The Dacron bag technique has been widely used to estimate degradation in the rumen. The drawbacks, such as variation in rinsing losses and inability to correct for microbial contamination, are well known. However, these effects also suggest the potential to use the technique in studies of microbial colonisation. Other studies in our laboratory have investigated the use of odd-chain fatty acids (C15:0 and C17:0) as markers of rumen microbial activity (Fievez et al, 2003) because they are generally rare or absent from feeds. The objective of this work was to use multivariate statistical analysis to explore the relationships between plant and microbial fatty acids in ingested herbage.