 15 g kg−1 dietary dry matter (DM). Outflow of VFA was enhanced with Lavandula officinalis (+9.8%) and Solidago virga-aurea (+6.4%), but starch degradability was not modified, while NDF and ADF degradabilities increased with Achillea millefolium and decreased with Betula alba and Equisetum arvense. True degradability of crude protein (CP) increased with A. millefolium (+5.8%) and Dactylis glomerata (+6.1%), and decreased with Arnica chamissonis (−5.8%) and L. officinalis (−7.1%). Net production of microbial protein increased by 8.7% with A. millefolium. Efficiency of microbial protein synthesis was improved by A. millefolium (+10% from a basal value of 27.7 g N kg−1 FOM), and lowered by L. officinalis (−12.3%). Initiating a sequential experimental approach by a moderately sized 214–10 design allowed us to isolate L. officinalis, and S. virga-aurea on the basis of their stimulating effect on fermentation, and A. millefolium for increasing both degradabilities of CP and cell-wall constituents and efficiency and yield of biomass production. The information gained at this first step must now be reassessed with a full resolution design, which will protect against misinterpretations due to interactions among the three remaining plant extracts.