Question

Which one of the following is a natural indicator to measure digestibility in animals?

• A. Carmine red
• B. Chromic oxide
• C. Ferric oxide
• D. Lignin

Hint:

Digestibility Indicators:
Natural Internal Markers = LIGNIN, Silica, Indigestible ADF (iADF).
Synthetic External Markers = Chromic Oxide ($\text{Cr}_2\text{O}_3$), Titanium dioxide, Carmine Red.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Indicator (marker) methods in digestion trials: natural internal indigestible plant markers vs synthetic external non-absorbable markers.
Key Formula or Approach:
\[ \text{Nutrient Digestibility (\%)} = 100 - \left[ 100 \times \frac{\% \text{ Indicator in Feed}}{\% \text{ Indicator in Faeces}} \times \frac{\% \text{ Nutrient in Faeces}}{\% \text{ Nutrient in Feed}} \right] \]

Step 2: Detailed Explanation:
Digestibility markers (indicators) classification:
1. Internal (Natural) Indicators: Natural chemical constituents of the forage feed that are completely indigestible, non-toxic, and flow uniformly through the gut. Key examples include Lignin (Acid Insoluble Lignin AIA), Silica, and Indigestible Acid Detergent Fiber (iADF).
2. External (Synthetic) Indicators: Inert foreign substances intentionally added to feed in known amounts, such as Chromic Oxide ($\text{Cr}_2\text{O}_3$), Ferric Oxide, Carmine Red, and Titanium Dioxide ($\text{TiO}_2$).
Therefore, Lignin is the natural internal indicator.

Step 3: Final Answer:
Therefore, Lignin is a natural indicator to measure digestibility, matching option (D).