| Sumario: | Methane (CH4) is the primary greenhouse gas (GHG) emitted by livestock in the agricultural sector, and accounts for 32% of all global anthropogenic GHG emissions. As part of their commitment to the Paris Agreement and the United Nations Framework Convention on Climate Change, Kenya has pledged to reduce 32% of its national GHG emissions by 2030 relative to the business-as-usual (BAU) scenario, where enteric CH4 is the largest source of emissions, with dairy cows being a significant contributor. To estimate enteric methane emissions for national GHG inventories, the daily gross energy intake (GEI) of individual animals is calculated and then multiplied by a CH4 conversion factor (Ym).
According to the Intergovernmental Panel on Climate Change (IPCC) Tier 2 methodology, key factors to estimate livestock GHG emissions include ruminant diets containing 18.45 MJ of gross energy (GE) per kg of dry matter (DM) and methane energy content of 55.65 MJ/kg. A standard Ym value of 6.5-7.0% corresponding to 19.8 g CH4/kg DM intake has been adopted for Kenya's latest inventory of GHG emissions from dairy cattle. These default values are based on data collected from the Global North representing the livestock systems found there, but they have been implemented by many Sub-Saharan countries in their national GHG inventories, although the conditions in local systems might be different. This highlights an urgent need for local data to improve the accuracy of national inventories for SSA countries and to support governments in making informed decisions to meet mitigation targets.
This study measured Ym (CH4 kg-1 DMI) of lactating cows fed diets based on local feed resources under semi-intensive conditions. Nine crossbred heifers were included in a complete changeover design (3x3 Latin Square) with three experimental feeding periods of 20 days each (14 days of adaptation followed by six days of sample collection). Samples were collected over three days for DM intake (DMI) and diet digestibility, and an additional three-day period in a respiratory chamber to measure enteric CH4 emissions. Three experimental diets (0.88:0.12 forage-to-concentrate ratio on a DM basis) varying in crude protein (CP; % DM basis) and digestible energy contents were formulated as: 'Low'- (CP: 10%, DE: 59.5%), 'Medium'- (CP: 12%, DE: 61%), and 'High'-quality (CP: 14%, DE: 62.5%) diets. The Medium-quality diet served as the baseline for diets' formulation as reported in Kenya's GHG inventory and diets were aimed to be representative of local feed resources. The trial is ongoing and will last until February 2025. This study will contribute to the understanding of how diet compositions in semi-intensive dairy systems can influence enteric CH4 emissions to obtain a more reliable Ym factor under Kenyan conditions.
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