Mongolia sustains a large population of small ruminants, with around 23 million sheep and an equal number of goats (National Statistics Office of Mongolia, 2025). These animals are vital for rural livelihoods, contributing to food security, household income, and traditional cultural practices (Mearns, 2004). Globally, livestock production is a major contributor to agricultural greenhouse gas (GHG) emissions, accounting for roughly 60% of the sector’s total output (FAO, 2021). Among GHG emissions, methane (CH₄) emissions from grazing ruminants represent about 29% of livestock-related GHG emissions, with 26.4% occurring in arid and semi-arid regions (Clark, 2017). Worldwide, sown pasture (SP) and native pasture (NP) supply nearly half of the feed consumed by grazing animals, supporting the livelihoods of an estimated 1.3 billion people (Belache et al., 2023; IPCC, 2019). Sheep, numbering around 1.2 billion globally, contribute approximately 6.4% of total enteric methane emissions from livestock (Patra, 2014a), making them the third largest ruminant source after cattle and buffalo (FAOSTAT, 2020). The sheep industry plays a role in advancing several United Nations Sustainable Development Goals (SDGs), and maintaining current production levels is considered desirable (Belanche et al., 2021). However, the predicted rise in global demand for meat (+73%) and milk (+58%) poses challenges to achieving CH₄ mitigation targets—estimated at up to 47% between 2010 and 2050—while sustaining productivity (Beauchemin et al., 2020). Meeting climate goals, such as limiting warming to 1.5 °C by 2030, will require mitigation strategies that do not compromise animal health, productivity, or welfare (Arndt et al., 2022). Accurate quantification of enteric CH₄ emissions across species, production systems, and regions is therefore essential. For sheep, however, comprehensive datasets covering different production environments remain scarce. The Intergovernmental Panel on Climate Change (IPCC) recommends estimating emissions using CH₄ conversion factors (Ym), which represent the fraction of gross energy intake lost as methane during enteric fermentation. The 2019 IPCC guidelines suggest a default Ym of 6.7% for all sheep categories and diets, with slightly adjusted values (7.0% or 6.5%) depending on dry matter intake (DMI) levels (Hammond et al., 2011). These estimates are based largely on New Zealand studies using high-quality forage diets (Swainson et al., 2018) and may not reflect the variability in diet quality, rumen fermentation, or animal class (e.g., lambs versus adults) in other regions (Moraes et al., 2014). Consequently, applying these default factors directly to grazing sheep in Mongolia could result in significant inaccuracies in national inventories or in cost-benefit analyses of mitigation measures.

Dry matter intake (DMI) is the most important predictor of enteric CH₄ production, as it shows a strong positive correlation with CH₄ emissions across all databases considered (Ellis et al., 2007). Consequently, forage quality is also a key predictor of greenhouse gas emissions, since it directly influences DMI (Belanche et al., 2023; Xie et al., 2023; Hammond et al., 2009; Patra, 2013). In Mongolia, animal performance is closely linked to both the quantity and quality of natural grasslands. For certain species, up to 98% of annual intake comes from native pasture. These grasslands, covering roughly 128.8 million hectares and hosting around 2,270 grass species (including 600 forage species), are distributed across six main zones:alpine tundra (3%) maintain taiga (4.1%) mountain steppe and desert steppe (25.1%), grass steppe (26.1), desert steppe (25.1) desert (14.5%) (Johnson et al., 2006; Amarsaikhan et al., 2023). Pasture growth is highly seasonal and climate-dependent, with new growth beginning as early as mid-April in forest steppe and steppe regions, and later in other zones. Grazing in early spring consists largely of senescent material, with fresh grass dominating intake from June to September (Munkhzul et al., 2021; Damiran et al., 2009). For roughly 200 days of the year, livestock rely primarily on senescent forage. Some areas are left ungrazed for haymaking or to serve as standing feed during winter (Togtokhbayar, 1995; Hu et al., 2023).

Over 90% of Mongolia’s sheep belong to the native “Mongol” breed, which is evenly distributed nationwide. Breeding farms in Bayantsagaan (Tuv aimag), Erdenedalai (Dundgovi aimag), and Hotont (Arkhangai aimag) maintain purebred and improved stock for distribution to more than 70 soums (Chadraabal, 2013; Sambuu, 2003; Nergui et al., 2011). This homogeneity creates an opportunity: even modest improvements in breeding and feeding practices could be scaled nationally, delivering significant mitigation gains while supporting pastoral livelihoods.

The present study aimed to quantify enteric CH₄ emissions from major rangeland ecosystems desert-steppe, steppe and mountain forest—in Mongolia using the IPCC Tier 2 methodology. This approach incorporates animal energy requirements based on liveweight, productivity, diet quality, and age sex categories of sheep.

This study was conducted in three specific locations in Mongolia. Khotont sum Arhkanhangai province represented forest steppe rangeland (47.369406, 102.473088°E), Bayantsagaan and Sergelen soum of Tuv province represented steppe rangeland (47.692664, 106.997982°E), Shivee-Govi soum of Gobi sumber province (46.157656, 108.545458°E)-represented rangeland sheep systems in semi-arid environments desert-steppe rangeland. For the selected sites, the use of seasonal weight change, energy partitioning calculation, and pasture quality analysis, combined with GPS-tracked locomotion data, ensures improved emission factor (EF) estimation relevant to extensive rangeland systems in the long-term studies.

Sheep across the study sites showed marked seasonal fluctuations. Autumn weights were consistently 11–12 kg higher than spring weights for adult males, 13–14 kg higher for adult females, 9–12 kg higher for two-year-olds, and 4–8 kg higher for lambs. These patterns reflect typical live weight dynamics under Mongolia’s rangeland conditions, where body reserves are accumulated during summer–autumn and mobilized during winter–spring. Reported organic matter digestibility (OMD) in Mongolian pastures generally varies between 61% and 67% (Nergui et al., 2011; Ariunsuren et al., 2025). However, the digestibility of winter forage is relatively low, around 48%, and and sheep rely on this grass for most of the year (approximately 170–200 days). This may contribute to higher greenhouse gas emissions. The chemical composition of the herbaceous vegetation, including organic matter, crude protein (CP), fiber fractions (NDF and ADF) was within the range typically reported for Mongolian pastures (Daalkhajav, 2009; Tserendash et al., 2011). Vegetation quality reached its peak in summer-autumm season, characterized by high CP and low NDF and ADF, in line with observations by Tserendash et al. (2011), who noted that alpine pasture plants mature in August, leading to decreased CP and increased fiber content due to a higher proportion of stems (Daalkhaijav and Lkagvajav, 1997). Consistent with trends observed in Mongolian forest steppe (Tserendash et al., 2011). Crude protein content was comparable to previous reports for forest steppe, steppe (Otgonjargal, 2012), and desert steppe (Togtohkbayar, 1995), and was similar to values reported for central mountainous regions (Daalkhaijav and Lkagvajav, 1997). The combination of moderately low CP and digestibility, along with elevated fiber levels, suggests a gradual decline in pasture quality from south to nort. Crude protein content was comparable to previous reports for forest steppe, steppe, and desert steppe, and similar to values reported for central mountainous regions. The combination of moderately low CP and digestibility, along with elevated fiber levels, suggests a gradual decline in pasture quality from south to north, consistent with trends observed in Mongolia s forest steppe. For grazing distance, no real difference was observed in the sheep, and they grazed at a distance of 4–7 km in summer and autumn, and 3.5–5 km in spring and winter (Figure 1). Therefore, when calculating the energy expenditure for movement, an average of 6 km was used in summer-autumn and 4 km in winter-spring. The grazing distance of the sheep flock, regardless of age and sex, was the same. Also, since the herders involved in the study did not milk their sheep, the grazing distance of the lambs was the same as that of the flock. Following Lin et al. (2011) we considered our GPS data sufficiently reliable despite the absence of differential correction. The average distance traveled by sheep in our study (6 and 4 km day⁻¹) was in the same range of relevant the 4.7–6.4 km day⁻¹ reported for sheep grazing Inner Mongolian steppes (Lin et al., 2011). Stocking pressure also played a role: densities of 2.5–7 sheep units (SU) per ha near Tsunkhul Lake and over 13 SU ha⁻¹ around camp sites, likely contributed to longer travel distances in July and August. Animut et al. (2005) demonstrated that increased grazing pressure can extend animal itineraries under comparable climatic conditions (Yoshihara et al., 2009). In our case, sheep often had to walk several kilometers each morning to reach high-quality forage, beyond the overgrazed areas close to their camp. Joly et al. (2013) reported average grazing distances of 5.1 km from camp in the Mongolian Gobi, which aligns with our observed mean radius of 6.75 km day⁻¹ and the 3.5–6.5 km range previously described for summer herding in Mongolia (Gendaram, 2011). Seasonal convergence in the daily travel distances of sheep is probably linked to the increasing forage availability from spring to early summer. According to Tsevegemed et al. (2019) the effective grazing distance for Mongolian Altai sheep and goats is approximately 10–11 km, which is influenced by the high altitude of the Altai Gobi and the availability of pasture plants. In mobile grazing systems, grazing area and associated energy expenditure are critical drivers of animal productivity and enteric methane emissions (Tsvegemed et al., 2018). Accordingly, the estimates derived from this study are not intended to represent national average conditions. In this context, reliance on IPCC Tier 1 default values constitutes a methodological limitation, as these values do not adequately capture the variability inherent in extensive and mobile grazing systems. Regarding net energy requirements, although seasonal and physiological effects were the main drivers of variation, differences among ecological zones were also evident. Forest–steppe sheep generally exhibited slightly higher NEm values compared with steppe or desert-steppe sheep of similar classes, likely reflecting the cooler and more variable climate as well as terrain-related increases in activity costs. For instance, gross energy intake (GE) of forest–steppe females during winter–spring averaged 21.37 MJ/day, which was comparable to steppe females (21.41 MJ/day) but slightly higher than desert-steppe females (20.61 MJ/day). This difference may be attributable to the availability of relatively better, yet more fibrous, forage in the forest–steppe, which increases energy expenditure for digestion and metabolism.

The estimated enteric methane (CH₄) emission factors for Mongolian sheep exhibited pronounced variation across agro-ecological zones (Figure 2), age classes, and sex. Adult females consistently showed higher emission factors than adult males, reflecting the greater nutritional demands associated with pregnancy and lactation. During the winter–spring season, emission factors ranged from 1.67 to 8.70 kg CH₄ head⁻¹ season⁻¹. Adult females exhibited the highest emissions, particularly in the steppe and desert-steppe zones (both 8.46 kg CH₄ head⁻¹ season⁻¹), while adult males showed the highest values in the steppe zone (8.70 kg CH₄ head⁻¹ season⁻¹). Young animals displayed intermediate emission levels (6.42–6.90 kg CH₄/head/season), whereas lambs produced substantially lower emissions (1.67–1.76 kg CH₄/head/season consistent with their lower body weight, reduced feed intake, and incomplete rumen development. In the summer–autumn season, emission factors declined across all animal categories and agro-ecological zones, ranging from 2.76 to 5.66 kg CH₄/head/season. Adult females again exhibited the highest emissions, particularly in the steppe zone (5.66 kg CH₄ head^-1 season⁻¹), followed by adult males (4.53–5.18 kg CH₄/head/season). Young animals and lambs maintained lower emission levels, consistent with their comparatively lower feed intake and metabolic demand. The overall reduction in methane emissions during summer–autumn likely reflects improved pasture quality, greater digestibility, and increased availability of green forage, which enhance animal productivity and reduce methane yield per unit of intake. Comparable patterns have been reported in small ruminant systems elsewhere, where physiological status strongly influences gross energy intake and subsequent methane production (Goopy et al., 2018; Gurmu et al., 2024; Lokupitiya, 2016). The elevated emissions observed in adult females emphasize the importance of accounting for reproductive status when developing emission factors, as reliance on a single default value may obscure substantial within-species variability. Similarly, age-related declines in emissions have been documented in Ethiopian and Kenyan smallholder sheep systems, where Tier 2 methodologies revealed that lambs contribute disproportionately less to total herd emissions than adult animals (Negussie et al., 2021; Wanjala et al., 2018). These findings highlight the necessity of differentiating age classes when constructing national greenhouse gas inventories, particularly in pastoral systems with high proportions of young animals. Clear spatial differences in emission factors were also observed among the desert-steppe, steppe, and forest-steppe zones. Overall, the steppe zone exhibited the highest methane emission factors, followed by the forest steppe and desert-steppe zones. This pattern likely reflects differences in pasture biomass, botanical composition, grazing intensity, and animal movement. Higher emissions in the steppe zone may be attributed to greater forage availability and intake, resulting in higher gross energy consumption and increased methane production. In contrast, the desert-steppe zone, characterized by limited biomass and poorer forage quality, exhibited lower emission factors, particularly during summer–autumn. Intermediate emission levels in the forest-steppe zone are consistent with its relatively favorable forage conditions and moderate climatic stress. This seasonal and spatial variability contrasts with observations from sub-Saharan Africa, where animals graze more diverse and protein-rich forages during the wet season, leading to greater fluctuations in methane emissions (Alemu et al., 2022; Goopy et al., 2018; Goopy et al., 2020). Collectively, these findings underscore the importance of developing region-specific emission factors rather than relying on global defaults that may not adequately represent local feeding ecology and production systems.

Several methodological and ecological factors must be considered when interpreting enteric methane (CH₄) emission estimates derived using the IPCC Tier 2 methodology under Mongolia’s nomadic pastoral systems. In extensive grazing environments characterized by high mobility, long-distance seasonal movements, and extreme continental climates, animal energy expenditure varies substantially in response to seasonal temperature fluctuations, forage availability, and grazing distance (IPCC, 2006; NRC, 2001; Goopy et al., 2018). However, the Tier 2 equations do not explicitly incorporate the additional metabolic costs associated with cold stress, thermoregulation, and long-distance movement, which are intrinsic features of Mongolian pastoral systems. Consequently, energy requirements and methane emissions may be under- or overestimated, particularly during the winter–spring season, when animals experience severe climatic stress and limited forage availability (Brosh et al., 2006; Fernández-Giménez et al., 2017; Alemu et al., 2022). A further limitation concerns the use of a fixed methane conversion factor (Ym), commonly set at 6.5% of gross energy intake (GEI). Accurate estimation of Ym ideally requires direct methane measurements and detailed assessment of feed digestibility, both of which vary markedly across seasons and rangeland types in mobile grazing systems (IPCC, 2006; Hristov et al., 2013; Moate et al., 2017). Previous studies have reported Ym values of 6.2% for housed sheep in Europe (Zhao et al., 2016), 7.5% for supplemented grazing dairy cattle in the Andes (Muñoz et al., 2018), and 6.9% for grazing beef heifers in temperate North America (Chaves et al., 2006). In contrast, grazing sheep in our study exhibited a higher CH₄ energy-to-GEI ratio (∼8.0%), exceeding the IPCC default range of 6.5% ± 1%. This likely reflects the combined effects of harsh climatic conditions, extensive mobility, and the relatively low digestibility and high ash content of Mongolian steppe forages (Yan et al., 2010; Rushing et al., 2019; Liu et al., 2020). To reflect the pronounced seasonal dynamics of Mongolian rangelands, we divided the year into two functional periods: a summer–autumn season characterized by green, actively growing pasture and positive live-weight change, and a winter–spring season marked by senescent forage, negative energy balance, and body weight loss. Accordingly, Ym values mean of 6.5%. While this approach captures broad seasonal contrasts, it remains a simplification and may not fully reflect short-term fluctuations in forage quality, intake, and animal metabolism that typify nomadic grazing systems. These limitations highlight the need for seasonally resolved, region-specific Ym values derived from direct field measurements.

Enteric methane (CH₄) emissions in Mongolian sheep exhibited clear variation across seasons, ecological zones, and animal categories (Figure 3). Emission factors were highest during the winter–spring season, when animals grazed senescent pasture and experienced body weight loss, and lowest in summer–autumn, when green forage supported higher intake and digestibility. Adult females consistently produced more CH₄ than males and young animals, reflecting higher energy requirements associated with reproduction and lactation. These findings highlight the importance of accounting for age, sex, and seasonality in estimating emissions under highly mobile pastoral systems.

We did not collect detailed productivity data, such as slaughter weight, wool yield, or milk production, and therefore any statements regarding emission intensity per unit of product should be considered preliminary. Nevertheless, productivity in Mongolian pastoral systems is strongly influenced by herd structure. Productivity-based emission intensity is shaped by herd structure. Meat is primarily obtained from 2–5-year-old males, whereas most females are retained for breeding until 7–8 years of age. All sheep produce wool, with average yields of 0.8–1.2 kg per year, while meat yield from market-age males averages 16–22 kg per animal (MOFA, 2025; Mongolian Institute of Animal Husbandry, 2011). Milk, although culturally and nutritionally important, is largely consumed locally and was excluded from emission intensity calculations. Given these production patterns, methane emissions per unit of marketed product are likely higher than in intensive systems. Targeted nutritional interventions for breeding females, such as providing higher-quality supplements during periods of high energy demand, could reduce methane emissions per unit of intake while maintaining productivity (Beauchemin and McAllister, 2007; Patra and Yu, 2013; Hristov et al., 2013).

These results underscore the limitations of generalized methane estimation frameworks, such as IPCC Tier 2, when applied to extensive grazing systems. Aggregating all sheep into a single emission factor may misrepresent national emissions, particularly in systems with strong seasonal and ecological variation. The estimated emission factors for Mongolian sheep (1.6–6.1 kg CH₄/head/year) are lower than IPCC (2019) defaults for small ruminants in developing countries (8–10 kg CH₄/head/year), reflecting lower energy intake and productivity under extensive grazing. While per-head emissions are lower, emission intensity per unit of product may be higher, emphasizing the need to quantify emissions relative to productivity. Overall, developing region- and season-specific emission factors that incorporate animal category, mobility, forage quality, and climatic stress is essential for improving the accuracy of national greenhouse gas inventories and informing realistic mitigation strategies in Mongolian pastoral systems.

Overall, these findings underscore the critical importance of developing region-specific emission factors for improving the accuracy of national greenhouse gas inventories in pastoral livestock systems. The results also emphasize the emission level vary systematically, as a function of physiological status, forage quality, and seasonal energy dynamics, highlighting the limitations of applying global default values in the Mongolian context. By incorporating location specific on diet digestibility, seasonal weight change, and reproductive status, this work provides a more robust basis for Monitoring, Reporting, and Verification (MRV) under the UNFCCC Enhanced Transparency Framework. Beyond the methodological refinement, the results also emphasize that targeted management, particularly improved ewe nutrition during pregnancy and lactation can play vital role in reducing methane intensity. These outcomes bring Mongolia’s capacity to design evidence-based mitigation strategies, while offering broader insights for rangeland-based livestock economies engaged in the Global Methane Pledge.