Which statement correctly describes the relationship of NDF and ADF to intake and digestibility?

Which statement correctly describes the relationship of NDF and ADF to intake and digestibility?

• A. ADF measures lignin and cellulose; NDF measures soluble sugars.
• B. NDF measures total cell wall components; ADF measures lignin and cellulose; higher NDF lowers intake; higher ADF lowers digestibility.
• C. NDF measures moisture content; ADF measures ash.
• D. NDF measures crude protein; ADF measures energy.

Answer: (B)

NDF and ADF relate to intake and digestibility because they reflect different fiber fractions in feed. NDF measures total cell wall components (hemicellulose, cellulose, and lignin), which contribute to the bulk of plant material. Because animals regulate intake to avoid excessive rumen filling, higher NDF means more bulk and typically lower voluntary intake. ADF measures the more resistant portion of the cell wall—primarily cellulose and lignin. Lignin is largely indigestible, and higher ADF indicates less digestible, energy-rich material, so digestibility and energy availability decrease as ADF increases. Therefore, the statement that NDF measures total cell wall components and ADF measures lignin and cellulose, with higher NDF lowering intake and higher ADF lowering digestibility, best describes their roles.

NDF and ADF relate to intake and digestibility because they reflect different fiber fractions in feed. NDF measures total cell wall components (hemicellulose, cellulose, and lignin), which contribute to the bulk of plant material. Because animals regulate intake to avoid excessive rumen filling, higher NDF means more bulk and typically lower voluntary intake. ADF measures the more resistant portion of the cell wall—primarily cellulose and lignin. Lignin is largely indigestible, and higher ADF indicates less digestible, energy-rich material, so digestibility and energy availability decrease as ADF increases. Therefore, the statement that NDF measures total cell wall components and ADF measures lignin and cellulose, with higher NDF lowering intake and higher ADF lowering digestibility, best describes their roles.