Model-based estimation and comparison of enteric methane emissions to assess model outcomes in South Asian cattle...

South Asia hosts over 270 million cattle raised under diverse low-input production systems, yet enteric methane (Ent_CH4) emissions in the region are often estimated using models developed for temperate, high-productivity systems. This study compared eight commonly used enteric methane prediction models - five based on dry matter intake (DMI) (IPCC_DMI, Ribeiro_DMI, Patra_DMI, ¹Alam_DMI, ²Alam_DMI) and three based on gross energy intake (GEI) (IPCC_GEI, Ribeiro_GEI, Patra_GEI) - using standardised feeding trial data from India, Pakistan and Bangladesh. Data were extracted from 91 published feeding trials covering 1684 cattle of different breeds, physiological states and yield levels. The Intergovernmental Panel on Climate Change (IPCC) models overestimate emissions by approximately 7-28% compared with the Alam models across different factors, for example, countries, breed and lactating status. Significant variation was observed across countries, with Pakistani cattle showing the highest predicted emissions compared to India and Bangladesh, driven by greater body weight and feed intake. Breed-wise comparisons revealed consistently higher emissions from Holstein Friesians than from indigenous and Sahiwal cattle. The IPCC models consistently overestimated methane compared with tropical-calibrated models. GEI-based models showed less variation than DMI-based models. Overall, the study highlights large discrepancies among models and demonstrates the importance of using region-specific or tropical-calibrated equations for robust Ent_CH4 estimation in South Asian cattle. These findings provide an evidence base for improving national greenhouse gas inventories and methane mitigation planning in tropical livestock systems.