The complete hydrolysis of complex structures, such as plant cell walls, requires the application of a range of multifunction enzymes in appropriate quantities. However while xylanase and cellulase activities in the rumen are adequate, such that additional (exogenous) enzymes are not required, their action is restricted due to the close association between cellulose and hemicellulose and other polysaccharides and to extensive substitution. In particular the arabinoifuranosyl residues in the hemicellulose chain form ferulic acid cross-links with lignin, so limiting biodegradability. Thus the so-called minor enzymic activities may be critical in making additional cell wall sites available for microbial attachment and subsequent digestion. To examine this effect the ability of ferulic acid esterase (FAE), which releases ferulic acid, to enhance fibrolytic activity by rumen microorganisms was evaluated in vitro.