Review: Comparative methane production in mammalian herbivores

Area of Science:

• Animal Science
• Microbiology
• Environmental Science

Background:

• Methane (CH4) production is a natural byproduct of fiber digestion in herbivore gut microbiota.
• Previous research suggested CH4 emissions varied significantly with body mass and digestive strategies.

Purpose of the Study:

• To compile and analyze in vivo CH4 measurements across diverse mammalian herbivore species on forage-only diets.
• To investigate the relationship between CH4 production, body mass, diet intake, and digestive physiology.
• To identify factors influencing interspecific variation in CH4 emissions.

Main Methods:

• Compilation of existing literature data and new measurements of in vivo CH4 production.
• Analysis of CH4 emissions relative to dry matter (DM) intake, gross energy intake, body mass, digesta retention time, and gut capacity.
• Comparison of CH4 yields across ruminants, non-ruminants, foregut fermenters, and hindgut fermenters.

Main Results:

• Absolute CH4 emissions scaled linearly with DM intake, not body mass.
• CH4 yields did not significantly vary with body mass across species.
• Ruminants and non-ruminants, foregut and hindgut fermenters showed no consistent dichotomy in CH4 intensity.
• Equids, macropods, and rabbits exhibited unusually low CH4 production.
• Intraspecific variation in CH4 yield per digested fiber suggests differences in gut microbiota functionality.

Conclusions:

• CH4 physiology is not limited by herbivore body size.
• Host-specific factors beyond digestive anatomy and rumination influence CH4 production.
• Variation in gut microbiota, including methanogens, plays a key role in CH4 production.
• The evolutionary benefit of methanogens for host species remains an open question.