Comparison of Tier 1 and 2 methodologies for estimating intake and enteric methane emission factors from smallholder cattle systems in Africa: a case study from Ethiopia

Considering the potential environmental impact of livestock production and the significance of accurate estimation methods, it is crucial to assess the differences between various methodologies. The study compared the gross energy intake (GEI) and enteric methane (CH4) emission factors (EF = kg CH4/head/year) of cattle based on three methodologies: Intergovernmental Panel on Climate Change (IPCC) Tier 1, IPCC Tier 2 and a modified Tier 2 methodology based on Commonwealth Scientific and Industrial Research Organization (‘CSIRO’) Tier 2. Data were collected from smallholder mixed crop-livestock systems in the upper highland sub-humid to semi-humid (AEZ-1) and lower highland sub-humid to semi-humid (AEZ-2) zones of North Shewa, Ethiopia, corresponding to the beginning and end of spring, summer, and winter. The results revealed that the IPCC Tier 2 methodology estimated a 39% higher GEI (104 vs 74 MJ/ head/day) and a 51% higher implied EF (50 vs 33 kg CH4 /head/year) compared to the ‘CSIRO’ Tier 2 methodology. When compared to the IPCC Tier 1 default values, both the IPCC and ‘CSIRO’ Tier 2 EF estimates were 20–37% and 37–59% lower, respectively. Furthermore, all cattle categories exhibited variations in implied daily CH4 production across seasons. As all the GEI were estimated, it is not possible to determine which methodology is more accurate. Therefore, future research should compare predicted intakes and emissions with actual experimental data to ascertain the accuracy of the models.