The filter bag versus the conventional filtration technique for the determination of crude fibre and Van Soest cell wall constituents

To determine crude fibre (CF), NDF, ADF and ADL, the conventional technique (CT), using filter crucibles, was compared with the filter bag technique (FBT). The mean CF content of 56 forages and concentrates was slightly, but significantly lower (P<0.001) with FBT than with CT (144 vs 138 g·kg^-1 DM). The two techniques were highly correlated (0.996) and FBT had better repeatability. The mean CF content of 28 faeces samples was similar for both techniques, but repeatability with FBT was worse. The latter was greatly improved by reducing the sample weight from 1 to 0.5 g. For NDF a comparative study was done with 10 non-starchy feeds, 14 starchy feeds, as well as with 28 feed residues from in sacco incubations. To obtain similar values with FBT as with CT, it is recommended to use a sample weight of 0.5 g and to add for all starch containing samples 12 ml of an α-amylase solution, equally spread over the digestion and the first two rinsing periods. For ADF of 11 feeds the correlation between the two techniques improved from 0.993 to 0.997 when 0.5 instead of 1.0 g sample was incubated and repeatability was clearly better for the FBT. For ADL of 12 feeds, after sequential analysis of NDF and ADF, the FBT showed excellent precision and no significant difference with the CT.