Calculation of new enteric methane emission factors for small ruminants in western Kenya highlights the heterogeneity of smallholder production systems

Context: African livestock play a critical role in food security and the wider economy, while accounting for >70% of African agricultural greenhouse gas emissions. Accurate estimates of greenhouse gas emissions from livestock are required for inventory purposes and to assess the efficacy of mitigation measures. While there is an increasing number of studies assessing methane (CH$_{4}$) emissions of cattle, little attention has been paid to small ruminants (SR).
Aims: Enteric CH$_{4}$ emissions were assessed from 1345 SR in three counties of western Kenya to develop more accurate emission factors (EF) for enteric CH$_{4}$ from sheep and goats.
Methods: Using on-farm animal activity data, feed samples were also analysed to produce estimates of feed digestibility by season and region. The combined data were also used to estimate daily CH$_{4}$ production by season, location and class of animal to produce new EF for annual enteric CH$_{4}$ production of SR.
Key results: Mean dry-matter digestibility of the feed basket was in the range of 58–64%, depending on region and season (~10% greater than Tier I estimates). EF were similar for sheep (4.4 vs 5 kg CH$_{4}$/year), but lower for goats (3.7 vs 5 kg CH$_{4}$/year) than those given for SR in developing countries in Intergovernmental Panel on Climate Change (Tier I) estimates.
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Conclusions: Published estimates of EF for SR range widely across Africa. In smallholder systems in western Kenya, SR appear to be managed differently from cattle, and EF appear to be driven by different management considerations.
Implications: The findings highlighted the heterogenous nature of SR enteric emissions in East Africa, but also suggested that emissions from SR are quantitatively less important than other estimates suggest compared with cattle.