Detergent fiber measurements show that NDF reflects cell wall content affecting intake, and ADF reflects lignin and cellulose affecting digestibility.

• A. NDF relates to lignin concentration while ADF relates to lignin and cellulose; both directly determine energy density.
• B. NDF measures soluble sugar content; ADF measures protein content.
• C. NDF affects intake, and ADF affects digestibility; higher contents reduce intake and digestibility.
• D. NDF and ADF are not related to forage digestibility.

Answer: (C)

Detergent fiber measurements separate two aspects of the plant cell wall that matter for how ruminants use forages. Neutral detergent fiber reflects the total cell wall content (the structural parts like cellulose, hemicellulose, and lignin), which drives rumen fill. When NDF is high, the forage takes up more space in the rumen, slows passage, and animals eat less. Acid detergent fiber, on the other hand, targets cellulose and lignin; lignin is largely indigestible and both components decrease overall digestibility as their proportion rises. So, higher NDF mainly limits intake, and higher ADF mainly lowers digestibility. That’s why the statement that NDF affects intake and ADF affects digestibility, with higher contents reducing both intake and digestibility, is the best fit. The other options misstate what NDF and ADF measure or their effects on digestibility.