Technical note: improved methodology for analyses of acid detergent fiber and acid detergent lignin

Our plain-English summary of Technical note: improved methodology for analyses of acid detergent fiber and acid detergent lignin, by E. Raffrenato, M.E. Van Amburgh (Journal of Dairy Science, 2011).

The study

• Authors: E. Raffrenato, M.E. Van Amburgh
• Journal: Journal of Dairy Science
• Published: 2011;94(7):3613-7
• Cited by: 31 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The objective of this study was to evaluate the methodology of the acid detergent lignin (ADL) assay in an effort to evaluate particle loss, improve repeatability, and decrease variation within and among samples. The original ADL method relied on asbestos as a filtering aid, but that was removed in 1989 with the mandate from the Environmental Protection Agency to eliminate asbestos in the environment. Furthermore, recent work on fiber methodology indicated that pore size in the Gooch sintered glass crucible (40-60 μm) was too large to trap all of the small particles associated with neutral detergent fiber (NDF) and acid detergent fiber (ADF). Thus, any loss of ADF could potentially result in a loss of ADL. Sixty forages including conventional and brown midrib corn silages, alfalfa silages and hays, mature grasses, early vegetative grasses, and 9 feces samples, were analyzed sequentially for ADF and ADL as outlined in the 1973 procedure of Van Soest except for the use of the asbestos fiber. A glass microfiber filter with a 1.5-μm pore size was chosen as a filtering aid because it met the criteria required by the assay: glass, heat resistant, acid resistant, chemically inert, and hydrophobic. To compare with the current ADF and ADL assays, the assays were conducted with either no filter or the glass filter inserted into crucibles, rinsed with acetone, and then according to the 1973 procedure of Van Soest. The samples analyzed covered a range from 18.11 to 55.79% ADF and from 0.96 to 9.94% ADL on a dry matter (DM) basis. With the use of the filter, the mean ADF values increased 4.2% and mean ADL values increased 18.9%. Overall, both ADF and ADL values were greater with the use of the glass microfiber filter than without, indicating that as the type of sample analyzed changed, use of the Gooch crucible without the filtering aid results in particle loss. The adoption of the use of a small pore size (1.5 μm) glass microfiber filter to improve filtration and recovery of ADF and ADL and to reduce variation in the ADL assay is recommended, especially when sintered glass bottom crucibles are used. These differences in recovery and repeatability have implications for other fiber and lignin methods, as well as for estimating the potential changes in digestibility of fibrous feeds and feed quality.

Copyright © 2011 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.

In plain English

This technical note was a laboratory methods study, not a study of asbestos exposure or health. It concerned how animal feeds are tested for fiber (acid detergent fiber, ADF) and lignin (acid detergent lignin, ADL). The authors explained that the original test procedure used asbestos fiber as a filtering aid, and that asbestos was removed from the procedure after the 1989 Environmental Protection Agency action. At Cornell University, the authors tested 60 forage samples (corn silages, alfalfas, grasses and straws) and 9 feces samples. Each sample was run in duplicate with and without a glass microfiber filter of 1.5-micrometer pore size placed inside the standard glass crucible. With the filter, mean ADF recovery increased 4.2% and mean ADL recovery increased 18.9%, and values were higher with the filter (P less than 0.05). For feces, the filter reduced the variation between repeat measurements. The authors noted that the filter made crucible weights about 0.05% more variable and could partly break down in sulfuric acid. The authors concluded that the filter is recommended to improve recovery in the test.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory methods comparison (technical note): feed and feces samples analyzed with and without a glass microfiber filter in the crucible
• Who was studied: 60 forage samples (conventional and brown midrib corn silages, alfalfa silages and hays, mature grasses, early vegetative grasses) and 9 feces samples, analyzed at Cornell University, Ithaca, NY; no people were studied
• Exposure: No human asbestos exposure was studied. Asbestos fiber had been the filtering aid in the original lab procedure. This study compared no filtering aid with a 1.5-micrometer glass microfiber filter (Whatman 934-AH) as a replacement.
• Main results:
  • Across all samples, using the glass microfiber filter increased mean ADF recovery by 4.2% and mean ADL recovery by 18.9%
  • Both ADF and ADL values were greater with the filter than without it (P less than 0.05)
  • Differences in measured ADL were lowest for alfalfas, intermediate for grasses and wheat straw, and highest for immature grasses, corn silages and feces
  • Repeatability with the filter was similar to repeatability without it (P greater than 0.05) for grasses, brown midrib corn silages, alfalfas and immature grasses
  • For feces samples, the filter lowered the repeatability standard deviation from 0.17 to 0.06% for ADF and from 0.23 to 0.06% for ADL (P less than 0.05)
  • The filter also reduced the variation in ADL measurement for wheat straws and conventional corn silages
  • Crucible weight loss through the procedure averaged 0.02% and did not differ between crucibles with and without filters
• The authors' conclusion: The authors concluded that the 934-AH glass microfiber filter is recommended to increase recovery in the sequential ADF and ADL procedure, and that it brings the method back in line with the original AOAC ADL method of Van Soest (1973)
• Limitations the authors state:
  • Inserting the filter increased the variation in crucible weight by about 0.05% with hot weighing, so more care and time are needed when weighing
  • The filter can partly degrade during the 72% sulfuric acid step. The authors stated this did not affect results, but the supporting data were not shown.
  • The water-absorbing (hygroscopic) potential of the crucibles was not measured

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