MEASURING DETERGENT FIBRE AND INSOLUBLE PROTEIN IN CORN SILAGE USING CRUCIBLES OR FILTER BAGS

Authors: FERREIRA, GONZALO - UNIV. OF WISCONSIN-MADISO; Mertens, David

Submitted to: Animal Feed Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2006
Publication Date: 2/15/2007
Citation: Ferreira, G., Mertens, D.R. 2007. Measuring detergent fibre and insoluble protein in corn silage using crucibles or filter bags. Animal Feed Science And Technology. 133(3-4):335-340.

Interpretive Summary: Fiber and insoluble protein are important feed components that affect dairy cow health and performance. If we feed diets too high in fiber, the bulk associated with high-fiber diets restricts a cow's feed intake and limits her milk production. If we feed energy-dense diets that are too low in fiber, the cow's digestion suffers and she can become sick because she does produce enough saliva during chewing to keep her stomach from becoming too acidic. Insoluble protein is important because it can escape the destructive fermentation in the cow's stomach and become a source of amino acids when absorbed in her small intestine. As the level of milk production rises, it becomes more difficult to design diets for dairy cows that provide adequate fiber and protein. Thus, it becomes more important to know the content of fiber and insoluble protein in feed ingredients so that the optimum diet can be formulated for cows to maintain their health and productivity. Typically fiber is extracted in detergent solutions and collected in crucibles that have porous disks in the bottom that allow the extraction solution to be removed by filtration. To measure the insoluble protein, the extracted fiber must be scraped from the crucible and analyzed for protein. An alternative technique for measuring fiber and insoluble protein extracts the feed in a porous bag similar to a tea bag using the same detergent solution in a pressurized chamber. Measuring insoluble protein using this system is relatively easy because the protein content of the residue and bag can be determined without transferring it to another container. In this research we compared several methods of measuring fiber and insoluble protein in corn silage, an important feed for dairy cows. Both starch and protein can contaminate fiber in corn silage, so three different methods of measuring neutral detergent fiber (NDF) were compared using both crucibles and filter bags. The three methods were neutral detergent with sodium sulfite to remove all but the most insoluble protein, neutral detergent with amylase enzyme to help remove the starch, and neutral detergent with both amylase and sodium sulfite. Fiber analyses were similar for both crucible and filter bags when neutral detergent solution was used with both amylase and sodium sulfite. Using amylase but not sulfite increased fiber and insoluble protein values for both crucibles and filter bags. When amylase was not used, the filter bag system obtained much higher fiber values than the crucible. We demonstrated that both amylase and sodium sulfite are needed to accurately measure fiber in corn silage. We concluded that the filter bag method gives similar results to the original crucible method for fiber and insoluble protein when both amylase and sodium sulfite are used during extraction.

Technical Abstract: Different methods exist for the determination of fibre concentration in feeds. To determine whether fibre recovery and the contamination of NDF 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 (55ºC 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), a-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 higher (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 a-amylase was not used. For tCRUC, NDF and NDR concentrations were similar (456 g/kg), although filtration of fibre residue after extraction without a-amylase was difficult. Detergent insoluble CP 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, insoluble CP was greater for NDR determined with out 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 insoluble CP 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.