Methane emission factors and carbon fluxes from enteric fermentation in cattle of Nepal Himalaya

Abstract

This study presents a first estimate of the country-specific enteric methane (CH₄) emission factors (EFs) and the net CH₄ fluxes for the local and improved cattle breeds (LCB and ICB) in Nepal using the IPCC Tier 2 methodology. The country-specific herd structure, morphological and feed characteristics data of cattle were collected from the field survey. In LCB, adult males had the highest mean live body weights (BWs) ranging from 222 ± 42 kg in the Hill to 237 ± 36 kg in the Plain region, while for improved cattle, adult females had the highest BW of 334 ± 45 kg in the Hill to 308 ± 38 kg in the Plain regions. Weight gains of ICB were higher than the LCB. Local calves gained BWs of 97 ± 20 g day^-1, while improved calves gained a weight of 202 ± 41 g day^-1. The CH₄ EFs ranged from 13 ± 3 to 46 ± 9 kg CH₄ head^-1 yr^-1 for different age-groups of the LCB, while for the ICB, the EFs ranged from 14 ± 3 to 75 ± 15 kg CH₄ head^-1 yr^-1. Overall, the EFs were 33 ± 7 and 46 ± 9 kg CH₄ head^-1 yr^-1 for LCB and ICB, respectively. The estimated enteric EFs of cattle in the Hill and Plain regions were not statistically different (p > 0.05), but a significant difference existed between the breeds (LCB and ICB; p < 0.05). The net CH₄ flux was 254 ± 51 Gg yr^-1 from enteric fermentation in cattle of Nepal using the country-specific EFs, about 15% higher than using the default EFs (221 ± 66 Gg yr^-1). We underline that the emission estimation, deploying the country-specific EFs, will be more accurate, contributing to reduce the uncertainties in the national GHG inventories and supporting the mitigation actions.

Keywords: CH(4) fluxes; Emission factor; Enteric fermentation; Greenhouse gas; Gross energy intake.