Question

Under normal feeding conditions, methane forms what percent of the total gas produced in the rumen of cattle?

• A. 10 - 15%
• B. 15 - 20%
• C. 30 - 40%
• D. 20 - 30%

Hint:

Rumen Gas Composition:
$\text{CO}_2 = 60 - 65\%$.
$\text{CH}_4 = 30 - 40\%$. (Total daily production = $600 - 1000\text{ L/day}$).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Ruminal fermentation gas composition: anaerobic microbial fermentation in adult cattle produces 600--1000 L of gas daily, predominantly carbon dioxide (60--65%) and methane (30--40%).
Key Formula or Approach:
\[ \text{Rumen Gas Composition: } \text{CO}_2 (60 - 65\%) + \mathbf{CH}_4 \mathbf{(30 - 40\%)} + \text{N}_2 (2 - 5\%) + \text{H}_2, \text{O}_2, \text{H}_2\text{S} (< 1\%) \]

Step 2: Detailed Explanation:
In rumen physiology and gas dynamics:
- Ruminant forestomach fermentation generates enormous volumes of gas (up to $30 - 50\text{ litres/hour}$ in high-producing cows) eliminated continuously via the eructation reflex.
- The normal volumetric composition of rumen gas consists of:
1. Carbon Dioxide ($\text{CO}_2$): $60\% - 65\%$ (from microbial fermentation and bicarbonate saliva buffering).
2. Methane ($\text{CH}_4$): 30% to 40% (synthesized by methanogenic archaea like Methanobrevibacter ruminantium reducing $\text{CO}_2$ with $\text{H}_2$).
3. Nitrogen ($2-5\%$) and trace $\text{H}_2, \text{O}_2, \text{H}_2\text{S}$.

Step 3: Final Answer:
Therefore, methane forms 30 - 40% of total rumen gas, matching option (C).