Impact of alternative methods on measurement of NDF compared to the official method

Authors: Hall, Mary Beth

Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/20/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Neutral detergent fiber (NDF) is an important metric of fiber in dairy cattle nutrition used in diet formulation. An empirical method, NDF is defined by the procedure used to measure it. The Association of Official Analytical Chemists Official Method 2002.04 is the current definitive method (AOAC) for NDF treated with amylase (aNDF). It is performed on dried samples ground through the 1-mm screen of a cutting mill with refluxing and then filtration through coarse porosity Gooch crucibles without or with a filtration aid. Method variants with modifications such as grinding materials through the 1-mm screen of an abrasion mill or using different filtration or extraction systems must give analytical values equivalent to AOAC or they do not measure aNDF. Comparisons must rigorously adhere to recommended procedures. Extraction of samples and recovery of the residue on filters may be affected by method variants. Grinding though a 1-mm screen with an abrasion mill versus a cutting mill gives a finer particle size, possibly allowing greater extraction or escape. Extracted particles may pass through filters when liquid carrying the particles flows through; this is affected by a filter’s particle retention value (PR). Performance of filters and filtration methods must be assessed within the procedure used. Simultaneous extraction and filtration used in filter bag systems gives particles the time of extraction and rinsing to interact with the filter, whereas decanting, rinsing, and soaks give less time in other filtration systems. In a limited study, filter bags gave values closer to AOAC when bags with finer PR were used. Crucibles that are plugged or degraded can also deviate from AOAC. In a limited study, best agreement between AOAC and aNDF method variants was achieved with the 1-mm screen cutting mill grind. The 1-mm abrasion mill grind produced more aNDF% results that were lower than AOAC but with fewer differences when filter PR was smaller. The use of filters that retain finer particles could be explored to improve comparability of NDF method variants and grinds with AOAC. Further evaluation with an expanded set of materials is needed. Key words: fiber, feed analysis, methods