Effect of phenolic acids and phenolics from plant cell walls on rumenlike fermentation in consecutive batch culture

Information on the interaction between mixed populations in the rumen and plant phenolics is required to fully elucidate the limitations of phenolic compounds on forage digestibility. The objective of this study was to examine the degradation of Italian ryegrass (Lolium multiflorum L.) hay incubated with mixed ruminal populations in consecutive batch culture (CBC) with or without phenolic acids or phenolic compounds extracted from plant cell walls. Each CBC consisted of a series of 10 cultures (3 replicates per culture) inoculated (10%, vol/vol) in sequence at 48-h intervals with microbial suspension from the previous set of cultures. All cultures were grown on a semidefined medium containing Italian ryegrass hay, and each CBC was initiated with an inoculum from the rumen. Rumenlike fermentation characteristics were maintained in control CBCs by repeated inoculum transfer. Treatment CBCs were transferred as described above, but cultures 5, 6, and 7 were incubated in the presence of trans-p-coumaric, cis-p-coumaric, or trans-ferulic acid or phenolics extracted from the cell walls of maize stem or barley straw. Mean apparent dry matter disappearance in control CBC cultures was 495 mg per g of hay, whereas the presence of phenolics reduced the initial dry matter disappearance by 6.3 to 25.6%. trans-p-Coumaric acid and, to a lesser extent, the phenolics from cell walls of maize stem were the most inhibitory compounds for dry matter disappearance and for the production of volatile fatty acids; trans-p-coumaric acid altered the molar ratio of acetate/propionate/butyrate. The CBC further showed variations in the ability of the rumen microbial population to adapt to phenolic compounds.