Measuring detergent fibre and insoluble protein in corn silage using crucibles or filter bags

Different methods exist for the determination of fibre concentration in feeds. To determine, whether fibre recovery and the contamination of fibre by nitrogenous compounds are altered, we measured fibre concentrations in a diverse set of corn silages using three method modifications and two extraction/filtration systems. Thirty-three corn silages, obtained from a commercial feed analysis laboratory, were dried (55°C for 24 h) and ground to pass through a 1-mm screen of a cutter mill before analysis. All samples were extracted in neutral detergent with the inclusion of sodium sulphite (neutral detergent fibre or NDF), α-amylase (neutral detergent residue or NDR) or both (amylase-treated neutral detergent fibre or aNDF), and using either Gooch crucible (CRUC) or filter bag (FBAG) systems. The aNDF method obtained the lowest and similar average fibre concentrations for both CRUC and FBAG (433 and 433 g/kg, respectively). Fibre concentration of NDR was greater (456 and 449 g/kg for CRUC and FBAG, respectively) than aNDF. Fibre concentration was greater for NDF (473 g/kg) than for NDR and aNDF (449 and 433 g/kg, respectively) when using FBAG. Poor extraction occurred for FBAG when α-amylase was not used. For CRUC, NDF and NDR concentrations were similar (456 g/kg), although filtration of fibre residue after extraction without α-amylase was difficult. Neutral detergent insoluble crude protein (ICP) was similar for NDF and aNDF, and slightly greater FBAG than for CRUC systems (8.4 and 9.6 g/kg, respectively). With both FBAG and CRUC, ICP was greater for NDR determined without sulphite (12.5 and 14.2 g/kg, respectively) than for aNDF (8.6 and 9.7 g/kg, respectively). The lower fibre concentration for aNDF method was attributed to less starch contamination when compared to NDF and to less protein contamination and possibly to extraction of phenolic compounds when compared to NDR. Concentration of acid detergent fibre (ADF) was greater for CRUC than for FBAG, although this difference was minimal (266 and 261 g/kg, respectively). Acid detergent ICP was similar for CRUC and FBAG systems and averaged 4 g/kg. We observed that amylase and sulphite affect the measurement of NDF concentration in corn silage. It is crucial that authors and laboratories accurately describe how they measure NDF and clearly indicate by acronym the method they used. Although the extraction/filtration system did not affect the determination of NDR and aNDF, the FBAG system generated higher NDF concentrations for corn silage when amylase is not used.