Enteric Methane Emissions Research Articles (Page 1)

Introduction The present study aimed to understand the shift in the rumen microbiome of buffaloes fed diets with and without phyto-additives. The rationale was based on the hypothesis that plant-based additives can modulate the microbial population in the rumen, potentially reducing methane production and enhancing fiber degradation. Given the possibility that prolonged use of the same additives may lead to microbial adaptation and diminished efficacy, the study also investigated the effects of periodically switching additives. Methods Three male buffalo calves were fed a control diet, while another three received additive-supplemented diets. Two additive formulations were used: FAI (a blend of garlic Allium sativum , ajwain Trachyspermum ammi , harad Terminalia chebula , and soapnut Sapindus mukorossi ) and FAII (ajwain oil). The additives were alternated every 15 days to prevent microbial adaptation. After 21 days of feeding, rumen liquor samples were collected 2 hours post-feeding for metagenomic analysis. The study included both in vivo and in vitro assessments of rumen fermentation. Results Metagenomic analysis revealed that dominant bacterial phyla included Prevotella, Bacteroides, Succiniclasticum, Fibrobacter, Clostridium, Alistipes, Ruminococcus , and Butyrivibrio , with over 50 bacterial species consistently present across all animals. The main archaeal phylum was Euryarchaeota (>85%), along with notable presence of Candidatus_Bathyarchaeota and Thaumarchaeota . At the genus level, Methanomicrobium and Methanobrevibacter each accounted for approximately 30% of the archaeal community, followed by Methanosphaera , Methanosarcina , and Methanomassiliicoccus . While total abundances of Archaea and Bacteroidota were not significantly different among groups, specific taxa within these phyla showed marked changes. Discussion The inclusion of phyto-additives in the buffalo diet influenced the rumen microbiome composition by reducing methanogen populations, particularly Methanobrevibacter , and enhancing fiber-degrading microbial communities. These microbial shifts were associated with improved fiber utilization and decreased methane emissions. Rotating the additives every 15 days appeared to sustain their efficacy over time, potentially by preventing microbial adaptation. This approach may offer a sustainable strategy to optimize rumen function and reduce enteric methane emissions in ruminants.

Effect of dietary starch concentration and direct-fed microbial supplementation on lactation performance, total-tract nutrient digestibility, and enteric methane emissions by dairy cows.

Increasing the proportion of grazed grass in the diet in early lactation and its impact on enteric methane emissions and rumen fermentation of pasture-based dairy cows

Does information matter? The effect of sustainability-related information on consumers' intentions to purchase beef.

Effect of plantain in perennial ryegrass-white clover pasture on the ingestive behaviour, rumen fermentation parameters, and enteric methane emissions of spring-calving dairy cows

The enteric methane (CH4) emission from dairy cattle is a significant factor contributing to anthropogenic climate change and the energy loss of animals. The objective of this study was to evaluate the prediction accuracy of the existing CH4 estimation models from dairy cattle, and to identify the most reliable model for quantifying CH4 emission. A database was compiled from 135 treatment means obtained from 81 peer-reviewed literatures, which included data on dietary composition, energy intake, and enteric CH4 emission from dairy cattle. Forty existing dairy cattle prediction models were evaluated using this dataset based on the root mean square prediction error (RMSPE), concordance correlation coefficient (CCC), the ratio of RMSPE to standard deviation (RSR), and error decomposition indicators (ECT, ER, and ED). Results indicated that the RSR of model 38 was the lowest (0.71) but there were large prediction errors. Considering all evaluation indicators, model 21, which included dry matter intake (DMI), demonstrated the most robust predictive performance (RSR = 0.83, RMSPE = 14.41%, ECT = 3.42%, ER = 0.74%, ED = 96.75%, CCC = 0.58). Therefore, it is recommended for estimating enteric CH4 emissions from dairy cattle. Future research will need to further improve the accuracy and robustness of enteric CH4 prediction models by establishing a more comprehensive large-scale database, and expand the applicability of the model in various dairy farming systems.

Methane emitted by ruminants represents an energy loss from feed intake and contributes to global warming. Fumaric acid (FA), a key intermediate in rumen metabolism, acts as an alternative electron acceptor and offers a potential strategy to reduce methane production. This meta-analysis systematically evaluated the effects of FA supplementation on enteric methane emissions and rumen fermentation in ruminants. Thirteen peer-reviewed studies met the inclusion criteria, contributing 22 effect sizes from 13 studies: six on cattle (dairy and beef cattle), seven on small ruminants (sheep and goats). Effect sizes were calculated as mean difference (MD) for methane yield (g/kg dry matter intake (DMI)), relative mean difference (RMD) for methane production (g/day) and DMI, (kg/day), and standardized mean difference (SMD) for volatile fatty acids. A multilevel meta-analysis model was used to account for study-level variation. Fumaric acid supplementation had no effect on DMI (P = 0.25; RMD = -2.75) but significantly reduced methane production (P = 0.005; RMD = -19.21). Meta-regression showed that increase in FA (g/kg DMI) decreases in methane production by 0.272% (P = 0.02). Methane production was significant in small ruminants (P = 0.002; RMD = -24.67) but not in cattle (P = 0.52; RMD = -7.03). The effectiveness of FA in reducing methane production was not (P > 0.05) affected by variations in dietary forage, concentrate, or neutral detergent fiber (NDF) content in FA-supplemented animals. Methane yield decreased (P = 0.001; MD = -1.954) in FA supplemented animals, while the efficacy of FA was not influenced (P > 0.05) by diet composition (forage %, concentrate %, NDF %). Fumaric acid had no effect on ruminal acetate (P = 0.49; SMD = -0.299), but increased propionate (P = 0.01; SMD = 0.970). In summary, FA supplementation did not affect DMI but reduced methane production and yield in small ruminants. While in cattle, FA supplementation may have limited impact on methane emission.

This study aimed to evaluate the effects of incorporating unqualified cacao pod powder into beef cattle diets on nutrient digestibility, rumen fermentation, greenhouse gas emissions, and blood metabolites. A 4 × 4 Latin square design was used with four of Brahman × Thai native crossbred steers (207.1 ± 45.1 kg BW). Treatments included; T1: a control (no supplement), T2: supplemented with 50 g/day of cacao powder, T3: supplemented with mineral block containing cacao powder and T4: both supplemented with 50 g/day of cacao powder and mineral block containing cacao powder. Results showed no significant effect on feed intake, but polyphenol and tannin intake increased (P < 0.01). Apparent digestibility of dry matter, organic matter, protein, and both detergent fiber increased with cacao supplementation (P < 0.01). Rumen pH, total volatile fatty acid, and acetate concentrations increased, while methane and carbon dioxide emissions were reduced (P < 0.01). Blood urea nitrogen levels decreased (P < 0.05), while concentration of white blood cell, red blood cell, hemoglobin and lymphocyte percentage remained unchanged. The neutrophil percentage tended to decrease, as same as, the neutrophil to lymphocyte ratio in the supplemented groups (P = 0.06 and P = 0.08, respectively). These findings suggest that unqualified cacao pods can enhance nutrient utilization and mitigate enteric methane emissions, offering a sustainable strategy for valorizing cacao byproducts in ruminant production.

The inhibition of methyl-coenzyme M reductase (MCR) effectively suppresses ruminal methanogen activity, thereby mitigating enteric methane emissions in ruminants. However, the development of highly specific and environmentally sustainable inhibitors remains a significant challenge. This study aimed to identify key bioactive compounds from Cannabis sativa L. residue (CSR) that function as novel methane inhibitors that specifically target MCR by computational molecular screening. Cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) were identified as potential candidate compounds using the molecular docking technique. CBD and THC were found to be compounds that can navigate through a narrow channel and bind to the active sites of MCR, with calculated binding free energies of -8.8 and -5.5 kcal/mol, respectively. Furthermore, the effects of CSR supplementation levels on rumen fermentation, nutrient digestibility, methane production, and the ruminal microbial population were investigated through in vitro rumen fermentation simulations, as well as in situ digestibility analysis according to a completed randomized design (CRD). Compared with the control, supplementation with 2% total DM substrate in a total mixed ration (TMR) diet resulted in a 34% decrease in methane production. In addition, CSR increased the molar proportion of propionic acid and the concentration of ammonia-nitrogen (NH3-N), whereas the molar proportion of acetic acid and the acetic acid to propionic acid ratio decreased. At the bacterial level, the population of R. flavefaciens decreased with CSR supplementation. At the archaeal level, the population of Methanobacteriales decreased with CSR supplementation. These findings suggest that CSR has the potential to be used as a novel natural additive for inhibiting ruminal methane production. Further in vivo studies are recommended to validate these findings. Supplementary InformationThe online version contains supplementary material available at 10.1186/s12917-025-04985-5.

This study examined dietary determinants of enteric methane (CH4) emissions in high-yielding Holstein Friesian dairy cows across different physiological stages. Emissions were estimated using the IPCC Tier 2 methodology during peak lactation, the full lactation cycle, and the dry period in two commercial groups with distinct productivity. Group A (38-40 kg milk/day) showed higher peak dry matter intake and fiber content than Group B (32-35 kg milk/day), which had greater ether extract (EE) levels. Peak-lactation CH4 emissions were significantly higher in Group A (P < 0.05), while dry-period values did not differ (P > 0.05). Dietary EE was inversely associated with CH4 output, suggesting a potential mitigation pathway. Phase-specific regression models (adjusted R2 = 0.88-0.93) confirmed diet composition and physiological stage as major drivers of emissions. Digital twin simulations based on these models offer a non-invasive, reproducible tool for predicting emission scenarios, which is particularly valuable in farms where direct measurements are impractical. These findings highlight the feasibility of integrating diet optimization and predictive modeling into herd management strategies, enabling substantial reductions in CH4 emissions while sustaining milk yield and overall productivity in intensive dairy systems.

Effects of 3-nitrooxypropanol on enteric methane emissions and milk production characteristics in dairy cows fed a high corn-silage diet in different environmental conditions.

Graduate Student Literature Review: Limitations in feeding red seaweed Asparagopsis species for enteric methane mitigation in ruminants.

Abstract Supplementation with non-protein nitrogen (NPN) has been used as an alternative to supply nitrogen in low-protein diets for ruminants. Urea is the primary source of NPN supplemented to cattle, but its rapid degradation rate in the rumen limits the inclusion level due to risks of ammonia toxicity. However, novel NPN formulations that include a mixture of urea and biuret (UB) result in lower degradation rates, which may allow for higher inclusion levels than urea alone. Thus, it was hypothesized that by using UB, the inclusion of NPN can be increased in beef cattle diets without impairing production efficiency or safety. The objective of this study was to evaluate urea supplementation at 1% and increasing inclusions of UB on beef steers performance and enteric methane (CH4) emissions. To this end, 128 Angus-crossbred steers were used in a generalized randomized block design. Treatments were composed of a corn-silage basal diet supplemented with urea at 1% of the diet dry matter (DM) (U1), or supplemented with UB at 1.12% (UB1), 2.24% (UB2), or 4.48% (UB4) of the diet DM. The experimental period consisted of 24 d of adaptation, followed by 86 d of performance data collection, and 5 d of enteric CH4 emissions measurements using the sulfur hexafluoride tracer technique. No differences in dry matter intake were observed among treatments (P = 0.41). The UB4 treatment decrease average daily gain (ADG) when compared with U1 (P = 0.05), while no differences were observed among U1, UB1 and UB2. Similarly, gain to feed ratio decreased for the UB4 treatment when compared with U (P = 0.005), though no differences were observed among U1, UB1 and UB2. Total CH4 emission rate (g/d) and CH4 intensity (g/kg ADG), were not affected by treatments (P &amp;gt; 0.05). In conclusion, UB supported equivalent performance to U, when included at 1.12% or 2.24% of the diet DM without compromising efficiency or increasing CH4 emissions. However, the highest inclusion level (4.48%) impaired feed efficiency. These results demonstrate that UB formulation allows NPN supplementation at higher dietary inclusion levels than conventional urea, thereby expanding the safety margin of NPN utilization in beef cattle diets.

Abstract Maternal gut microbiome has been shown to influence immune, metabolic and neurodevelopmental programming of offspring from the embryonic stage, suggesting a potential role in the Developmental Origins of Health and Disease (DOHaD). Whereas many still support the “sterile-womb hypothesis” that the neonatal microbiome acquisition occurs only during and after birth, very recent studies have provided evidence showing the existence of in utero microbial colonization. Thus, these recent developments in the field of microbiome research of human and vertebrate animals including bovine animals highlight that the maternal gut microbiome during pregnancy should be targeted for harnessing their extended impact on the offspring’s development and health. In this presentation, we will discuss the potential involvement of maternal microbiome and feto-maternal microbial crosstalk in fetal programming, and offspring calf’s health and development. In addition, we will discuss the results from our recently conducted longitudinal study focused on the evaluation of the impact of altering maternal microbiota via high forage or high concentrate diets on offspring microbiome development, energy balance, methane emissions and feedlot performance in beef cattle. For this, 120 beef heifers were assigned to one of two treatments and received a diet based on 75% forage (HF) or 75% concentrate (HC) from 15 days pre-breeding through calving. Heifers were bred using male-sexed semen and fed to target a gain of 0.45kg/d for both groups. Ruminal fluid, fecal and vaginal swabs were collected from both HF (n = 24) and HC (n =22) heifers on pre-breeding (-30, -2), post-breeding (56, 91, 180, and 238 days of gestation) and at calving. Calves born from these heifers were monitored for their animal performance, feed efficiency, gut microbiome development and enteric methane emission (in vitro and in vivo). Body weight measurements, ruminal fluid and fecal samples were collected from the calves at 0, 15, 30, 60, 120, 160, 240, 330 and 340 days old. The 16S rNRA gene sequencing was performed on the dam and calf’s microbiome samples. An in-vitro fermentation assay was performed on the ruminal fluid samples from heifers and their calves for methane and VFA analyses. During finishing stage, a subset of calves born from HF and HC dams (n = 10 each group) were evaluated to examine effects on energy metabolism, nutrient balance and enteric methane emission (using headbox) output between the HF and HC offspring because of the HF or HC diet their dams received during fetal development. The results from this study provide novel insights into the impact of altered maternal gut microbiome during pregnancy on the postnatal animal performance, feed efficiency, microbiome development and enteric methane emission phenotype in cattle.

Abstract Rising global temperatures have intensified the urgency to reduce greenhouse gas (GHG) emissions from anthropogenic sources, including agricultural methane (CH4). CH4 is a potent GHG produced as a byproduct of ruminal fermentation in cattle. CH4 warms the atmosphere 28 times more than carbon dioxide (CO₂) over a 100-year period, making it a critical GHG mitigation target. Multiple approaches are being developed, but the beef cattle industry lacks solutions that effectively reach ~80% of bovine CH4 emissions produced in extensive, pasture-based systems, e.g., the cow-calf and stocker segments. One promising approach is a methane-reducing vaccine. Methane-reducing vaccines stimulate the production of anti-methanogen antibodies. These antibodies potentially enter the rumen, bind to their methanogen targets, and inhibit ruminal methanogenesis, thereby reducing enteric CH4 emissions. The objective of this trial was to assess the effect of a proto-type vaccine on growth performances, gas flux, and feeding behavior in beef cattle. Thirty Angus crossbred steers (n = 30; 451 ± 11 kg) were blocked by body weight (BW) and stratified by breed before being randomly assigned to one of two treatments: control (n = 20) or vaccine-treated (n = 10). Animals received a prime-boost vaccine regimen (2 mL, each) administered subcutaneously on days 0 and 21. Animals were housed in three pens, each equipped with three electronic feed bunks (Vytelle, Lenexa, KS) for recording individual feed intake and feeding behavior, as well as one GreenFeed emission monitoring system (C-lock Inc., Rapid City, SD) for measuring CH4 emissions. Weekly BW, daily feed intake, and gas emissions were measured over an 84-day period. Statistical analyses were conducted in JMP Pro v.16 (SAS Institute Inc., Cary, NC), with individual animals as the experimental unit, and treatment as a fixed effect. There were no significant differences in average daily gain (ADG), initial BW, mid-test metabolic BW (BW⁰·⁷⁵), DMI, alfalfa pellet intake or gain: feed (P &amp;gt; 0.05). The vaccine-treated group had 15% lower (P = 0.0050) CH4 production (g/d), 18% lower (P = 0.0038), CH4 intensity (g/kg BW 0.75) and 13% lower (P = 0.0149) CH4 yield emissions (g/kg DMI) compared to the control. However, CO2 production (g/d), CO2 yield (g/kg DMI) and H2 production (g/d) did not differ (P &amp;gt; 0.05). Bunk visit (BV) duration was also similar between groups (P &amp;gt; 0.05). However, the vaccine-treated group had fewer BV per day (P = 0.0292) and a longer BV head-down duration per day (P = 0.0105), with a tendency for a slower eating rate (P = 0.0697) compared to control. These results highlight the potential of vaccination as a strategy to mitigate enteric CH4 production in beef cattle without negatively impacting growth performance.

Abstract The objective of this study was to obtain (co)variance components, heritability, and genetic and phenotypic correlation estimates for enteric methane emission, residual feed intake, growth and carcass trait and reproductive indicators. Data from 146 feed efficiency trials with male and female Nellore cattle born between 2008 and 2023 from 146 herds in Central Brazil were analyzed. Trial data along with diet NDF content were used to estimate the methane emission intensity (g CH4/kg ADG) for each individual, using an equation developed by Medeiros et al., 2014: CH4 (g/d) = -0.1011 + 0.02062*DMI (kg/d) + 0.001648*NDF (% of DMI). Other data included pedigree information, body weight, carcass traits and reproductive indicator traits. Numbers of records varied from 3,869 (methane) to 42,840 (carcass data). Continuous traits were analyzed using a linear animal model. Two-trait analyses were performed using the restricted maximum likelihood to estimate the variance components, heritabilities and genetic and phenotypic correlations among traits. The estimated heritability of methane emissions was 0.117 ± 0.025. The genetic correlations of methane emissions with most performance and reproductive traits were low and not different from zero: BW at 240 d (0.019 ± 0.0003), BW at 450 d (0.022 ± 0.0003), ribeye area (-0.077 ± 0.098), rib fat (-0.020 ± 0.094), rump fat (0.091 ± 0.089), intramuscular fat % (-0.008 ±0.109), scrotal circumference (0.015 ± 0.0004), and age at first calving (0,072 ± 0,187), The same was true for early calving probability (-0,139; -0,384, 0,106) and stayability (-0,079; -0,324, 0,166) (means and highest posterior density intervals). Exceptions were the moderate genetic correlations of methane emissions with DM intake (0.486 ± 0.018) and the high correlation of methane with residual feed intake (RFI; 0.808 ±0.015). Thus, selection to improve weaning and yearling weights and carcass traits would not affect methane emissions. Genetic selection to reduce methane emissions is feasible and would also reduce DMI and RFI. Conversely, selection to improve RFI can be used to identify animals with lower methane emissions. Medeiros, S. R, L. G. Barioni, A. Berndt, M. C. Freua, T. Z. Albertini, C. Costa Jr., and G. B. Feltrin (2014) Modeling enteric methane emission from beef cattle in Brazil: A proposed equation performed by principal component analyses and mixed modeling multiple regression. Anais, Livestock, Climate Change and Food Security Conference, Madrid.

Abstract Methane (CH4) emissions in ruminant systems are a loss of energy intake and a major contributor to climate change. This study evaluated the effects of increasing levels of non-protein nitrogen (NPN; 0.75, 1.5, and 3.0% dry matter basis) on enteric methane emissions and growth performance in finishing diets fed to beef steers. One hundred and eighty steers (IBW= 455 ± 41.5 kg) from 4 different sources were stratified by body weight (BW) and source and then randomly assigned to 1 of 4 NPN treatments. Steers were housed at Colorado State University’s Climate-Smart Research Facility. Daily gas flux and dry matter intake (DMI) were individually determined using SmartFeed and GreenFeed technologies (Rapid City, SD). Steers were acclimated for 35 days before a 13-day covariate period, where baseline CH4 emissions and feed intake data were collected. During the covariate period, a common finishing ration was fed (1.5% NPN treatment). Then, steers were fed their respective treatment for 53 days, and intake and methane emissions were measured continuously. Animal body weights were collected two consecutive days prior to beginning the NPN treatment and at the end of the experiment. Data were analyzed using R statistical software (4.4.3) and JMP (18.1.2), where NPN level, source, the interaction of source and NPN level, and covariate emissions and DMI were included in the model. Significance was declared at P &amp;lt; 0.05. Methane emissions were not different (P = 0.26) among treatments. However, CH4 yield (g/kg DMI) was greater (P &amp;lt; 0.05) for steers supplemented with 1.5% of NPN. Methane intensity (g/kg ADG) was greater (P&amp;lt; 0.05) for steers supplemented with 1.5% NPN treatment compared to those supplemented with 3.0% NPN. Steers supplemented with 0 and 0.75% of NPN had greater (P &amp;lt; 0.05) DMI than those supplemented with 1.5% NPN. Steers supplemented with 3.0% of NPN (P &amp;lt; 0.05) had intermediate DMI. Average daily gain (kg/d) was not different (P = 0.40) among treatments. Steers supplemented with 1.5% of NPN had a greater (P &amp;lt; 0.05) gain-to-feed ratio (G:F). In conclusion, increasing NPN levels in finishing diets can affect DMI, G:F, methane yield, and methane intensity without affecting ADG or enteric methane production.

Abstract This study pursued two objectives: (1) to verify the detectability of cattle burp acoustic patterns and their utility for robust classification, and (2) to develop an automated detection pipeline from long-term recordings for large-scale burp monitoring in real-world conditions. Enteric methane emissions account for an estimated 30–32% of global methane output and approximately 72% of total livestock-related greenhouse gas emissions, making them a critical environmental concern. Among these enteric emissions, ruminant burps generate 87–93%, underscoring the feasibility and impact of automating burp detection to mitigate greenhouse gases in livestock systems. A total of 6,810 hours of audio were recorded from 30 beef cattle under an open rotational grazing system, of which 100 hours were examined in detail to identify 301 expert-confirmed 5-second burp clips and 602 non-burp clips. Based on Mel-spectrogram analyses, we proposed two key preprocessing strategies—low-pass filtering (1,024 Hz) and upsampling (16 kHz)—and systematically tested them under four configurations. The Audio Spectrogram Transformer (AST) was trained using a 10-fold Monte Carlo Cross-Validation, yielding accuracy, mean average precision (mAP), burp precision, burp recall, and burp F1-score; Two-way ANOVA was conducted to assess the effectiveness of each preprocessing approach. Subsequently, an ensemble model was built from the best AST checkpoints across folds, employing a sliding-window approach (5-second window, 0.5-second step) with probability averaging and an optimized detection threshold from validation and test sets. Two-way ANOVA revealed that both low-pass filtering and upsampling significantly improved accuracy and burp F1-score (p &amp;lt; 0.05), with only upsampling being significant for burp recall, and no significant differences observed for mAP and burp precision. Under the best-performing setup—combining filtering and upsampling—accuracy reached 0.919 ± 0.0218, mAP 0.952 ± 0.0186, burp precision 0.935±0.0406, burp recall 0.818 ± 0.0605 and F1-score: 0.871 ± 0.0401. When tested on 10 hours of new audio (five cows, day/night), the ensemble-based pipeline delivered a burp recall of 0.821, precision 0.867, and an F1-score of 0.844, confirming strong generalization in different ambient conditions. In conclusion, this low-cost audio-based approach provides a scalable, non-invasive tool for continuous monitoring of enteric methane emissions. By accurately identifying burp events—responsible for the majority of methane release in ruminants, the proposed method holds promise for large-scale adoption in Precision Livestock Farming, ultimately contributing to more effective greenhouse gas mitigation strategies in the livestock industry.

Abstract This study aimed to evaluate the effects of low dosages of tannin-based product tannin supplementation on the performance, methane emissions, and rumen microbiome of Nellore cattle in a feedlot system. A total of 98 uncastrated male Nellore cattle were randomly assigned to four treatments: 1) CON: Negative control (basal diet without feed additives); 2) TAN08: Basal diet + 0.8 g/kg of DM of a tannin-based product; 3) TAN16: Basal diet + 0.16 g/kg of DM of tannin-based; and 4)TAN32: Basal diet + 0.32 g/kg of DM of tannin-based product. The tannin-based product was composed of quebracho, and chestnut tannin extracts along with carriers from cereals rich in saponins; SilvaFeed BX, Silvafeed®. The diet consisted of 82% concentrate and 18% forage (DM basis). Animals were housed in four collective pens, each equipped with four automated Intergado® feeders to record individual feed and water intake. Animals were weighed after 12 hours of fasting on the beginning (d0) and last d of the experiment (d 133). Data was analyzed as a completely randomized design by fitting a generalized linear mixed model (GLIMMIX procedure) and considering treatment as a fixed factor, and animal as random. Continuous outcome variables were by using least square difference test and polynomial linear regressions for additive levels. Animal performance results indicated that DMI linearly increased with tannin supplementation, particularly in the TAN32 group (P = 0.02). Average daily gain (ADG) quadratically increased with TAN16 presenting the highest value (P = 0.04), 1.203 g/d vs. 1.053 g/d, for TAN16 and CON, respectively. Despite not difference observed in hot carcass weight this increase and ADG for TAN16 compared to control resulted in 3.6% increase in hot carcass weight for TAN16 compared to CON. Methane emissions were significantly reduced in the TAN32 group compared to the control diet (P = 0.02), with a linear reduction in CH4 total emissions (g/d), intensity (CH4/HCW), and in CH4 emissions per unit of dry matter intake (CH4/DMI, P &amp;lt; 0.05), demonstrating the potential of tannins to mitigate enteric methane emissions up to 20% when compared to CON. Rumen microbiota analysis revealed shifts in bacterial composition, with a reduction in the genus CF231 (Paraprevotellaceae) and an increase in Roseburia in TAN16 and TAN32. Furthermore, a significant linear reduction on the relative abundance of methanobrevibacter with the increasing levels of TAN. In conclusion, tannin supplementation in Nellore cattle finishing diets increased ADG, leading to a slight increase in HCW. Notably, tannins significantly reduce methane emissions, especially at 16 and 32 g/animal/d, and alter the rumen microbiota, reducing methanogenic archaea like Methanobrevibacter. These results suggest tannins can enhance environmental sustainability in beef cattle production.

Abstract Cattle are the largest emitters of greenhouse gases (GHG), specifically methane (CH4), due to their ruminant digestive system. Cows are unable to directly digest the complex carbohydrates in the plant tissues they consume. Instead, they rely on enteric fermentation from microorganisms in the rumen to break down these tissues. During this process, hydrogen and carbon dioxide in the rumen are converted into CH4, which is expelled through eructation. Methane production is energetically inefficient to the animal, with cattle typically losing 6% of their ingested energy as enteric CH4. Research on enteric CH4 emissions of grazing cattle is limited, therefore deserving more exploration. The goal of our study was to characterize the seasonal variation in enteric CH4 emissions of beef cows grazing native sagebrush steppe. The study began in spring of 2024 with twenty-two cows (Angus × Hereford, 545 ± 17 kg) from the Eastern Oregon Agricultural Research Center (EOARC; Burns, Oregon). Methane emissions (g/day) were measured using the Greenfeed Pasture System monitoring units (C-Lock). Prior to the grazing season, all cows were acclimated the monitoring units. During the acclimation period, they were maintained as a group and provided meadow hay ad libitum. Fifteen cows were successfully acclimated. After the acclimation period, cows and monitoring units were relocated to the Northern Great Basin Experimental Range (NGBER; Riley, Oregon) for the measurement of enteric CH4 emissions during the grazing season over summer and fall. The monitoring units were placed near water sources and programmed to record up to 8 visits per cow each day, with alfalfa pellets used as an enticement. Cows were fitted with virtual fence collars (Vence) to assist with grazing management and composite forage samples were collected for forage nutrient analyses. Preliminary data for CH4 emissions during spring, summer and fall were analyzed as repeated measures with the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC, USA). Statistical significance was defined at P ≤ 0.05. Spring, summer, and fall forage CP and TDN were 8.5% and 56%, 3.5% and 57%, and 2.8 % and 55%, respectively. Approximately 9,000 CH4 emission readings were collected from spring through fall. Methane emissions were greatest (P &amp;lt; 0.0001) during summer (213 ± 1.06 g/cow daily), and similar between spring and fall (198 ± 1.40 g/cow daily; P = 0.51), illustrating the seasonal variation in emissions of grazing beef cattle.