This review aims to elucidate the contemporary methods of measuring and estimating methane (CH₄) emissions from ruminants. Six categories of methods for measuring and estimating CH₄ emissions from ruminants are discussed. The widely used methods in most CH₄ abatement experiments comprise the gold standard respiration chamber, in vitro incubation, and the sulfur hexafluoride (SF₆) techniques. In the spot sampling methods, the paper discusses the sniffer method, the GreenFeed system, the face mask method, and the portable accumulation chamber. The spot sampling relies on the measurement of short-term breath data adequately on spot. The mathematical modeling methods focus on predicting CH₄ emissions from ruminants without undertaking extensive and costly experiments. For instance, the Intergovernmental Panel on Climate Change (IPCC) provides default values for regional emission factors and other parameters using three levels of estimation (Tier 1, 2 and 3 levels), with Tier 1 and Tier 3 being the simplest and most complex methods, respectively. The laser technologies include the open-path laser technique and the laser CH₄ detector. They use the laser CH₄ detector and wireless sensor networks to measure CH₄ flux. The micrometeorological methods rely on measurements of meteorological data in line with CH₄ concentration. The last category of methods for measuring and estimating CH₄ emissions in this paper is the emerging technologies. They include the blood CH₄ concentration tracer, infrared thermography, intraruminal telemetry, the eddy covariance (EC) technique, carbon dioxide as a tracer gas, and polytunnel. The emerging technologies are essential for the future development of effective quantification of CH₄ emissions from ruminants. In general, adequate knowledge of CH₄ emission measurement methods is important for planning, implementing, interpreting, and comparing experimental results.

This study continued the in vitro screening of locally available ruminant feedstuffs for optimum nutrient composition and low methane (CH₄) production in Ethiopia. The best bet feeds from the in vitro study, hereafter called the test feeds, include dried leaves of Acacia nilotica, Ziziphus spina-christi, and brewery spent grains (BSG). The study involves four treatments: Control, Acacia, BSG, and Ziziphus; each treatment provided an equivalent crude protein and estimated enteric CH₄ emissions using Modeling and a Laser CH₄ detector (LMD). The experiment was designed as a randomized complete block, using initial weight as the blocking factor for 21 yearling castrated Menz sheep. The study spanned 90 days, and digestibility trials were carried out following a month of the feeding trial. The control group exhibited a significantly (p < 0.001) lower dry matter intake (DMI) compared to the test feed group, which had a higher intake, particularly in the Ziziphus group. However, the Ziziphus group demonstrated significantly (p < 0.01) lower CP digestibility than the other groups. The test diet also led to a significantly (p < 0.001) higher weight gain. Notably, the Ziziphus group demonstrated superior performance in weight change (BWC), final body weight (FBW), and average daily gain (ADG). Similar results were observed for CH₄ production (g/day), CH₄ yield (g/kg DMI), and CH₄ intensity (g CH₄/kg ADG) using both CH₄ measuring methods. The CH₄ emission intensity was significantly (p < 0.04) lower in the test feed groups than in the control group. The control group emitted 808.7 and 825.3 g of CH₄, while the Ziziphus group emitted 220 and 265.3 g of CH₄ per kg of ADG using the Modeling and LMD methods, respectively. This study indicates that LMD could yield biologically plausible data for sheep. Although the small sample size in the Ziziphus group was a limitation of this study, leaf meals from Ziziphus spina-christi and Acacia nilotica, which are rich in condensed tannins (CTs), have resulted in considerable weight gain and enhanced feed efficiency, thereby making these leaf meals a viable and sustainable feed option for ruminants in Ethiopia.

This research was conducted to evaluate the replacement potential of Acacia nilotica dried leaf meal for Noug Seed Cake (NSC) to supplement low quality grass hay in the diet of crossbred sheep (25% Dorper). In doing so, four treatments were set up in such a way that 0%, 33%, 67%, and 100% NSC is replaced with dried leaf of Acacia nilotica from a conventional supplement while the treatments were kept isonitrogenous. The experiment was set up in a Randomized Complete Block Design, with initials weight used as the blocking factor. Twenty animals were allocated to the four treatments. The experiment consisted of hundred days of feeding trial followed by evaluation of carcass components at the end. In addition, the experimental feed ingredient was studied in vitro for gas production, methane (CH₄) production, fractional rate of degradation (Kd), and in vitro dry matter digestibility (IVDMD). In view of chemical composition, grass hay contained lower crude protein (CP = 3.2% DM) and high cell wall contents that makes it lower quality feed. On the other hand, Acacia nilotica leaf meal was moderate in quality (CP = 14.3% DM) that can support moderate level of ruminant production. In an in vitro study, Acacia nilotica was found to have lower (P < 0.01) levels of CH₄, total gas, kd, and IVDMD compared to the other feed ingredients. This indicates that tannin have an effect on Acacia nilotica feed. Partial and complete replacement of NSC with Acacia nilotica leaf meal significantly increased total dry matter intake (TDMI) (P < 0.001). Average daily gain (ADG) and dressing percentage was also higher for leaf meal supplemented groups. Hot carcass weight was in the range of 14.8–17.8 kg, which is higher than the national average carcass weight for Ethiopian sheep, and it was also found to be higher when NSC was partially (33%) as well as completely replaced by the leaf meal. In general, NSC can be replaced either partially or completely with Acacia nilotica leaf meal in the diet of 25% Dorper crosses while weight gain as well as carcass yield is promoted. The maximum inclusion level of Acacia nilotica was 61.3% or 319.2 g per day for 25% Dorper cross sheep fed natural pasture hay as a basal diet.

This study was part of an in vivo investigation of methane (CH ₄ ) abatement feed on local Menz breed sheep in Ethiopia, conducted over 90 days period using a randomized complete block design. Sheep were subjected to four dietary treatments: Control, Acacia ( Acacia nilotica ), BSG (Brewer's Spent Grain), and Ziziphus ( Ziziphus spina-christi ). The aim of the study was to investigate the rumen microbial community composition, diversity, and their relationships with CH ₄ intensity. Rumen fluid was collected on days 0 (SD_0), 45 (SD_45), and 90 (SD_90), using an esophageal tube. The dynamics of the bacterial and archaeal domains were assessed by 16S rRNA gene sequencing. The sequencing results showed that 92.9% of ASVs were Bacteria, and 0.05% Archaea. At the genus level, Rikenellaceae RC9 gut group (18%), Prevotella (17%), and Candidatus Saccharimonas (8.9%) were the most abundant Bacteria, while Methanobrevibacter (88%) dominated the Archaeal genera across all treatment groups. Treatment feed significantly altered microbial profiles, notably reducing Methanobrevibacter abundance in CH ₄ abatement diets and increasing the presence of Methanosphaera . Shannon diversity increased in the abatement diet and decreased when the sheep were fed BSG. CH ₄ intensity was most strongly associated with the archaeal genus Methanomicrobium , but did not associate strongly with any other Bacteria or Archaea, although Methanobrevibacter and Methanosphaera were correlated negatively ( r = –0.97). CH ₄ intensity also did not covary with volatile fatty acids (VFAs), of which Acacia yielded the highest acetate (772 mmol/mol) and BSG the highest propionate (172 mmol/mol) concentration. The volatile fatty acids (VFAs) showed a strong correlation: a positive correlation between acetate and butyrate ( r = 0.80) and a strong negative correlation between acetate and propionate ( r = –0.92). These findings highlight the complex relationship between diet, rumen microbiota, and fermentation products, with implications for CH ₄ mitigation strategies in sheep.