Livestock sustainability research in Africa with a focus on the environment

Livestock in African countries contribute to about 10% of enteric methane emissions from dairy cattle worldwide despite producing only 3.9% of the world’s milk. Livestock in Sub-Saharan Africa also cause extensive land degradation with 48% of rangelands in SSA degraded due to overgrazing. Strategies for sustainable intensification of livestock such as improving quality of feed, range and grazing land rehabilitation, introduction of improved forages and silvopastoral systems, and improvement of herd genetics can reduce both total emission and emission intensity while improving productivity. Sustainable intensification strategies are not always readily adopted, therefore, smallholder farmers in Africa require policy directives, financial and technical support. Africa’s livestock accounts for one-third of the global livestock population (AU-IBAR, 2016) and about 40% of agricultural GDP in Africa, ranging from 10% to 80% in individual countries (Panel, 2020). Livestock will be increasingly important in the future in sub-Saharan Africa (SSA) because the demand for animal-source food (ASF) is projected to increase due to population growth, increased incomes, and urbanization. By 2050, consumers in low- and middle-income countries will demand 107 million tons more meat and 5.5 million tons more milk than they did in 2005/2007 (Alexandratos and Bruinsma, 2012). The current per capita annual consumption of meat and milk of about 14 kg and 30 L, are projected to rise to 26 kg and 64 L, respectively, by 2050 in SSA (AU-IBAR, 2016). However, African livestock also have significant impacts on the environment (Gerber et al., 2013). More than 70% of agricultural GHG emission in Africa comes from the livestock sector dominated by enteric methane (CH4) emission (Tubiello et al., 2014). Greenhouse gas emission intensity (i.e., emissions per unit of livestock product) in east Africa is four times greater than the global average (Pressman et al., 2018), and estimates from other parts of SSA are likely similarly high. The North American average milk yield of 9,000 kg/cow per year is much greater whereas the carbon footprint of 1.3 kg of CO2-eq./kg of milk is much lower than the corresponding SSA estimates of 250 kg/cow per year and 7.6 kg of CO2-eq./kg of milk, respectively (Capper, 2011). Livestock production in SSA causes extensive land degradation, overgrazing, and associated loss of biodiversity. For instance, UNEP (1992) reported that 58% of all land degradation and soil erosion in SSA is caused by overgrazing. This is because as the human population increases, more and more pastureland is used for food crop cultivation, increasing stocking rate, and grazing pressure on remaining grazing lands. A study in central Ethiopian highlands (Mekuria et al., 2018) showed that cropland increased by 16% while grazing lands decreased by 52% from 1984 to 2016. Free grazing livestock also hamper soil and water conservation in degraded areas (Giday et al., 2018). If agricultural knowledge, science, and technology do not improve, a general decline in species abundance in Africa due to livestock grazing is predicted at least until 2030 (Alkemade et al., 2013). Livestock grazing also causes encroachment on rangelands of grazing-resistant and unpalatable bushes, severely reducing rangeland plant biodiversity (O’Connor et al., 2014). This review examines the state of knowledge, policies, and practices on sustainability of livestock production in Africa and changes needed to drive improvements. In Africa, sustainable livestock production must address food security and climate change concerns simultaneously in addition to social and economic aspects. The need for and principles of sustainable livestock production apply universally. Although many high-income countries focus on the environmental impacts of livestock production, low-income countries are concerned with increasing livestock productivity to improve income and food supply and reduce high rates of childhood undernutrition and stunting (Tricarico et al., 2020). Currently, most countries in Africa rely on the Intergovernmental Panel on Climate Change (IPCC) tier 1 methodology to estimate their livestock-based emissions. However, detailed, and precise activity data are lacking, and accurate estimates of natural resource use and environmental impact by livestock in Africa, particularly SSA are scarce. Global greenhouse gas emissions from livestock were estimated at 7.1 Gt CO2-eq./annum in 2013, which is 14.5% of human-induced GHG emissions (Gerber et al., 2013). Enteric fermentation from ruminants is only second to feed production in its contribution to overall GHG emissions from livestock. Gerber et al. (2013) reported that ruminants in SSA contribute a large share of global GHG emissions due to their high emission intensity. This is because of the low productivity levels of African livestock. For instance, the mean milk production in Africa ranged from 108 to 3,368 kg/cow per year (IPCC, 2019), with about half of the countries producing below 500 kg milk/cow per year (FAOSTAT, 2018). Consequently, African countries contribute to about 10% of enteric CH4 emissions from dairy cattle worldwide despite producing only 3.9% of the world’s milk (FAOSTAT, 2018). Therefore, the intensity of CH4 emissions (g/kg milk) is much larger in Africa compared to the rest of the world. For comparison, in the United States, the average CH4 intensity is about 13 g CH4/kg milk. Figure 1 shows an analysis of the FAOSTAT (2018) database indicating that most African countries had intensity values of 50 to 100 g CH4/kg milk with nine countries over 300 g CH4/kg milk. A histogram showing the number of African countries that have a CH4 intensity (g CH4/kg milk) factor within each class (based on FAOSTAT (2018) database). A histogram showing the number of African countries that have a CH4 intensity (g CH4/kg milk) factor within each class (based on FAOSTAT (2018) database). Regional analysis of CH4 intensity in Africa showed that the systems with the lowest values (most efficient) were in Northern Africa (mean = 46 ± 12 g CH4/kg milk). In these countries, the dairy production system relies mainly on irrigated forages and uses either high genetic merit or crossbred cows (Sraïri et al., 2013). Northern African farmers use off-farm high-quality purchased feed resources which may represent up to 60% of the total energy intake (Kadi and Djellal, 2009). However, water is a major constraint to increasing forage production in this region. Sustainability of farms in the region relies on technologies that improve water use efficiency for feed production (Sraïri et al., 2013). Southern Africa had the second lowest CH4 intensity (mean = 102 g CH4/kg milk: SD = 56 g CH4/kg milk). The CH4 intensity range in this region is greater compared to Northern Africa covering 25.5 (South Africa) to 226 g CH4/kg milk (Madagascar) partly because many of their dairy farms have more than 500 cows and use a total mixed ration (TMR) feeding system leading to annual milk production of over 3,000 kg/cow (Dolecheck and Bewley, 2018). Whereas, in countries such as Madagascar and Zimbabwe, annual milk production is <500 kg/cow leading to much greater CH4 intensity. Western Africa had the third lowest CH4 intensity ranging from 54.3 g CH4/kg milk in the Republic of Congo to 610 g CH4/kg milk in Côte d’Ivoire (mean = 194 g CH4/kg milk; SD = 176 g CH4/kg milk). The wide range in CH4 intensity in the region reflects the various production systems and efficiency of milk production. About 50% of milk in Western Africa is produced by nomadic herders and agro-pastoralists (Seyoum, 1988) that use local breeds with low-quality feeds, causing greater CH4 intensity. The greatest CH4 intensity was in Eastern Africa with an average of 233 g CH4/kg milk, but the intraregional variation was smaller compared to Western Africa (SD=110 g CH4/kg milk). This region is characterized by mainly smallholder farmers, who experience various challenges including problems with overgrazing, a lack of infrastructure (very few milk collection locations and product manufacturers), little access to credit, and difficulty transferring technical knowledge and skills to farmers (Dolecheck and Bewley, 2021). The CH4 intensity of beef production in Africa is also high, particularly in SSA. The enteric CH4 emissions values were based on IPCC (2019) tier 1 calculations because of lack of research that directly measures emissions. A recent study using respiration chambers showed that that tier 1 emission factors from IPCC overestimated both CH4 and nitrous oxide emissions from cattle excreta in Kenya, given typical smallholder practices in Eastern Africa (Pelster et al., 2016). The Feed the Future Innovation Lab for Livestock Systems is addressing this problem by installing state-of-the-art CH4 measurement devices (GreenFeed, C-Lock Inc., Rapid City, SD) for large and small ruminants in East and West Africa, respectively, to quantitatively measure CH4 emissions from tropical cattle. Data from this type of research will lead to better quantification and development of the tier 2 system that takes into account factors that affect emissions such as diet quality and feed intake. Most ruminant feeds in Africa are low-quality crop residues and natural pasture making up 72% to 93% of total feed consumed by livestock (FAO, 2014). Improving crop residue entails increasing the crude protein concentration and/or digestibility using physical, biological, or chemical treatment of crop residues, thus potentially increasing intake and digestibility and reducing enteric CH4 emission intensity. This approach is also more feasible than concentrate supplementation due to the lower cost. Ammonization and alkali treatment of roughages reduces methane intensity (i.e., decrease methane produced/unit of output) by increasing animal productivity. However, urea treatment is more commonly used than alternatives and has the greatest uptake potential when the costs, hazards, and efficacy of chemical treatments are considered (Woyengo et al., 2004). Using urea-treated crop residues in ruminant diets was compared with traditional diets (untreated straw) and resulted in reduced GHG emissions by 1.02 Mt CO2-eq. annually (5.5%) in Ethiopia and 3.18 Mt CO2-eq. annually (8.8%) in Kenya (Pressman et al., 2018). The adoption of crop residue improvement technologies in Africa, however, is limited by the lack of technologies that fit the social, economic, and ecological conditions. Research is, therefore, required to develop technologies that are fit to smallholder production systems (Owen et al., 2012). Physical crop residue treatment techniques such as grinding, chaffing, and chopping of roughage or fibrous feeds also have reduced enteric CH4 emission by about 10% through improvement of feed intake, digestibility, and improved microbial activity or fermentation as a result of increased surface area of the substrate (Valli, 2020). Similarly, pelleting reduces feed waste by up to 5%, thus reducing emissions, while reduction in particle size from 1,000 to 600 microns increases dry matter and nitrogen digestibility by 5% to 12% and reduce nitrogen in manure by 20% to 24% (Carter et al., 2012). Quality of crop residues can also be improved through crop breeding particularly when aimed at improving the digestibility of dual-purpose crops. Crop residues or other fibrous feeds differ in their digestibility and, therefore, enteric methane emission (Giger-Reverdin and Sauvant, 2000). A cultivar-dependent difference in matter digestibility of about which is considered high in of its impact on animal productivity and enteric methane emission has et al., 2020). Crop breeding for improving quality of crop residues a potential for improving quality of animal and reducing emission intensity. However, is important to that crop breeding for improvement of crop residue quality simultaneously increases or at least not decrease such will not with African smallholder farmers who food than feed production et al., 2020). strategies for improving ration supplementation with and the use of to improve feed use efficiency and reduce enteric CH4 emissions. In most production systems in Africa, are is to their due to the feed quality and animal et al., 2020). the ration in dairy cows has reported to reduce emission intensity of milk by and energy loss through CH4 by et al., 2013). protein reduces nitrogen reducing emissions through crude protein in beef cattle diets from to reduced nitrogen emissions by and 2009). However, reduction of protein for dairy cattle must be to milk production. use of technology may require and accurate quantification of the of local The most commonly used has from using Western breeds such as the et al., However, SSA cattle are which have than breeds for at Therefore, is a need for development of systems for local and The low livestock productivity in SSA is due to the of This can be by and energy through or low-quality feed with that are greater in In crop residues with such as and reduced enteric CH4 production by et al., A of 20% roughage resulted in a mean decrease in enteric CH4 emissions in production systems in Ethiopia et al., 2020). However, the reduction in CH4 emissions due to concentrate supplementation may be by increases in other such as land and when more are and et al., 2012). The with supplementation is the high of energy or due to or for use in human and production of such is needed to reduce production and by smallholder livestock and strategies are to improve livestock systems, while climate change and environmental et al., 2016). of various of the livestock system can reduce GHG emissions and emission both enteric and from and increase carbon to a carbon et al., feed production systems, such as silvopastoral and other systems, can contribute to a reduction in GHG emissions from livestock through improved feed quality and contribution to carbon et al., 2018). 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