Enteric Methane Emission of Cattle Grazing Rangeland Ecosystems of South Eastern Kenya

Abstract

Large herds grazing degraded rangeland pastures are associated with enteric methane emission, contributing to Global Warming Potential (GWP). Kenya has large herds of ruminants grazing rangelands yet hardly are methane emissions and associated GWP quantified. This study estimated enteric methane emission and the GWP from cattle grazing in Makueni County, a rangeland ecosystem in Southeastern Kenya. Estimation applied the IPCC Tier II approach that incorporated seasonal differences in feed quality, dry matter intake and animal performance to provide improved methane emission factors (EFs). Data on cattle population, animal classes and their performance and animal activity for the year 2019 was obtained from the County livestock inventory reports while feed quality data was sourced from recently published literature. The resultant EFs were 47.1 kg year-1 for females> 2yrs; 27.2 kg year-1 for heifers 1-2 yrs; 46.5 kg year-1 for males> 2yrs; 32.9 kg year-1 for young males 1-2yrs; and 17.2 kg year-1 for calves< 1yr. These EFs were higher (7.7 to 14.9%) than those of Tier I for females> 2yrs, young males 1-2yrs and for calves< 1yr but lower (5.4 to 12.3%) for males> 2yrs and for heifers 1-2 yrs. The Tier II estimates were 4.4% higher than the estimates with Tier I approach for both total estimated enteric methane emission (9,279,526.80 vs 8,889,997 kg CH 4/year) and GWP (259,826,750.4 vs. 248,919,916 kg CO 2 eq). The results reflect uncertainty of EFs generated from Tier I approach, which necessitates development of region-specific EFs using data from local breeds of animals and feed resources. This will improve certainties of the enteric methane emissions and accuracy in reporting the Nationally Determined Contributions.