Why are roughages usually low in energy?

Why are roughages usually low in energy?

• A. High moisture
• B. High cell wall content
• C. Low fiber
• D. High starch

Answer: (B)

Roughages are low in energy mainly because they have a lot of structural material in their cell walls, i.e., high fiber content. The main components of plant cell walls—cellulose, hemicellulose, and especially lignin—are much less digestible than the nonstructural carbohydrates found in concentrates. Even in ruminants, where microbes can ferment some fiber, the energy yield per kilogram of dry matter from these fibers is substantially lower than from starches or sugars. The result is a lower energy density in roughages. Moisture level isn’t what drives the low energy; energy density is about what the dry matter actually provides. Low fiber would raise energy density, and high starch would also raise it, so those options don’t describe why roughages tend to be energy-poor.

Roughages are low in energy mainly because they have a lot of structural material in their cell walls, i.e., high fiber content. The main components of plant cell walls—cellulose, hemicellulose, and especially lignin—are much less digestible than the nonstructural carbohydrates found in concentrates. Even in ruminants, where microbes can ferment some fiber, the energy yield per kilogram of dry matter from these fibers is substantially lower than from starches or sugars. The result is a lower energy density in roughages.

Moisture level isn’t what drives the low energy; energy density is about what the dry matter actually provides. Low fiber would raise energy density, and high starch would also raise it, so those options don’t describe why roughages tend to be energy-poor.