IPCC Tier 2 methodology systematically underestimates dry matter intake and enteric methane emissions in indigenous Tanzanian cattle fed supplemented diets

Livestock contribute approximately 30% of anthropogenic methane (CH 4 ) emissions, making accurate quantification essential for national greenhouse gas (GHG) inventories and mitigation strategies. The Intergovernmental Panel on Climate Change Tier 2 methodology estimates dry matter intake (DMI) from animal energy requirements and then applies a CH 4 conversion factor to calculate enteric emissions. However, its intake prediction equations were parameterized primarily from temperate livestock systems, raising questions about accuracy in African production contexts. This study evaluated IPCC tier 2 accuracy for estimating DMI and daily methane production (DMP) in Boran and Tanzanian Shorthorn Zebu (TSHZ) cattle fed three supplemented hay-based diets: ad libitum hay plus 60% (HayC60), 80% (HayC80), or 100% (HayC100) of ad libitum concentrate. DMP was estimated by two approaches: Tier2intake (using directly measured DMI) and Tier2IPCC (using IPCC equation-predicted DMI). Measured DMI exceeded IPCC-predicted DMI by 21%–34%, varying by breed and treatment. Correspondingly, Tier2intake yielded substantially higher DMP estimates than Tier2IPCC: 91 g vs. 70 g CH 4 /head/day for Boran, and 76 g vs. 55 g CH 4 /head/day for TSHZ (p < 0.001). These discrepancies exceeded the IPCC default uncertainty range of ±20%, indicating systematic underestimation when Tier 2 is applied to indigenous African cattle. These findings have important implications for national GHG inventory accuracy and the design of evidence-based mitigation strategies for African livestock systems.