Greenhouse gas (GHG) emission measurements from livestock excreta in Africa are limited. We measured CH 4 and N 2 O emissions from excreta of six Boran (Bos indicus) and six Friesian (Bos taurus) steers near Nairobi, Kenya. The steers were fed one of three diets (T1 [chaffed wheat straw], T2 [T1 + Calliandra calothyrsus Meissner -0.2% live weight per day], and T3 [T1 + calliandra -0.4% live weight every 2 d]). The T1 diet is similar in quality to typical diets in the region. Calliandra is a leguminous fodder tree promoted as a feed supplement. Fresh feces and urine were applied to grasslands and emissions measured using static chambers. Cumulative 28-d fecal emissions were 302 ± 52.4 and 95 ± 13.8 mg CH 4 -C kg -1 dry matter for Friesen and Boran steers, respectively, and 11.5 ± 4.26 and 24.7 ± 8.32 mg N 2 O-N kg -1 dry matter for Friesian and Boran steers, respectively. For urine from Friesian steers, the N 2 O emissions were 2.8 ± 0.64 mg N 2 O-N 100 mL urine In sub-Saharan Africa, livestock comprise a large proportion of total agricultural emissions, most of which is from enteric CH 4 production in ruminants (Valentini et al., 2014). However, between 7 and 15% of agricultural GHG emissions are associated with livestock manure (Smith et al., 2014;Tubiello et al., 2014). However, these emission rates from livestock manure in Africa are estimated using emission factors (EFs) from the International Panel on Climate Change (IPCC) that have been derived using measurements primarily from states within the Organization for Economic Cooperation and Development. These regions have livestock species, breeds, diets, management systems, and climatic conditions that often differ from those in tropical Africa (IPCC, 2006).In tropical and subtropical agricultural production systems, the climate is generally warmer than temperate systems, which could result in greater N 2 O and CH 4 emissions from excreta because emissions are often positively correlated with temperature (González-Avalos and Ruiz-Suárez, 2001;Rochette et al., 2014). However, the types of management systems used, the quality of the feeds, and the species of cattle raised may also affect emissions. The majority of African ruminants graze for much of their life (Schlecht et al., 2006), which results in over 40% of excreta Journal of Environmental Quality ATMOSPHERIC POLLUTANTS AND TRACE GASES TECHNICAL REPORTS Core Ideas• GHG emissions from African livestock excreta is lower than IPCC tier 1 emission factors.• Low-quality feeds with low protein content result in low N content of excreta.• Supplementation of cattle diet with calliandra reduced the methane emissions from cattle feces.• The species of cattle causes differences in GHG emissions from feces.

AbstractThe relationship between feed intake at production levels and enteric CH4 production in ruminants consuming forage-based diets is well described and considered to be strongly linear. Unlike temperate grazing systems, the intake of ruminants in rain-fed tropical systems is typically below maintenance requirements for part of the year (dry seasons). The relationship between CH4 production and feed intake in animals fed well below maintenance is unexplored, but changes in key digestive parameters in animals fed at low levels suggest that this relationship may be altered. We conducted a study using Boran yearling steers (n 12; live weight: 162·3 kg) in a 4 × 4 Latin square design to assess the effect of moderate to severe undernutrition on apparent digestibility, rumen turnover and enteric CH4 production of cattle consuming a tropical forage diet. We concluded that while production of CH4 decreased (1133·3–65·0 g CH4/d; P < 0·0001), over the range of feeding from about 1·0 to 0·4 maintenance energy requirement, both CH4 yield (29·0−31·2 g CH4/kg DM intake; P < 0·001) and CH4 conversion factor (Ym 9·1–10·1 MJ CH4/MJ gross energy intake; P < 0·01) increased as intake fell and postulate that this may be attributable to changes in nutrient partitioning. We suggest there is a case for revising emission factors of ruminants where there are seasonal nutritional deficits and both environmental and financial benefits for improved feeding of animals under nutritional stress.

Background: The Boran (Bos indicus), indigenous Zebu cattle breed from sub-Saharan Africa, is remarkably well adapted to harsh tropical environments. Due to financial constraints and low-quality forage, African livestock are rarely fed at 100% maintenance energy requirements (MER) and the effect of sub-optimal restricted feeding on the rumen microbiome of African Zebu cattle remains largely unexplored. We collected 24 rumen fluid samples from six Boran cattle fed at suboptimal and optimal MER levels and characterised their rumen microbial composition by performing shotgun metagenomics and de novo assembly of metagenome-assembled genomes (MAGs). These MAGs were used as reference database to investigate the effect of diet restriction on the composition and functional potential of the rumen microbiome of African cattle. Results: We report 1200 newly discovered MAGs from the rumen of Boran cattle. A total of 850 were dereplicated, and their uniqueness confirmed with pairwise comparisons (based on Mash distances) between African MAGs and other publicly available genomes from the rumen. A genome-centric investigation into sub-optimal diets highlighted a statistically significant effect on rumen microbial abundance profiles and a previously unobserved relationship between whole microbiome shifts in functional potential and taxon-level associations in metabolic pathways. Conclusions: This study is the first to identify 1200 high-quality African rumenspecific MAGs and provides further insight into the rumen function in harsh environments with food scarcity. The genomic information from the rumen microbiome of an indigenous African cattle breed sheds light on the microbiome contribution to rumen functionality and constitutes a vital resource in addressing food security in developing countries.

Given their high nitrogen (N) concentration and low costs, sweet potato vine silage (SPVS) and urea-molasses blocks (UMB) are recommended supplements for tropical regions; therefore, they were investigated in this study. Six heifers were allocated to three diets: the roughage diet (R) consisted of wheat straw (0.61) and Rhodes grass hay (0.39; on dry matter (DM) basis); R + SPVS combined R (0.81) and SPVS (0.19); and with R + UMB animals had access to UMB. During two experimental periods, feed intake, feces and urine excretion, digesta passage, and rumen microbial protein synthesis were determined during seven days and methane emissions during three days. There was no treatment effect (p > 0.05) on DM and N intake. Apparent DM digestibility of R + SPVS (510 g/kg) was higher (p < 0.05) than of R (474 g/kg). Digesta passage and duodenal microbial N flow were similar for all diets (p > 0.05), while N retention was highest with R + SPVS (p > 0.05). Methane emissions per unit of digested feed (g CH4/kg dDM) were lower (p < 0.05) for R + SPVS (55.2) than for R (64.7). Hence, SPVS supplementation to poor–quality roughage has the potential to increase diet digestibility and N retention while reducing CH4 emissions.