Recovery of insoluble fibre fractions by filtration and centrifugation

Filtration and centrifugation methods were tested to study recovery of neutral and acid detergent fibre (NDF and ADF) and their N residues (NDFN and ADFN) in feeds, faeces and in vitro residues. Filtration of feeds and cow faeces were done in Porosity 2 (40–100 μm) sintered glass crucibles (SGC) or on flat papers (6 μm) or were centrifuged at 9000 × g for 5 min. Filtration of distillers dried grains with solubles and linseed cake by SGC clogged filters, unless sand was used as a filter aid. Fine feed fractions (<0.63 mm) gave relatively lower NDF recoveries by SGC filtration versus coarse fractions (0.63–1.5 mm). Centrifugation always resulted in higher recoveries of all the fibre fractions compared to SGC filtration. Paper filtration gave even higher recoveries for NDF and NDFN, compared to centrifugation. Digestibility of NDF in sheep gave lower estimates if feed and faecal NDF was estimated by paper filtration versus SGC filtration. The reason was a proportionally higher NDF recovery in faeces, as opposed to feed. Filtration on 6 μm papers should replace filtration in sintered glass crucibles to avoid serious losses of NDF, ADF and their respective N fractions.