Substance Inhibiting Rumen Metabolism

Rumen metabolism is inhibited in the presence of:

Correct Answer: Oxygen

Rumen metabolism is inhibited in the presence of Oxygen (O₂) because the majority of rumen bacteria are obligate anaerobes — they cannot survive or function in the presence of oxygen.

Rumen Microbial Characteristics

• Most rumen bacteria: Gram-negative and obligate anaerobes → inhibited by O₂.
• Exception: Lactic acid-producing bacteria are facultative anaerobes; they are attached to the ruminal wall because a small amount of O₂ is present in the periphery.

Rumen Redox Potential

• The rumen maintains a highly reduced (anaerobic) environment.
• Liquid phase redox potential: approximately −350 mV (highly negative = strongly reducing).
• This negative redox environment is essential for anaerobic microbial fermentation.

Rumen Microbial Population (per ml rumen liquor)

• Bacteria: 10¹⁰⁻¹¹ (highest)
• Bacteriophage: 10⁹
• Protozoa: 10⁶
• Fungi: 10³ (lowest)