Estimation of enteric methane emissions in Sudanese Peul zebu cattle according to feeding strategies in West Africa

Résumé

Livestock in Sub-Saharan Africa (SSA) is attracting great attention not only because of its contribution to food security but also because of the greenhouse gas (GHG) emissions it causes. The GHG most emitted in livestock in this region is enteric methane (eCH4). This thesis project aims to do in vivo measurement of eCH4 emissions in Sudanese Fulani zebu based on the feeding practices of farmers in real environment. After a general introduction in this writing, Chapter 1 relates the different methods for measuring, predicting and mitigating eCH4 in tropical areas. Six (06) different measurement methods are reported to exist in the region. These are the GreenFeed system, the respiratory chamber, the sulfur hexafluoride, the methane laser detector. Not counting the three Tiers of IPCC, and GLEAM, twenty-seven (27) prediction classical models are reported in SSA to estimate this gas. For its mitigation, the nutritional and genetic strategies, the methanogenic immunization, and the system productions management are detailed in this chapter. The eCH4 emissions are linked to the quantity and quality of feed intake by ruminants, but in extensive systems, fodder is subject to seasonal variation along the rangeland. For this, emissions were measured in chapter 2 during the three main seasons of the year (wet, cold dry and hot dry seasons). The animals were fed rangeland fodder, taking into account the gradient in the quantity available on the rangeland in each season. Significant differences were reported in seasonal dry matter intake (DMI), apparent digestibility, and eCH4 emissions. The average emissions are 46.69±3.34 kg of eCH4/Tropical Livestock Unit per year. Variations of the different parameters measured in different zones and main seasons must therefore be taken into account in national inventories to refine eCH4 emissions in ruminants. The highest eCH4 yield is observed in the hot dry season, a period during which farmers supplement their animals with a diversity of local resources including crop co-products and tree legumes. The potential for mitigating eCH4 by these resources that farmers use was therefore the subject of study. In chapter 3, six co-products including four from cereals (maize, sorghum, rice, and millet straws) and two from legumes (cowpea and peanut haulms) were tested by supplementation at 25% with as a basic diet 100% forage. Diets containing the crop co-products showed high DMI but no differences were observed for digestibility. Cereal and legume co-products made it possible to mitigate emissions (g/kg DMI) by 23 and 20% respectively. Raising awareness among agropastoralists on the use of agricultural co-products is a perspective for mitigating eCH4 emissions in the Sahel. Tree legumes are concentrated in protein and are also potential resources for eCH4 reduction. Chapter 4 dealt supplementation with two tree legumes already included in the ruminants feeding in Africa. These are Gliricidia sepium and Leucaena leucocephala. A basic diet (100% forage) was also supplemented at 25% with each tree legumes. These resources significantly improved DMI and apparent digestibility. Emissions were mitigated by 32% and 42% for diets containing G. sepium and L. leucocephala respectively. The multiplication of fodder banks of these tree legumes is a crucial step to make these resources more available to livestock farmers in SSA. Furthermore, cultivated forages are now being popularized among ruminant farmers to improve animal feeding conditions. But the impact of the consumption of these forages in terms of eCH4 emissions remains little known in SSA. The objective of Chapter 5 is to compare the eCH4 emissions induced by three main cultivated grasses to those induced by rangeland fodder in the hot dry season. The cultivated forages are Andropogon gayanus, Brachiaria ruziziensis and Panicum maximum. The type of forage influenced the chemical component, intake and digestibility of the forages. However, the eCH4 emissions induced by these mature forages are no different from that caused by rangeland fodder. However, P. maximum may be preferred over other forages given its low eCH4 yield per unit of digestible matter intake. Measuring eCH4 emissions induced by these forages at different growth stages will make it possible to specify their optimum stage of use in a context of environmental sustainability. In the future, it would be interesting to carry out such work directly on rangeland in order to improve seasonal emissions, to test the other resources used by farmers to broaden the spectrum of potential resources for mitigating eCH4, and to popularize these results in a real environment.

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