E-3A1 - Enteric Fermentation

Methane emissions from enteric fermentation are a significant source of greenhouse gases, primarily produced by the digestive processes in herbivorous livestock. This process occurs when microorganisms break down carbohydrates in the animal's digestive system into simpler molecules that can be absorbed into the bloodstream. The rate of methane emission is influenced by various factors including the animal's digestive tract structure, age, weight, and the quality and quantity of the feed consumed. Ruminants such as cattle and sheep, which have a specialized stomach compartment called the rumen for fermenting plant-based food, are the primary contributors. Conversely, non-ruminant and monogastric animals like pigs and horses emit considerably less methane due to less intensive fermentation processes in their digestive systems.

The production of methane is closely linked to feed intake, with higher intake generally leading to higher emissions. Factors like animal size, growth rate, and productive functions (e.g., milk or wool production) also affect methane outputs. To accurately estimate emissions, animals are categorised into subgroups based on species and production characteristics, with specific emission rates calculated for each subgroup. These calculations are crucial for developing accurate national emission inventories, as mandated by the IPCC guidelines, which emphasize considering only those animals under domestic management for emission estimates, excluding natural wild populations.

Categories¶

Enteric fermentation is broken down into the following categories in (Eggleston H.S. et al. 2006)¹

Eggleston H.S., Buendia L., Miwa K., Ngara T., and Tanabe K. 2006. “2006 IPCC Guidelines for National Greenhouse Gas Inventories.” IGES, Japan. https://www.ipcc-nggip.iges.or.jp/public/2006gl/index.html. ↩