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Methane (CH 4 ) emission estimations for cattle in Sub-Saharan Africa (SSA) reflect limited production levels and diets that are high in cellulose forage. However, data on these livestock systems is lacking for their accurate evaluation. To provide guidance for climate change mitigation strategies in Senegal, it is necessary to obtain reliable estimates of CH 4 emissions from Ndama cattle reared in grazing systems, which is the predominant cattle system in the country. The objective of this study was to determine the annual methane emission factor (MEF) for enteric fermentation of Ndama cattle following the IPCC Tier 2 procedure. Our estimated annual MEF at the herd scale was 30.8 kg CH 4 /TLU (30.7 kg CH 4 /head/yr for lactating cows and 15.1 kg CH 4 /head/yr for other cattle). These values are well below the default IPCC emission factor (46 and 31 kg CH 4 /head/yr for dairy and other cattle, respectively) proposed in the Tier 1 method for Africa. Our study showed that feed digestibility values differ with season (from 46 to 64%). We also showed that cattle lose weight and adapt to lower feed requirements during the long dry season, with a resulting major reduction in methane emissions. The results of this work provide a new framework to re-estimate the contribution of grazing systems to methane emissions in Africa.

In Northern Senegal, traditional cattle management systems (TRAD) which depend on natural forages coexist with intensified systems (INT) which rely on periodic supplementation with crop residues and local concentrates. This study aims to estimate the effects of seasons and management systems on the methane emissions of Gobra zebu, in relation to the diet's chemical composition and feed intake. Six Gobra zebu cows per management system were individually monitored over 10 months, diet and faeces were sampled each season and their chemical composition and dry matter intake (DMI) were predicted by near infrared spectroscopy. Each diet was fermented in vitro to assess methane production and volatile fatty acid concentration. The DMI and digestible organic matter intake (DOMI) decreased (P < 0.0001) during the dry seasons for both systems in the same range, but INT improved the crude protein of the diets (P < 0.0001). Enteric methane production (mmol.g -1 dry matter) was lower for TRAD than INT, except during the rainy season when TRAD cows experienced a higher increase (P = 0.002). The methanogenic potential (methane production in vitro × DMI) varied with the seasons and the system with more accentuated variations for TRAD (P < 0.0001). Methanogenic potential shows true reflection of the effects of the seasons and management systems. The results highlight that enteric methane emissions varied with seasonal changes and that intensifying the diet induced no mitigating effect.

Given the projected growth of methane emission by ruminants in developing countries, there is a clear need for reliable estimates of their contribution to greenhouse gas emissions. Existing studies have rarely considered sheep and goats. The objective of this study was to predict enteric fermentation methane emission factors (EFs) for Djallonké sheep and West African Dwarf goats, following the 2006 IPCC Tier 2 methodology. Estimated enteric methane emission factors, expressed per head of animal per year, were 2.3 kg CH 4 and 2.0 kg CH 4 for sheep and goats species, respectively. Compared with the generic Tier 1 emission factor of 5 kg CH 4 head proposed by the IPCC for small ruminants in the sub-Saharan Africa region, our suggested values are 56% and 60% lower for sheep and goat, respectively. These lower values took account of the particular flock structure of both sheep and goats. These estimates also accounted for differences in live weight according to age and corresponding estimated feed intake. This work is a step forward in the revision of small ruminant emission factors and can further support assessment of mitigation strategies in Senegalese livestock farming systems.