Enteric methane emission factors for sheep in Mongolian extensive grazing systems: a Tier 2 approach

Methane emissions from livestock are a significant contributor to agricultural greenhouse gas outputs, yet region-specific emission factors are often lacking for nomadic pastoral systems. This study determined annual enteric methane emission factors for sheep across three major agro-ecological zones of Mongolia: Desert-steppe, steppe, and forest-steppe, considering animal sex and age categories. Animal performance data were collected for adult males (>3 years), adult females (>3 years), young sheep (1–2 years), and lambs (<1 year). According to the IPCC Tier 1 methodology, the default emission factor for adult sheep is 5 kg CH 4 /head/year, while lamb values are estimated at approximately 2 kg CH 4 /head/year. Nevertheless, these generalized values fail to capture country-specific differences in animal productivity, diet quality, seasonal feed availability, and grazing management, thereby introducing significant uncertainty into national greenhouse gas inventories. Results showed that females consistently exhibited higher emission factors than males, with values ranging from 6.0 to 6.1 kg CH 4 /head/year, compared to 5.40–5.45 kg CH 4 /head/year for males. Young sheep emitted between 4.3 and 4.9 kg CH 4 /head/year, while lamb emissions were lowest at 1.6–1.8 kg CH 4 /head/year. These findings provide updated, region-specific methane emission factors for Mongolian sheep, supporting the refinement of national greenhouse gas inventories and climate change mitigation strategies.