Ruminal methane production: Associated microorganisms and the potential of applying hydrogen-utilizing bacteria for mitigation

The role of monoammonium glycyrrhizinate as a methane inhibitor to limit the rumen methane emissions of Karakul sheep

Methane (CH4) from ruminant production systems produces greenhouse gases that contribute to global warming. Our goal was to determine whether monoammonium glycyrrhizinate could inhibit CH4 emissions over the long term without affecting animal performance and immune indices in Karakul sheep. This study aimed to assess the effects of medium-term (60 days) addition of monoammonium glycyrrhizinate on growth performance, apparent digestibility, CH4 emissions, methanogens, fibre-degrading bacteria and blood characteristics in Karakul sheep. Twelve male Karakul sheep (40.1 ± 3.59 kg) with fistula were randomly divided into two groups (n = 6): the Control group received a basal diet + the same volume of distilled water (30 ml) and the Treatment group received a basal diet + 8.75 g/kg monoammonium glycyrrhizinate injected via fistula. The adaptation stage was 15 days, and the measurement stage was 60 days. The sampling during the measurement stage was divided into two stages, stage I (1 ∼ 30 d) and stage II (31 ∼ 60 d). The results showed that monoammonium glycyrrhizinate significantly reduced the relative abundance of Bacteroides caccae, daily CH4 emission and protozoa population, significantly increased the relative abundance of Lachnospiraceae bacterium AD3010, Lachnospiraceae bacterium FE2018, Lachnospiraceae bacterium NK3A20, Lachnospiraceae bacterium NK4A179 and Lachnospiraceae bacterium V9D3004 in stage I (P < 0.05); significantly increased the relative abundance of Lachnospiraceae bacterium AD3010, but significantly decreased the relative abundance of Lachnospiraceae bacterium NK4A179 and Lachnospiraceae bacterium C6A11 in stage II (P < 0.05). Therefore, monoammonium glycyrrhizinate could be used as a CH4 inhibitor to limit the rumen CH4 emissions of Karakul sheep in short-term period (30 days) without affecting the growth performance, fibre digestibility and blood parameters.

Heat-Killed Lactobacillus acidophilus Promotes Growth by Modulating the Gut Microbiota Composition and Fecal Metabolites of Piglets

Probiotics can improve animal growth performance and intestinal health. However, understanding the effects of paraprobiotics on the growth performance and gut microbiota of piglets and how the paraprobiotics exert their impact are still limited. The present study was conducted to investigate the effects of heat-killed Lactobacillus acidophilus IFFI 6005 supplementation on the growth performance, intestinal microbiota, and fecal metabolites of piglets. First, a feed-additive sample of heat-killed Lactobacillus acidophilus IFFI 6005 was prepared by culture. Second, 96 (initial BW = 14.38 ± 0.67 kg, weaning age of 40 days) healthy piglets were selected and randomized into four treatment groups. Each treatment group consisted of three replicates (n = 8). Pigs were fed a basal diet (NC), basal diet plus antibiotics (PC), basal diet plus Lactobacillus acidophilus IFFI 6005 at 600 g/t (LA, 1.0 × 1010 cfu/g), and basal diet plus heat-killed Lactobacillus acidophilus IFFI 6005 at 600 g/t (HKLA), respectively; the trial lasted for 30 days. The results showed that the ratios of feed to gain (F:G) and diarrhea rate of both the HKLA and PC groups were significantly lower compared with the NC and LA groups (p < 0.05); however, there was no significant difference between the HKLA and PC group (p > 0.05). In addition, the average daily weight gain (ADG) of the HKLA group was significantly higher (p < 0.05) than that of the other three groups in terms of growth performance. Finally, 16S rRNA sequencing and metabolome analysis based on fecal samples further elaborated that the addition of heat-killed Lactobacillus acidophilus IFFI 6005 to the feed improved the intestinal microbial diversity and abundance (p < 0.05) and reduced the abundance of pathogenic bacteria (p < 0.05), but it did not affect the abundance of Lactobacillus (p > 0.05). Through the comparison of microbial abundance and metabolite content between the two groups (NC_vs_HKLA), the largest differences were found in six microorganisms and 10 metabolites in the intestine (p < 0.05). These differential metabolites were involved in the digestion, absorption and utilization of protein and starch, as well as in oxidative stress. In summary, addition of heat-killed Lactobacillus acidophilus IFFI 6005 as a new feed additive in piglets has beneficial effects on the growth performance, intestinal bacteria and metabolites, and can be used as an alternative to antibiotics.

Effects of bacteriocin-producing Lactiplantibacillus plantarum on bacterial community and fermentation profile of whole-plant corn silage and its in vitro ruminal fermentation, microbiota, and CH4 emissions

BACKGROUND

Silage is widely used to formulate dairy cattle rations, and the utilization of antibiotics and methane emissions are 2 major problems for a sustainable and environmentally beneficial ruminant production systems. Bacteriocin has received considerable attention because of its potential as an alternative to antibiotics in animal husbandry. However, the impact of bacteriocin-producing lactic acid bacteria on the microbiological conversion process of whole-plant corn silage and rumen fermentation remains limited. The purpose of this study was to assess the effect of 2 class IIa bacteriocin-producing strains Lactiplantibacillus plantarum ATCC14917 and CICC24194 on bacterial community composition and ensiling profiles of whole-plant corn silage and its in vitro rumen fermentation, microbiota, and CH4 emissions.

RESULTS

Both bacteriocin-producing strains increased the lactic acid concentration in silage fermented for 7 d, whereas the lowest lactic acid was observed in the ATCC14917 inoculated silage fermented for 90 d (P < 0.05). The highest DM content was observed in the CICC24194 treatment (P < 0.05), and the silages treated with both strains had the lowest DM loss (P < 0.05). Bacteriocin-producing strains promoted the growth of Levilactobacillus brevis on d 60 of ensiling. In addition, treatment with bacteriocin-producing strains increased the in vitro DM digestibility (P < 0.05) and decreased the CH4 production (P < 0.05). The results of random forest and clustering analyses at the genus level showed that ATCC14917 increased the relative abundance of the influential variable Bacillus compared to that in the control group, whereas CICC24194 decreased the relative abundance of the influential variable Ruminococcaceae UCG-005. The CICC24194 treatment had the lowest total bacterial, fungal, protozoan, and methanogen populations (P < 0.05).

CONCLUSIONS

Both class IIa bacteriocin-producing L. plantarum strains improved the fermentation quality of whole-plant corn silage by regulating the bacterial community composition during ensiling, with CICC24194 being the most effective. Both bacteriocin-producing strains mitigated CH4 production and improved digestibility by modulating the interactions among rumen bacteria, protozoa, methanogens, and the composition of fibrolytic bacteria.

Examining homoacetogens in feces from adult and juvenile kangaroos with the aim of finding competitive strains to hydrogenotrophic methanogens

We examined the microbial populations present in fecal samples of macropods capable of utilizing a mixture of hydrogen and carbon dioxide (70:30) percent. The feces samples were cultured under anaerobic conditions, and production of methane or acetic acids characteristic for methanogenesis and homoacetogenesis was measured. While the feces of adult macropods mainly produced methane from the substrate, the sample from a 2-month-old juvenile kangaroo only produced acetic acid and no methane. The stable highly enriched culture of the joey kangaroo was sequenced to examine the V3 and V4 regions of the 16S rRNA gene. The results showed that over 70% of gene copies belonged to the Clostridia class, with Paraclostridium and Blautia as the most predominant genera. The culture further showed the presence of Actinomyces spp., a genus which has only been identified in the GI tract of macropods in a few studies, and where none, to our knowledge, have been classified as homoacetogenic. The joey kangaroo mixed culture showed a doubling time of 3.54 h and a specific growth rate of 0.199/h, faster than what has been observed for homoacetogenic bacteria in general.

IMPORTANCE

Enteric methane emissions from cattle are a significant contributor to greenhouse gas emissions worldwide. Methane emissions not only contribute to climate change but also represent a loss of energy from the animal's diet. However, methanogens play an important role as hydrogen sink to rumen systems; without it, the performance of hydrolytic organisms diminishes. Therefore, effective strategies of methanogen inhibition would be enhanced in conjunction with the addition of alternative hydrogen sinks to the rumen. The significance of our research is to identify homoacetogens present in the GI tract of kangaroos and to present their performance in vitro, demonstrating their capability to serve as alternatives to rumen methanogens.

Comparative effects of nisin and monensin supplementation on growth performance, rumen fermentation, nutrient digestion, and plasma metabolites of fattening Hu sheep

Introduction

This study was conducted to compare the effects of nisin (NIS) and ionophore antibiotic monensin (MON) on the growth performance, rumen fermentation, nutrient digestion and plasma metabolites of fattening Hu sheep.

Methods

Thirty-six male Hu sheep (23.5 ± 1.0 kg) were divided into two blocks based on BW (low BW and high BW). Sheep within each block were then allotted to 9 pens respectively (two sheep/pen). Pens within each block were randomly assigned to one of three dietary treatments: (1) basal diet (CON); (2) basal diet + 40 mg/kg DM of MON; (3) basal diet + 274.5 mg/kg DM of NIS. The study lasted 9 weeks, with the initial 2 weeks for adaptation and the subsequent 7 weeks for treatment.

Results

The results showed that both NIS and MON addition had no impacts on average daily gain (ADG), dry matter intake (DMI), and feed conservation rate (G:F) of sheep (p > 0.05). The digestibility of ether extract (EE) was lower in the MON-fed and NIS-fed sheep (p < 0.01) than in the CON group, whereas crude protein (CP) digestibility was higher in the MON-fed sheep compared to those fed NIS (p < 0.05). Both NIS and MON supplementation decreased acetate levels and acetate/propionate ratio in the rumen of Hu sheep (p < 0.05). Sheep fed MON exhibited higher total cholesterol concentrations (p < 0.05) compared to the CON and NIS groups. However, there were no significant differences in other plasma metabolites, including blood urea nitrogen (BUN), total bile acid, triglyceride, total protein, albumin, globulin, glucose, etc., among the three groups (p > 0.05).

Discussion

In conclusion, dietary addition of NIS and MON altered the rumen fermentation mode by reducing acetate levels, with no discernible effects on the growth performance of the fattening Hu sheep.

In vitro fermentation end-products and rumen microbiome as influenced by microencapsulated phytonutrient pellets (LEDRAGON) supplementation

The objective of this study was to investigate the effect of microencapsulated bioactive compounds from lemongrass mixed dragon fruit peel pellet (MiEn-LEDRAGON) supplementation on fermentation characteristics, nutrient degradability, methane production, and the microbial diversity using in vitro gas production technique. The study was carried out using a completely randomized design (CRD) with five levels of MiEn-LEDRAGON supplementation at 0, 1, 2, 3, and 4% of the total dry matter (DM) substrate. Supplementation of MiEn-LEDRAGON in the diet at levels of 3 or 4% DM resulted in increased (p < 0.05) cumulative gas production at 96 hours (h) of incubation time, reaching up to 84.842 ml/ 0.5 g DM. Furthermore, supplementation with 3% MiEn-LEDRAGON resulted in higher in vitro nutrient degradability and ammonia-nitrogen concentration at 24 h of the incubation time when compared to the control group (without supplementation) by 5.401% and 11.268%, respectively (p < 0.05). Additionally, supplementation with MiEn-LEDRAGON in the diet led to an increase in the population of Fibrobacter succinogenes at 24 h and Butyrivibrio fibrisolvens at 12 h, while decreasing the population of Ruminococcus albus, Ruminococcus flavefaciens, and Methanobacteriales (p < 0.05). Moreover, supplementation of MiEn-LEDRAGON in the diet at levels of 2 to 4% DM resulted in a higher total volatile fatty acids (VFA) at 24 h, reaching up to 73.021 mmol/L (p < 0.05). Additionally, there was an increased proportion of propionic acid (C3) and butyric acid (C4) at 12 h (p < 0.05). Simultaneously, there was a decrease in the proportion of acetic acid (C2) and the ratio of acetic acid to propionic acid (C2:C3), along with a reduction of methane (CH4) production by 11.694% when comparing to the 0% and 3% MiEn-LEDRAGON supplementation (p < 0.05). In conclusion, this study suggests that supplementing MiEn-LEDRAGON at 3% of total DM substrate could be used as a feed additive rich in phytonutrients for ruminants.

The regulatory mechanism of garlic skin improving the growth performance of fattening sheep through metabolism and immunity

Objective

Garlic skin (GAS) has been proven to improve the growth performance of fattening sheep. However, the mechanism by which GAS affects fattening sheep is not yet clear. The aim of this study is to investigate the effects of adding GAS to feed on the growth performance, rumen and fecal microbiota, serum and urine metabolism, and transcriptomics of rumen epithelial cells in fattening sheep.

Methods

GAS with 80 g/kg dry matter (DM) was added to the diet of fattening sheep to study the effects of GAS on gut microbiota, serum and urine metabolism, and transcriptome of rumen epithelial tissue in fattening sheep. Twelve Hu sheep (body weights; BW, 23.0 ± 2.3 kg and ages 120 ± 3.5 d) were randomly divided into two groups. The CON group was the basal diet, while the GAS group was supplemented with GAS in the basal diet. The trial period was 10 weeks, with the first 2 weeks being the pre-trial period.

Results

The daily average weight gain of fattening sheep in the GAS group was significantly higher than that in the CON group (p < 0.05), and the serum GSH-Px of the GAS group fattening sheep was significantly increased, while MDA was significantly reduced (p < 0.05). Based on the genus classification level, the addition of garlic peel in the diet changed the intestinal microbial composition, and the relative abundance was significantly upregulated by Metanobrevibater (p < 0.05), while significantly downregulated by Akkermansia, Parasutterella, and Guggenheimella (p < 0.05). Metabolomics analysis found that there were 166 significantly different metabolites in serum and 68 significantly different metabolites in urine between the GAS and CON groups (p < 0.05). GAS had an impact on amino acid metabolism, pyrimidine metabolism, methane metabolism, riboflavin metabolism, and unsaturated fatty acid synthesis pathways (p < 0.05). Transcriptome sequencing showed that differentially expressed genes were mainly enriched in immune regulatory function, improving the health of fattening sheep.

Conclusion

Adding GAS can improve the energy metabolism and immune function of fattening sheep by altering gut microbiota, metabolome, and transcriptome, thereby improving the growth performance of fattening sheep.

Interaction between methanotrophy and gastrointestinal nematodes infection on the rumen microbiome of lambs

Complex cross-talk occurs between gastrointestinal nematodes and gut symbiotic microbiota, with consequences for animal metabolism. To investigate the connection between methane production and endoparasites, this study evaluated the effect of mixed infection with Haemonchus contortus and Trichostrongylus colubriformis on methanogenic and methanotrophic community in rumen microbiota of lambs using shotgun metagenomic and real-time quantitative PCR (qPCR). The rumen content was collected from six Santa Inês lambs, (7 months old) before and after 42 days infection by esophageal tube. The metagenomic analysis showed that the infection affected the microbial community structure leading to decreased abundance of methanotrophs bacteria, i.e. α-proteobacteria and β-proteobacteria, anaerobic methanotrophic archaea (ANME), protozoa, sulfate-reducing bacteria, syntrophic bacteria with methanogens, geobacter, and genes related to pyruvate, fatty acid, nitrogen, and sulfur metabolisms, ribulose monophosphate cycle, and Entner-Doudoroff Pathway. Additionally, the abundance of methanogenic archaea and the mcrA gene did not change. The co-occurrence networks enabled us to identify the interactions between each taxon in microbial communities and to determine the reshaping of rumen microbiome associations by gastrointestinal nematode infection. Besides, the correlation between ANMEs was lower in the animal's postinfection. Our findings suggest that gastrointestinal parasites potentially lead to decreased methanotrophic metabolism-related microorganisms and genes.

Differential responses of rumen and fecal fermentation and microbiota of Liaoning cashmere goats after 2-hydroxy-4-(methylthio) butanoic acid isopropyl ester supplementation

The 2-hydroxy-4-(methylthio) butanoic acid isopropyl ester (HMBi), a rumen protective methionine, has been extensively studied in dairy cows and beef cattle and has been shown to regulate gastrointestinal microbiota and improve production performance. However, knowledge of the application of HMBi on cashmere goats and the simultaneous study of rumen and hindgut microbiota is still limited. In this study, HMBi supplementation increased the concentration of total serum protein, the production of microbial protein in the rumen and feces, as well as butyrate production in the feces. The results of PCoA and PERMANOVA showed no significant difference between the rumen microbiota, but there was a dramatic difference between the fecal microbiota of the two groups of Cashmere goats after the HMBi supplementation. Specifically, in the rumen, HMBi significantly increased the relative abundance of some fiber-degrading bacteria (such as Fibrobacter) compared with the CON group. In the feces, as well as a similar effect as in the rumen (increasing the relative abundance of some fiber-degrading bacteria, such as Lachnospiraceae FCS020 group and ASV32), HMBi diets also increased the proliferation of butyrate-producing bacteria (including Oscillospiraceae UCG-005 and Christensenellaceae R-7 group). Overall, these results demonstrated that HMBi could regulate the rumen and fecal microbial composition of Liaoning cashmere goats and benefit the host.

Bioconversion of citrus waste by long-term DMSO-cryopreserved rumen fluid to volatile fatty acids and biogas is feasible: A microbiome perspective

Preserving rumen fluid as the inoculum for anaerobic digestion of food waste is necessary when access to animal donors or slaughterhouses is limited. This study aims to compare two preservation methods relative to fresh ruminal inoculum: (1) cryoprotected with 5% dimethyl sulfoxide (DMSO) and stored at -20 °C and (2) frozen at -20 °C, both for 6 months. The fermentation activity of different inoculum was evaluated by rumen-based in vitro anaerobic fermentation tests (volatile fatty acids, biomass digestibility, and gas production). Citrus pomace was used as the substrate during a 96-h fermentation. The maximum volatile fatty acids, methane production, and citrus pomace digestibility from fresh rumen fluid were not significantly different from rumen fluid preserved with DMSO. Metagenome analysis revealed a significant difference in the rumen microbial composition and functions between fresh rumen fluid and frozen inoculum without DMSO. Storage of rumen fluid using -20 °C with DMSO demonstrated the less difference compared with fresh rumen fluid in microbial alpha diversity and taxa composition. The hierarchical clustering tree of CAZymes showed that DMSO cryoprotected fluid was clustered much closer to the fresh rumen fluid, showing more similarity in CAZyme profiles than frozen rumen fluid. The abundance of functional genes associated with carbohydrate metabolism and methane metabolism did not differ between fresh rumen fluid and the DMSO-20 °C, whereas the abundance of key functional genes significantly decreased in frozen rumen fluid. These findings suggest that using rumen liquid preserved using DMSO at -20 °C for 180 days is a feasible alternative to fresh rumen fluid. This would reduce the need for laboratories to maintain animal donors and/or reduce the frequency of collecting rumen fluid from slaughterhouses.

A comprehensive review on methane's dual role: effects in climate change and potential as a carbon-neutral energy source

The unprecedented population and anthropogenic activity rise have challenged the future look up for shifts in global temperature and climate patterns. Anthropogenic activities such as land fillings, building dams, wetlands converting to lands, combustion of biomass, deforestation, mining, and the gas and coal industries have directly or indirectly increased catastrophic methane (CH4) emissions at an alarming rate. Methane is 25 times more potent trapping heat when compared to carbon dioxide (CO2) in the atmosphere. A rise in atmospheric methane, on a 20-year time scale, has an impact of 80 times greater than that of CO2. With increased population growth, waste generation is rising and is predicted to reach 6 Mt by 2025. CH4 emitted from landfills is a significant source that accounts for 40% of overall global methane emissions. Various mitigation and emissions reduction strategies could significantly reduce the global CH4 burden at a cost comparable to the parallel and necessary CO2 reduction measures, reversing the CH4 burden to pathways that achieve the goals of the Paris Agreement. CH4 mitigation directly benefits climate change, has collateral impacts on the economy, human health, and agriculture, and considerably supports CO2 mitigation. Utilizing the CO2 from the environment, methanogens produce methane and lower their carbon footprint. NGOs and the general public should act on time to overcome atmospheric methane emissions by utilizing the raw source for producing carbon-neutral fuel. However, more research potential is required for green energy production and to consider investigating the untapped potential of methanogens for dependable energy generation.

- Invited Review - Understanding the functionality of the rumen microbiota: searching for better opportunities for rumen microbial manipulation

Rumen microbiota play a central role in the digestive process of ruminants. Their remarkable ability to break down complex plant fibers and proteins, converting them into essential organic compounds that provide animals with energy and nutrition. Research on rumen microbiota not only contributes to improving animal production performance and enhancing feed utilization efficiency but also holds the potential to reduce methane emissions and environmental impact. Nevertheless, studies on rumen microbiota face numerous challenges, including complexity, difficulties in cultivation, and obstacles in functional analysis. This review provides an overview of microbial species involved in the degradation of macromolecules, the fermentation processes, and methane production in the rumen, all based on cultivation methods. Additionally, the review introduces the applications, advantages, and limitations of emerging omics technologies such as metagenomics, metatranscriptomics, metaproteomics, and metabolomics, in investigating the functionality of rumen microbiota. Finally, the article offers a forward-looking perspective on the new horizons and technologies in the field of rumen microbiota functional research. These emerging technologies, with continuous refinement and mutual complementation, have deepened our understanding of rumen microbiota functionality, thereby enabling effective manipulation of the rumen microbial community.

Rumen fermentation and microbiota in Shami goats fed on condensed tannins or herbal mixture

BACKGROUND

Phytochemical compounds can modify the rumen microbiome and improve rumen fermentation. This study evaluated the impact of supplementation with tannin and an herbal mixture containing ginger (Zingiber officinale), garlic (Allium sativum), Artemisia (Artemisia vulgaris), and turmeric (Curcuma longa) on the rumen fermentation and microbiota, and histology of rumen tissue of goats. Eighteen Shami male goats were divided into three groups (n = 6): non-supplemented animals fed the basal diet (C, control); animals fed basal diet and supplemented with condensed tannin (T); and animals fed basal diet and supplemented with herbal mixture (HM). Each animal received a basal diet composed of Alfalfa hay and a concentrate feed mixture.

RESULTS

Group HM revealed higher (P < 0.05) rumen pH, total volatile fatty acids (VFA), acetic, propionic, isobutyric, butyric, isovaleric, and valeric. Principal Co-ordinate analysis (PCoA) showed that rumen microbial communities in the control group and supplemented groups were distinct. The supplementation increased (P < 0.05) the relative abundances of phylum Bacteroidota and Proteobacteria and declined (P < 0.05) Firmicutes and Fibrobacterota. Additionally, the dominant genus Prevotella and Rikenellaceae RC9 gut group were increased (P < 0.05) and the family Ruminococcaceae was declined (P < 0.05) due to the supplementation. The supplementation decreased (P < 0.05) the archaeal genus Methanobrevibacter and increased (P < 0.05) Candidatus Methanomethylophilus. Tannin supplementation in T group shortened the rumen papillae.

CONCLUSIONS

The results revealed that the herbal mixture might be used to alter the rumen microbiota to improve rumen fermentation.

Effect of Replacing Corn Meal with Winged Bean Tuber (Psophocarpus tetragonolobus) Pellet on Gas Production, Ruminal Fermentation, and Degradability Using In Vitro Gas Technique

The objective of this study is to evaluate the effects of replacing corn meal in ruminant diets with winged bean (Psophocarpus tetragonolobus) tubers (WBT) on ruminal fermentation, gas production parameters, and in vitro degradability. The study employed a completely random design (CRD) in its execution. The experimental design employed was a completely randomized design (CRD), featuring eleven levels of corn meal substitution with winged bean tubers pellet (WBTP) at 0%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100%. The levels were grouped into four categories of replacement: control (0% in the diet), low levels (10%, 20%, and 30% in the diet), medium levels (40%, 50%, 60%, and 70% in the diet), and high levels (80%, 90%, and 100% in the diet). The experimental results indicated that substituting corn meal with WBTP at moderate and high levels in the diet could improve the performance of the fermentation process by increasing the gas production rate constant from the insoluble fraction (p < 0.01). The IVDMD exhibited a higher degree of in vitro degradation after 12 h (h), with the mean value being higher in the high group compared to the medium until the high group (p < 0.05). At the 4 h mark, the groups that substituted corn meal with WBTP exhibited a decrease in pH value (p < 0.05) in comparison to the control group. The substitution of corn meal with WBTP resulted in the lowest protozoal count after 8 h in the median group (p < 0.05). A significant difference in the effect of WBTP on total volatile fatty acid (TVFA) concentration was observed at 8 h after incubation (p < 0.05). The medium and high levels of WBTP replacement resulted in the lowest TVFA concentration at 8 h (p < 0.05). The mean proportion of acetic acid (C2) linearly declined and was lowest when a high level of WBTP replaced cornmeal (p < 0.05). The concentration of propionic acid (C3) at 8 h after incubation and average values were linearly significantly different when various levels of WBTP were utilized. Replacing corn meal with WBTP at a high level showed the highest concentration of C3. Moreover, substituting medium and high concentrations of WBTP for corn meal resulted in a significant reduction in both the C2:C3 ratio at 8 h and the mean value (p < 0.05). In conclusion, WBTP exhibits a nutritional composition that is advantageous and may be an energetic substitute for corn meal.

Characterization of the Ruminal Microbiome of Water Buffaloes (Bubalus bubalis) Kept in Different Ecosystems in the Eastern Amazon

Increasing the efficiency of rumen fermentation is one of the main ways to maximize the production of ruminants. It is therefore important to understand the ruminal microbiome, as well as environmental influences on that community. However, there are no studies that describe the ruminal microbiota in buffaloes in the Amazon. The objective of this study was to characterize the rumen microbiome of the water buffalo (Bubalus bubalis) in the eastern Amazon in the dry and rainy seasons in three grazing ecosystems: Baixo Amazonas (BA), Continente do Pará (CP), Ilha do Marajó (IM), and in a confinement system: Tomé-Açu (TA). Seventy-one crossbred male buffaloes (Murrah × Mediterranean) were used, aged between 24 and 36 months, with an average weight of 432 kg in the rainy season and 409 kg in the dry season, and fed on native or cultivated pastures. In the confinement system, the feed consisted of sorghum silage, soybean meal, wet sorghum premix, and commercial feed. Samples of the diet from each ecosystem were collected for bromatological analysis. The collections of ruminal content were carried out in slaughterhouses, with the rumen completely emptied and homogenized, the solid and liquid fractions separated, and the ruminal pH measured. DNA was extracted from the rumen samples, then sequenced using Restriction Enzyme Reduced Representation Sequencing. The taxonomic composition was largely similar between ecosystems. All 61 genera in the reference database were recognized, including members of the domains Bacteria and Archaea. The abundance of 23 bacterial genera differed significantly (p < 0.01) between the Tomé-Açu confinement and other ecosystems. Bacillus, Ruminococcus, and Bacteroides had lower abundance in samples from the Tomé-Açu system. Among the Archaea, the genus Methanomicrobium was less abundant in Tomé-Açu, while Methanosarcina was more abundant. There was a difference caused by all evaluated factors, but the diet (available or offered) was what most influenced the ruminal microbiota.

Holistic View and Novel Perspective on Ruminal and Extra-Gastrointestinal Methanogens in Cattle

Despite the extensive research conducted on ruminal methanogens and anti-methanogenic intervention strategies over the last 50 years, most of the currently researched enteric methane (CH4) abatement approaches have shown limited efficacy. This is largely because of the complex nature of animal production and the ruminal environment, host genetic variability of CH4 production, and an incomplete understanding of the role of the ruminal microbiome in enteric CH4 emissions. Recent sequencing-based studies suggest the presence of methanogenic archaea in extra-gastrointestinal tract tissues, including respiratory and reproductive tracts of cattle. While these sequencing data require further verification via culture-dependent methods, the consistent identification of methanogens with relatively greater frequency in the airway and urogenital tract of cattle, as well as increasing appreciation of the microbiome-gut-organ axis together highlight the potential interactions between ruminal and extra-gastrointestinal methanogenic communities. Thus, a traditional singular focus on ruminal methanogens may not be sufficient, and a holistic approach which takes into consideration of the transfer of methanogens between ruminal, extra-gastrointestinal, and environmental microbial communities is of necessity to develop more efficient and long-term ruminal CH4 mitigation strategies. In the present review, we provide a holistic survey of the methanogenic archaea present in different anatomical sites of cattle and discuss potential seeding sources of the ruminal methanogens.

Rumen Lachnospiraceae isolate NK3A20 exhibits metabolic flexibility in response to substrate and coculture with a methanogen

Hydrogen (H2) is the primary electron donor for methane formation in ruminants, but the H2-producing organisms involved are largely uncharacterized. This work integrated studies of microbial physiology and genomics to characterize rumen bacterial isolate NK3A20 of the family Lachnospiraceae. Isolate NK3A20 was the first recognized isolate of the NK3A20 group, which is among the ten most abundant bacterial genera in 16S rRNA gene surveys of rumen microbiota. NK3A20 produced acetate, butyrate, H2, and formate from glucose. The end product ratios varied when grown with different substrates and at different H2 partial pressures. NK3A20 produced butyrate as a major product using glucose or under high H2 partial pressures and switched to mainly acetate in the presence of galacturonic acid (an oxidized sugar) or in coculture with a methanogen. Growth with galacturonic acid was faster at elevated H2 concentrations, while elevated H2 slowed growth with glucose. Genome analyses revealed the presence of multiple hydrogenases including a membrane-bound Ech hydrogenase, an electron bifurcating butyryl-CoA dehydrogenase (Bcd-Etf), and an Rnf complex that may be involved in modulating the observed metabolic pathway changes, providing insight into H2 formation in the rumen. IMPORTANCE The genus-level NK3A20 group is one of the ten most abundant genera of rumen bacteria. Like most of the rumen bacteria that produce the hydrogen that is converted to methane in the rumen, it is understudied, without any previously characterized isolates. We investigated isolate NK3A20, a cultured member of this genus, and showed that it modulates hydrogen production in response to its growth substrates and the hydrogen concentration in its environment. Low-hydrogen concentrations stimulated hydrogen formation, while high concentrations inhibited its formation and shifted the fermentation to more reduced organic acid products. We found that growth on uronic acids, components of certain plant polymers, resulted in low hydrogen yields compared to glucose, which could aid in the selection of low-methane feeds. A better understanding of the major genera that produce hydrogen in the rumen is part of developing strategies to mitigate biogenic methane emitted by livestock agriculture.

Ruminal and feces metabolites associated with feed efficiency, water intake and methane emission in Nelore bulls

The objectives of this study were twofold: (1) to identify potential differences in the ruminal and fecal metabolite profiles of Nelore bulls under different nutritional interventions; and (2) to identify metabolites associated with cattle sustainability related-traits. We used different nutritional interventions in the feedlot: conventional (Conv; n = 26), and by-product (ByPr, n = 26). Thirty-eight ruminal fluid and 27 fecal metabolites were significantly different (P < 0.05) between the ByPr and Conv groups. Individual dry matter intake (DMI), residual feed intake (RFI), observed water intake (OWI), predicted water intake (WI), and residual water intake (RWI) phenotypes were lower (P < 0.05) in the Conv group, while the ByPr group exhibited lower methane emission (ME) (P < 0.05). Ruminal fluid dimethylamine was significantly associated (P < 0.05) with DMI, RFI, FE (feed efficiency), OWI and WI. Aspartate was associated (P < 0.05) with DMI, RFI, FE and WI. Fecal C22:1n9 was significantly associated with OWI and RWI (P < 0.05). Fatty acid C14:0 and hypoxanthine were significantly associated with DMI and RFI (P < 0.05). The results demonstrated that different nutritional interventions alter ruminal and fecal metabolites and provided new insights into the relationship of these metabolites with feed efficiency and water intake traits in Nelore bulls.

Methane reduction by quercetin, tannic and salicylic acids: influence of molecular structures on methane formation and fermentation in vitro

Plant secondary metabolites (PSMs) can potentially reduce ruminal methane formation. However, related to differences in their molecular structures, it is not yet clear what causes an anti-methanogenic effect. In an in vitro system simulating rumen fermentation, we investigated the impact of eight compounds with distinct chemical characteristics (gallic and salicylic acids, tannic acid, catechin, epicatechin, quercetin, rutin, and salicin) when added to a basal feed (maize silage) at a concentration of 12% of the feed dry matter. After 48 h of incubation in buffered rumen fluid, methane production was significantly lowered by quercetin (43%), tannic acid (39%) and salicylic acid (34%) compared to the control (maize silage alone) and without changes in total volatile fatty acid production during fermentation. No other PSM reduced methane formation as compared to control but induced significant differences on total volatile fatty acid production. The observed differences were related to lipophilicity, the presence of double bond and carbonyl group, sugar moieties, and polymerization of the compounds. Our results indicate the importance of distinct molecular structures of PSMs and chemical characteristics for methane lowering properties and volatile fatty acid formation. Further systematic screening studies to establish the structure-function relationship between PSMs and methane reduction are warranted.

Marine Microalgae as a Nutritive Tool to Mitigate Ruminal Greenhouse Gas Production: In Vitro Fermentation Characteristics of Fresh and Ensiled Maize (Zea mays L.) Forage

The aim of the present study was to evaluate the effects of marine microalgae (Dunaliella salina) as a food additive on biogas (BG), methane (CH4), carbon monoxide (CO), and hydrogen sulfide (H2S) production kinetics, as well as in in vitro rumen fermentation and the CH4 conversion efficiency of different genotypes of maize (Zea mays L.) and states of forage. The treatments were characterized by the forage of five maize genotypes (Amarillo, Montesa, Olotillo, Tampiqueño, and Tuxpeño), two states of forage (fresh and ensiled), and the addition of 3% (on DM basis) of microalgae (with and without). The parameters (b = asymptotic production, c = production rate, and Lag = delay phase before gas production) of the production of BG, CH4, CO, and H2S showed an effect (p < 0.05) of the genotype, the state of the forage, the addition of the microalgae, or some of its interactions, except for the time in the CO delay phase (p > 0.05). Moreover, the addition of microalgae decreased (p < 0.05) the production of BG, CH4, and H2S in most of the genotypes and stages of the forage, but the production of CO increased (p < 0.05). In the case of fermentation characteristics, the microalgae increased (p < 0.05) the pH, DMD, SCFA, and ME in most genotypes and forage states. With the addition of the microalgae, the fresh forage from Olotillo obtained the highest pH (p < 0.05), and the ensiled from Amarillo, the highest (p < 0.05) DMD, SCFA, and ME. However, the ensiled forage produced more (p < 0.05) CH4 per unit of SFCA, ME, and OM, and the microalgae increased it (p < 0.05) even more, and the fresh forage from Amarillo presented the highest (p < 0.05) quantity of CH4 per unit of product. In conclusion, the D. salina microalga showed a potential to reduce the production of BG, CH4, and H2S in maize forage, but its effect depended on the chemical composition of the genotype and the state of the forage. Despite the above, the energy value of the forage (fresh and ensiled) improved, the DMD increased, and in some cases, SCFA and ME also increased, all without compromising CH4 conversion efficiency.

Dietary Ruminant Enteric Methane Mitigation Strategies: Current Findings, Potential Risks and Applicability

This review examines the current state of knowledge regarding the effectiveness of different dietary ruminant enteric methane mitigation strategies and their modes of action together with the issues discussed regarding the potential harms/risks and applicability of such strategies. By investigating these strategies, we can enhance our understanding of the mechanisms by which they influence methane production and identify promising approaches for sustainable mitigation of methane emissions. Out of all nutritional strategies, the use of 3-nitrooxypropanol, red seaweed, tannins, saponins, essential oils, nitrates, and sulfates demonstrates the potential to reduce emissions and receives a lot of attention from the scientific community. The use of certain additives as pure compounds is challenging under certain conditions, such as pasture-based systems, so the potential use of forages with sufficient amounts of plant secondary metabolites is also explored. Additionally, improved forage quality (maturity and nutrient composition) might help to further reduce emissions. Red seaweed, although proven to be very effective in reducing emissions, raises some questions regarding the volatility of the main active compound, bromoform, and challenges regarding the cultivation of the seaweed. Other relatively new methods of mitigation, such as the use of cyanogenic glycosides, are also discussed in this article. Together with nitrates, cyanogenic glycosides pose serious risks to animal health, but research has proven their efficacy and safety when control measures are taken. Furthermore, the risks of nitrate use can be minimized by using probiotics. Some of the discussed strategies, namely monensin or halogenated hydrocarbons (as pure compounds), demonstrate efficacy but are unlikely to be implemented widely because of legal restrictions.

Influence of Parturition on Rumen Bacteria and SCFAs in Holstein Cows Based on 16S rRNA Sequencing and Targeted Metabolomics

The rumen fluids from ten cows at Day 3~5 before calving and Day 0 after calving were collected to analyze the composition and quantity of bacterial communities and concentrations of SCFAs. The results showed that the relative abundances of unidentified Lachnospiraceae, Acetitomaculum, Methanobrevibacter, Olsenella, Syntrophococcus, Lachnospira, and Lactobacillus genera were significant increased (p < 0.05), while that of unidentified-Prevotellaceae was notably decreased after calving (p < 0.05). In addition, the concentrations of acetic acid, propionic acid, butyric acid, and caproic acid obviously decreased after calving (p < 0.01). Our findings show that parturition altered the rumen microbiota and their fermentation ability in dairy cows. This study defines a rumen bacteria and metabolic profile of SCFAs associated with parturition in dairy cows.

Effect of Inoculating Two Bacteriocin-Producing Lactiplantibacillus plantarum Strains at Ensiling on In Vitro Rumen Fermentation and Methane Emissions of Alfalfa Silage with Two Dry Matter Contents

The objective of this study was to investigate the effects of inoculating two bacteriocin-producing strains, Lactiplantibacillus plantarum ATCC14917 and LP1-4, at ensiling on the in vitro ruminal fermentation characteristics and methane production of alfalfa silage with two dry matter (DM)contents. Before ensiling, fresh alfalfa was wilted to a moderate DM content (355 g/kg) and a high DM content (428 g/kg). The wilted alfalfa was treated with (1) distilled water (control), (2) commercial strain L. plantarum MTD/1 (MTD/1), (3) bacteriocin-producing L. plantarum ATCC14917 (ATCC14917), and (4) a bacteriocin-like substance producing L. plantarum LP1-4 (LP1-4) at 1 × 10⁵ colony forming units (CFU)/g fresh weight. After 90 d of ensiling, the silages were used for in vitro rumen fermentation. Inoculation with the two bacteriocin-producing strains at ensiling remarkably reduced (p < 0.05) in vitro ruminal CH₄ production and enhanced DM digestibility compared with the control group regardless of DM content. For silages with high DM content, inoculation with the bacteriocin-producing strains even increased (p < 0.05) in vitro ruminal total volatile fatty acid production. Therefore, the bacteriocin-producing inoculants have a great potential to mitigate ruminal methane emission but without an adverse effect on rumen fermentation of the inoculated alfalfa silage.

Trait-Based Method of Quantitative Assessment of Ecological Functional Groups in the Human Intestinal Microbiome

We propose the trait-based method for quantifying the activity of functional groups in the human gut microbiome based on metatranscriptomic data. It allows one to assess structural changes in the microbial community comprised of the following functional groups: butyrate-producers, acetogens, sulfate-reducers, and mucin-decomposing bacteria. It is another way to perform a functional analysis of metatranscriptomic data by focusing on the ecological level of the community under study. To develop the method, we used published data obtained in a carefully controlled environment and from a synthetic microbial community, where the problem of ambiguity between functionality and taxonomy is absent. The developed method was validated using RNA-seq data and sequencing data of the 16S rRNA amplicon on a simplified community. Consequently, the successful verification provides prospects for the application of this method for analyzing natural communities of the human intestinal microbiota.

Could propionate formation be used to reduce enteric methane emission in ruminants?

To meet the increasing demand for meat and milk, the livestock industry has to increase its production. Without improving its efficiency, increased livestock, especially ruminant animals, will worsen the environmental damage, mainly from enteric CH₄ emission. Enteric CH₄ emission from ruminants not only exacerbates the global greenhouse effect but also reduces feed energy efficiency for the animals. The rumen disposes of metabolic hydrogen ([H]) primarily through methanogenesis and propionate formation. Theoretically, redirecting [H] from methanogenesis to propionate formation to reduce CH₄ production could be a promising method for reducing greenhouse gas emission from ruminants, and may also increase animal productivity. However, the feasibility of such a shifting has never been synthetically discussed. Thus, the objectives of this review are to provide a brief overview of the biochemical pathways for disposal of H₂ in the rumen, to analyze current feeding strategies that potentially promote propionate formation and their effects on methanogenesis, and to deliberate the challenge and opportunity associated with propionate formation as a sink to store the [H] shifting from enteric CH₄ inhibition.

Expanding the valorization of waste mushroom substrates in agricultural production: progress and challenges

Waste mushroom substrate (WMS) generated in large quantities from mushroom production process has caused severe environmental pollution. As a sustainable resource, the valorization of WMS in the agricultural field has attracted attention due to the abundant active components. A comprehensive review of valorization of WMS in agricultural production is meaningful to promote the further utilization of this resource. This paper provided an overview of the valorization in sustainable agricultural production using WMS, including animal and crop farming improvement, and agricultural environmental restoration. Moreover, the limitations and the possible development directions of WMS in agricultural production were discussed. Different sustainable cycle models for WMS in agricultural production were proposed. The aim of this review is to provide a feasible solution for the favorable treatment of WMS and improvement of agricultural production quality.

Fermentation of increasing ratios of grain starch and straw fiber: effects on hydrogen allocation and methanogenesis through in vitro ruminal batch culture

Grain starch has a faster rate of rumen fermentation than straw fiber and causes a rapid increase in ruminal molecular hydrogen (H₂) partial pressure, which may promote other H₂ sinks to compete H₂ away from methanogenesis. The study was designed to investigate the effects of increasing ratios of grain starch to straw fiber on hydrogen allocation and methanogenesis through in vitro ruminal batch incubation. Corn grain and corn straw were employed as starch and fiber source respectively. Seven treatments were the ratios of corn grain to corn straw (RGS) being 0:6, 1:5, 2:4, 3:3, 4:2, 5:1, and 6:0. Elevating RGS increased dry matter (DM) degradation and decreased methane (CH₄) and hydrogen gas (gH₂) production relative to DM degraded. Elevating RGS increased volatile fatty acid (VFA) concentration, propionate molar percentage and microbial protein (MCP) concentration, decreased acetate molar percentage, acetate to propionate ratio and estimated net metabolic hydrogen ([H]) production relative to DM degraded. Elevating RGS decreased the molar percentage of [H] utilized for CH₄ and gH₂ production. In summary, increasing ratios of grain starch to straw fiber altered rumen fermentation pathway from acetate to propionate production, reduced the efficiency of [H] production with the enhancement of MCP synthesis, and led to a reduction in the efficiency of CH₄ and gH₂ production.

Prevotella: A Key Player in Ruminal Metabolism

Ruminants are foregut fermenters that have the remarkable ability of converting plant polymers that are indigestible to humans into assimilable comestibles like meat and milk, which are cornerstones of human nutrition. Ruminants establish a symbiotic relationship with their microbiome, and the latter is the workhorse of carbohydrate fermentation. On the other hand, during carbohydrate fermentation, synthesis of propionate sequesters H, thus reducing its availability for the ultimate production of methane (CH4) by methanogenic archaea. Biochemically, methane is the simplest alkane and represents a downturn in energetic efficiency in ruminants; environmentally, it constitutes a potent greenhouse gas that negatively affects climate change. Prevotella is a very versatile microbe capable of processing a wide range of proteins and polysaccharides, and one of its fermentation products is propionate, a trait that appears conspicuous in P. ruminicola strain 23. Since propionate, but not acetate or butyrate, constitutes an H sink, propionate-producing microbes have the potential to reduce methane production. Accordingly, numerous studies suggest that members of the genus Prevotella have the ability to divert the hydrogen flow in glycolysis away from methanogenesis and in favor of propionic acid production. Intended for a broad audience in microbiology, our review summarizes the biochemistry of carbohydrate fermentation and subsequently discusses the evidence supporting the essential role of Prevotella in lignocellulose processing and its association with reduced methane emissions. We hope this article will serve as an introduction to novice Prevotella researchers and as an update to others more conversant with the topic.

Lentilactobacillus buchneri Preactivation Affects the Mitigation of Methane Emission in Corn Silage Treated with or without Urea

The aim of this study was to investigate the effect of different forms of Lentilactobacillus buchneri on the in vitro methane production, fermentation characteristics, nutritional quality, and aerobic stability of corn silage treated with or without urea. The following treatments were applied prior to ensiling: (1) no urea treatment and LB; (2) no urea treatment+freeze dried LB; (3) no urea treatment+preactivated LB; (4) with urea treatment+no LB; (5) with urea treatment+freeze dried LB; (6) with urea treatment+preactivated. LB was applied at a rate of 3 × 108 cfu/kg on a fresh basis, while urea was applied at a rate of 1% on the basis of dry matter. Data measured at different time points were analyzed according to a completely randomized design, with a 2 × 3 × 5 factorial arrangement of treatments, while the others were analyzed with a 2 × 3 factorial arrangement. Preactivated LB was more effective than freeze-dried LB in reducing silage pH, ammonia nitrogen, cell-wall components, yeast count, and carbon dioxide production, as well as increasing lactic acid and residual water-soluble carbohydrate and aerobic stability (p < 0.0001). A significant reduction in the methane ratio was observed after 24 h and 48 h incubation with preactivated forms of LB (p < 0.001). The results indicated that preactivated LB combined with urea improved fermentation characteristics, nutritional quality, and aerobic stability and reduced the methane ratio of corn silages.

Enhanced carbon dioxide biomethanation with hydrogen using anaerobic granular sludge and metal-organic frameworks: Microbial community response and energy metabolism analysis

In this work, metal-organic frameworks (MOFs) were prepared to evaluate its impact on carbon dioxide (CO₂) biomethanization during anaerobic degradation (AD). The results showed that MOFs significantly improved the CO₂ biomethanation efficiency, especially in the AD reactors using a concentration of 1.0 g/L MOFs. Furthermore, MOFs promoted direct interspecific electron transfer and alleviated the hydrogen competition of bacteria. Meanwhile, hydrogenotrophic methanogens were enriched in the AD reactors with MOFs. After the addition of MOFs, there was 3.28 times and 3.41 times increase in the abundance of metabolic functions related to methanogenesis by CO₂ reduction with hydrogen and dark hydrogen oxidation, respectively. There was an increased abundance of all genes that encode the key enzymes used in methane metabolism. However, functional genes involved in nitrate reduction had their expressions inhibited. The work may offer a contribution to helping the industry achieve the carbon capture and utilization policy.

Comparisons of Ramie and Corn Stover Silages: Effects on Chewing Activity, Rumen Fermentation, Microbiota and Methane Emissions in Goats

The study aimed to investigate the nutritional value of ramie (Boehmeria nivea) silage, and its consequences for chewing activity, rumen fermentation, and enteric methane (CH4) emissions in goats, by comparing it with corn stover (CS) silage. An in vitro ruminal experiment was firstly performed to investigate the substrate degradation and fermentation of CS and ramie silage. The ramie silage diet was formulated by replacing 60% of CS silage with ramie silage (dry matter (DM) basis). Eight female Xiangdong Black goats (a local breed in Southern China, 1 to 1.2 years of age) with BW of 21.0 ± 1.05 kg were used for this experiment and were randomly assigned to either one of the two dietary treatments in a cross-over design. The ramie silage had higher crude protein (CP) and ash content and lower hemicellulose content, together with decreased (p < 0.05) nutrient degradation and methane production and increased (p < 0.05) acetate molar percentage and acetate to propionate ratio through in vitro ruminal fermentation. Feeding the ramie silage diet did not alter feed intake (p > 0.05), decreased (p < 0.05) nutrient digestibility, and increased (p < 0.05) chewing activity and rumination activity, with reductions (p < 0.05) in eating activity and idle activity. Although feeding the ramie silage diet caused a greater (p < 0.05) molar percentage of acetate and lower molar percentage of propionate, it decreased the rumen-dissolved CH4 concentration and enteric CH4 emissions (p < 0.05). Feeding the ramie silage diet did not alter (p > 0.05) the population of bacteria, protozoa, and fungi; it increased the 16S rRNA gene copies of Ruminococcus flavefaciens (p < 0.05). Further 16SrRNA gene amplicon analysis indicated a distinct bacterial composition between the two treatments (p < 0.05). Feeding the ramie silage diet led to a lower abundance of genera Lawsonibacter, Sedimentibacter, Saccharofermentans, Sediminibacterium, and Bifidobacterium (p < 0.05). Ramie can be an alternative forage resource to stimulate chewing activity and reduce CH4 emissions in ruminants.

Effect of Autochthonous Nepalese Fruits on Nutrient Degradation, Fermentation Kinetics, Total Gas Production, and Methane Production in In-Vitro Rumen Fermentation

The objective of this study was to determine the effect of autochthonous Nepalese fruits on nutrient degradation, fermentation kinetics, total gas production, and methane production in in-vitro rumen fermentation. The fruits of Terminalia chebula (HA), Terminalia bellirica (BA), and Triphala churna (TC), a commercial mixture with equal parts (33.3% DM basis) of Phyllanthus emblica, Terminalia bellirica, and Terminalia chebula, were used. These were tested at three inclusion levels of 20% 40% and 100% of the total sample (as dry matter) in maize silage (MS). MS was used as a control (0% additive). These 10 treatments were tested for two 48-h incubations with quadruplicate samples using rumen fluid from 2 heifers. Total gas production (TGP: mL at standard temperature and pressure (STP)/g DM), methane production (expressed as % and mL/g DM), and volatile fatty acids were determined. After incubations, the filtrate was used to measure pH and volatile fatty acids (VFA), while the residue was used to measure degraded dry matter (dDM) and calculate the partitioning factor (PF48) and theoretical short-chain fatty acid concentration (tVFA). Rumen fluid pH linearly (p < 0.01) decreased in all treatments with increasing dose during fermentation. The CH4% was less in all three treatments with 100% autochthonous plants than in control, but there were no significant linear or quadratic effects for increasing BA, HA, and TC doses. The PF48 increased for all treatments with a significant linear and quadratic effect (p < 0.05) of increasing dose. Compared to MS, the inclusion of autochthonous plants increased the total volatile fatty acids, with no significant dose effects. The tVFA linearly decreased (p > 0.05) with an increasing dose of BA and HA. All treatments showed quadratic effects on tVFA (p < 0.05) with increasing dose. Increasing TC dose linearly (p < 0.05) and quadratically (p < 0.05) increased total VFA, while increasing HA dose had only a quadratic (p < 0.05) effect on total VFA. All treatments reduced total gas production (TGP) and methane concentration (CH4%) when compared to MS. The tested autochthonous fruits can be used as additives with a basal feed diet to reduce enteric methane emissions. The most effective anti-methanogenic treatment was 40% HA, which resulted in 18% methane reduction.

Nutraceutical Enrichment of Animal Feed by Filamentous Fungi Fermentation

There is an urgent need for improvements in animal production, particularly for ruminants, such that more sustainable and efficient processes are developed for obtaining more nutritious and efficient feeds. Filamentous fungi can add value to residual plant biomass, and may also have the potential to produce metabolites and enrich plant biomasses used in animal nutrition, converting them into nutraceutical sources. Thus, in this work, filamentous fungal fermentation of ruminant feed biomasses commonly used in Brazil was performed, and the enrichment for bioactive metabolites was tested. For this, Fistulina hepatica, Ganoderma lucidum, Pleurotus pulmonarius, Panus lecomtei, and Aspergillus terreus were grown for 28 days on different substrates: starchy grains- (sorghum, oat, and corn), fibrous substrates (coast-cross, rice husk, and moringa plant) and protein-rich substrates (cottonseed cake and pigeon pea plant). Fermented substrates were evaluated for laccase activity, crude protein, β-glucan, and lovastatin content. The highest growth rate was observed for G. lucidum in oat substrate (OT-01) (0.708 ± 0.035 cm/day) and F. hepatica in oat + coast-cross + pigeon pea treatment (OT-10) (0.607 ± 0.012 cm/day). High laccase activity was observed for P. lecomtei grown in starchy grain + moringa + pigeon pea substrate, reaching an activity of 416.8 ± 20.28 U/g. A. terreus growth in ST-09 (sorghum + pigeon pea) showed higher protein (15.3 ± 0.46%), β-glucan (503.56 ± 8.6 mg/g) and lovastatin (1.10 ± 0.17 mg/g) content compared to untreated substrates. These results demonstrate that filamentous fungi are an alternative for nutraceutical enrichment of ruminant feed biomasses. To the best of our knowledge, this is the first report in which P. lecomtei and F. hepatica are evaluated for their ability to be cultivated in ruminant feed substrates from Brazil.

The Gut Microbiota Determines the High-Altitude Adaptability of Tibetan Wild Asses (Equus kiang) in Qinghai-Tibet Plateau

It was acknowledged long ago that microorganisms have played critical roles in animal evolution. Tibetan wild asses (TWA, Equus kiang) are the only wild perissodactyls on the Qinghai-Tibet Plateau (QTP) and the first national protected animals; however, knowledge about the relationships between their gut microbiota and the host's adaptability remains poorly understood. Herein, 16S rRNA and meta-genomic sequencing approaches were employed to investigate the gut microbiota–host associations in TWA and were compared against those of the co-resident livestock of yak (Bos grunnies) and Tibetan sheep (Ovis aries). Results revealed that the gut microbiota of yak and Tibetan sheep underwent convergent evolution. By contrast, the intestinal microflora of TWA diverged in a direction enabling the host to subsist on sparse and low-quality forage. Meanwhile, high microbial diversity (Shannon and Chao1 indices), cellulolytic activity, and abundant indicator species such as Spirochaetes, Bacteroidetes, Prevotella_1, and Treponema_2 supported forage digestion and short-chain fatty acid production in the gut of TWA. Meanwhile, the enterotype identification analysis showed that TWA shifted their enterotype in response to low-quality forage for a better utilization of forage nitrogen and short-chain fatty acid production. Metagenomic analysis revealed that plant biomass degrading microbial consortia, genes, and enzymes like the cellulolytic strains (Prevotella ruminicola, Ruminococcus flavefaciens, Ruminococcus albus, Butyrivibrio fibrisolvens, and Ruminobacter amylophilus), as well as carbohydrate metabolism genes (GH43, GH3, GH31, GH5, and GH10) and enzymes (β-glucosidase, xylanase, and β-xylosidase, etc.) had a significantly higher enrichment in TWA. Our results indicate that gut microbiota can improve the adaptability of TWA through plant biomass degradation and energy maintenance by the functions of gut microbiota in the face of nutritional deficiencies and also provide a strong rationale for understanding the roles of gut microbiota in the adaptation of QTP wildlife when facing harsh feeding environments.

Effects of Supplementing Finishing Goats with Mitragyna speciosa (Korth) Havil Leaves Powder on Growth Performance, Hematological Parameters, Carcass Composition, and Meat Quality

The objective of this study was to see how dried Mitragyna speciosa Korth leaves (DKTL) affected growth, hematological parameters, carcass characteristics, muscle chemical composition, and fatty acid profile in finishing goats. In a randomized complete block design, twenty crossbred males (Thai Native x Boer) weaned goats (17.70 ± 2.50 kg of initial body weight (BW)) were provided to the experimental animals (5 goats per treatment) for 90 days. Individual dietary treatments of 0, 2.22, 4.44, and 6.66 g/d of DKTL on a dry matter basis were given to the goats. The diets were provided twice daily as total mixed rations ad libitum. In comparison to the control diet, DKTL supplementation had no effect on BW, average daily gain (ADG), feed conversion ratio (FCR), carcass composition, meat pH, or meat color (p > 0.05). After DKTL treatment, the hot carcass weight, longissimus muscle area, oleic acid (C18:1n9), monounsaturated fatty acid (MUFA), and protein content increased, but saturated fatty acids (SFA) and ether extract decreased (p < 0.05). To summarize, DKTL supplementation can improve goat meat quality.

Decreasing ruminal methane production through enhancing the sulfate reduction pathway

Methane (CH₄) production from ruminants accounts for 16% of the global greenhouse gas emissions and represents 2% to 12% of feed energy. Mitigating CH₄ production from ruminants is of great importance for sustainable development of the ruminant industry. H₂ is the primary substrate for CH₄ production in the processes of ruminal methanogenesis. Sulfate reducing bacteria are able to compete with methanogens for H₂ in the rumen, and consequently inhibit the methanogenesis. Enhancing the ruminal sulfate reducing pathway is an important approach to mitigate CH₄ emissions in ruminants. The review summarized the effects of sulfate and elemental S on ruminal methanogenesis, and clarified the related mechanisms through the impacts of sulfate and elemental S on major ruminal sulfate reducing bacteria. Enhancing the activities of the major ruminal sulfate reducing bacteria including Desulfovibrio, Desulfohalobium and Sulfolobus through dietary sulfate addition, elemental S and dried distillers grains with solubles can effectively decrease the ruminal CH₄ emissions. Suitable levels of dietary addition with different S sources for reducing the ruminal CH₄ production, as well as maintaining the performance and health of ruminants, need to be investigated in the future.

Diet Supplementation With Sulfur Amino Acids Modulated Fermentation Metabolome and Gut Microbiome in Goats

Dietary amino acids shift hydrogen metabolism to an alternative hydrogen sink consisting of dissolved hydrogen sulfur (dH2S) rather than methanogenesis; and influences the fermentation metabolome and microbiome associated with particles and liquid fractions in gut regions (foregut, small intestine, and hindgut) of goats. A completely randomized block design with a total of 20 goats (5 goats per treatment) was used to conduct the trial. The goats were fed on a diet that consisted of a concentrated mixture with maize stover roughage (50:50, on a dry matter basis) and randomly assigned to one of the four treatments: without amino acid supplementation (a basal diet), a basal diet supplemented with methionine (Met), a basal diet supplemented with lysine (Lys), and a basal diet supplemented with methionine and lysine (ML). Goats fed Met alone or in combination had less acetate, acetate to propionate ratio, and greater propionate (p &lt; 0.05) in the foregut and hindgut than those fed control or Lys. Nonetheless, the goats fed on the amino acid supplements had higher levels of branched-chain VFA (p &lt; 0.05) in the foregut and hindgut than the control goats. Goats fed on ML had the highest ammonia (p &lt; 0.01), followed by Met or Lys, both in the foregut and hindgut, compared with the control. Those fed on Met alone or in combination, had lower dH2, dCH4 (p &lt; 0.01), and higher dH2S (p &lt; 0.01) in the foregut and hindgut than the control or Lys. The goats that were fed on Met alone or in combination, had higher 16S rRNA gene copies of total bacteria, methanogens, and 18S rRNA gene copies of protozoa, fungi, and fiber-utilizing bacterial species (p &lt; 0.01) associated with particles vs. liquid, both in the foregut and hindgut than the control goats. This study gives insights into the use of sulfur-containing amino acids, as an alternative dietary mitigation strategy of methanogenesis in ruminants and highlights the need for further research in this direction.

Enhancing Rumen Fermentation Characteristic and Methane Mitigation Using Phytonutrient Pellet in Beef Cattle

The objective of this experiment was to assess the effects of chaya (Cnidoscolus aconitifolius) leaf and rambutan (Nephelium lappaceum L.) fruit peel pellet (CRP) supplementation on rumen fermentation, feed intake, nutrient digestibility, and nitrogen balance in crossbred beef cattle. Four beef cattle crossbred bulls (Brahman 75% × Thai native 25%), with 250 ± 15 kg of liveweight at 18 months old, were randomly selected to receive four dietary treatment groups: no supplementation (control) and the supplementation of CRP at 2, 4 and 6% of dry matter intake (DMI) by using a 4 × 4 Latin square design. The cattle were fed a concentrate at 2 kg/day, and rice straw was offered ad libitum. The results showed that rumen pH at 4 h and average post-feeding values were in the normal range, though they were slightly reduced with CRP supplementation at 4 and 6% DMI (p < 0.05). Rumen temperature, ammonia nitrogen level, and total volatile fatty acid (VFA), acetate (C2), and butyrate (C4) production were similar among treatments. Nevertheless, propionate (C3) concentration was significantly increased (p < 0.05) in the CRP groups at 2 and 4% DMI. In addition, the C2/C3 ratio and CH4 production were significantly reduced in the CRP groups, especially at 2 and 4% DMI. Rice straw intake and total feed intake in terms of %BW were significantly higher in the groups with CRP at 2 and 4% DMI (p < 0.05). The apparent nutrient digestibilities were not affected by the treatments. Nitrogen intake, nitrogen absorption, and nitrogen retention were significantly enhanced by the CRP supplementation (p < 0.05). Moreover, feces and total nitrogen excretion were not different among treatments (p > 0.05). Ultimately, the supplementation of CRP at 2 and 4% DMI significantly improved the C3 concentration, reduced the C2/C3 ratio, mitigated methane production, and enhanced feed intake and nitrogen utilization efficiency. Therefore, CRP supplementation shows promise as a rumen dietary enhancer.

Antimicrobial Peptides Controlling Resistant Bacteria in Animal Production

In the last few decades, antimicrobial resistance (AMR) has been a worldwide concern. The excessive use of antibiotics affects animal and human health. In the last few years, livestock production has used antibiotics as food supplementation. This massive use can be considered a principal factor in the accelerated development of genetic modifications in bacteria. These modifications are responsible for AMR and can be widespread to pathogenic and commensal bacteria. In addition, these antibiotic residues can be dispersed by water and sewer water systems, the contamination of soil and, water and plants, in addition, can be stocked in tissues such as muscle, milk, eggs, fat, and others. These residues can be spread to humans by the consumption of water or contaminated food. In addition, studies have demonstrated that antimicrobial resistance may be developed by vertical and horizontal gene transfer, producing a risk to public health. Hence, the World Health Organization in 2000 forbid the use of antibiotics for feed supplementation in livestock. In this context, to obtain safe food production, one of the potential substitutes for traditional antibiotics is the use of antimicrobial peptides (AMPs). In general, AMPs present anti-infective activity, and in some cases immune response. A limited number of AMP-based drugs are now available for use in animals and humans. This use is still not widespread due to a few problems like in-vivo effectiveness, stability, and high cost of production. This review will elucidate the different AMPs applications in animal diets, in an effort to generate safe food and control AMR.

Comparisons of Corn Stover Silages after Fresh- or Ripe-Corn Harvested: Effects on Digestibility and Rumen Fermentation in Growing Beef Cattle

Both waxy corn stover after fresh- (CF) and ripe-corn (CR) harvested are important byproducts of corn cropping system and have 20 d difference in harvest time. The study aimed to investigate the effects of prolonging harvest time on the nutritive value of corn stover silage by comparing CF with CR silages. In vitro ruminal experiment was firstly performed to investigate substrate degradation and fermentation of CF and CR silages. The CR diet was formulated by replacing 50% forage of CF silage with CR silage on a dry matter (DM) basis. Fourteen crossbred steers (Simmental × Limousin × local Chinese) aged 13 months with an average weight of 318.1 ± 37.1 kg were selected and randomly allocated into two dietary treatment groups. Although the CR silage had greater DM and fiber contents than CF silage, it did not alter in vitro degradation (p > 0.05), but with lower molar percentage of propionate and acetate to propionate ratio (p < 0.05). The cattle fed CR diet had a higher DM intake and lower fiber digestibility with reduction in 18S rRNA gene copies of protozoa and fungi and 16S rRNA gene copies of Fibrobacter succinogenes (p < 0.05). Further 16S rRNA gene amplicon analysis indicated a similar diversity of bacteria community between CR and CF treatments (p > 0.05). Few differences were observed in the abundance of genera larger than 1% (p > 0.05), except for the reduction in abundance of genera Ruminococcaceae_NK4A214_group in CR treatment (p < 0.05). In summary, prolonging 20 d harvest time of corn stover silage increases the forage fiber and DM content, which promotes feed intake with decreased fiber degradation, although rumen fermentation and growth performance are not changed in growing beef cattle.

China's low-emission pathways toward climate-neutral livestock production for animal-derived foods

Animal-derived food production accounts for one-third of global anthropogenic greenhouse gas (GHG) emissions. Diet followed in China is ranked as low-carbon emitting (i.e., 0.21 t CO2-eq per capita in 2018, ranking at 145th of 168 countries) due to the low average animal-derived food consumption rate, and preferential consumption of animal-derived foods with lower GHG emissions (i.e., pork and eggs versus beef and milk). However, the projected increase in GHG emissions from livestock production poses great challenges for achieving China's "carbon neutrality" pledge. We propose that the livestock sector in China may achieve "climate neutrality" with net-zero warming around 2050 by implementing healthy diet and mitigation strategies to control enteric methane emissions.

Synergistic Effects of 3-Nitrooxypropanol with Fumarate in the Regulation of Propionate Formation and Methanogenesis in Dairy Cows In Vitro

3-Nitrooxypropanol (3-NOP) is effective at reducing ruminal methane emissions in ruminants. But it also causes a drastic increase in hydrogen accumulation, resulting in feed energy waste. Fumarate is a key precursor for propionate formation and plays an important role in rumen hydrogen metabolism. Therefore, this study examined the effects of 3-NOP combined with fumarate on volatile fatty acids, methanogenesis, and microbial community structures in dairy cows in vitro. The in vitro culture experiment was performed using a 2-by-2 factorial design, two 3-NOP levels (0 or 2 mg/g dry matter [DM]) and two fumarate levels (0 or 100 mg/g DM), including 3 runs with 4 treatments, 4 replicates, and 4 blanks containing only the inoculum. Rumen fluid was collected from three lactating Holstein cows with permanent ruminal fistulas. The combination of 3-NOP and fumarate reduced methane emissions by 11.48% without affecting dry matter degradability. The propionate concentration increased and the acetate/propionate ratio decreased significantly. In terms of bacteria, the combination of 3-NOP and fumarate reduced the abundances of Ruminococcus and Lachnospiraceae_NK3A20_group and increased the abundances of Prevotella and Succiniclasticum. For archaea, the combination of 3-NOP and fumarate significantly increased the abundances of Methanobrevibacter_sp._AbM4, while the abundance of operational taxonomic unit 581 (OTU581) (belonging to an uncultured_rumen_methanogen_g__Methanobrevibacter strain) was significantly decreased. These results indicated that the combination of 3-NOP and fumarate could alleviate the accumulation of hydrogen and enhance the inhibition of methanogenesis compared with 3-NOP only in dairy cows. IMPORTANCE The global problem of climate change and the greenhouse effect has become increasingly severe, and the abatement of greenhouse gases has received great attention from the international community. Methane produced by ruminants during digestion not only aggravates the greenhouse effect but also causes a waste of feed energy. As a methane inhibitor, 3-nitrooxypropanol can effectively reduce methane emissions from ruminants. However, when it inhibits methane emissions, the emission of hydrogen increases sharply, resulting in the waste of feed resources. Fumarate is a propionic acid precursor that can promote the metabolism of hydrogen to propionic acid in animals. Therefore, we studied the effects of the combined addition of 3-nitrooxypropanol and fumarate on methanogenesis, rumen fermentation, and rumen flora. It is of great significance to inhibit methane emission from ruminants and slow down the greenhouse effect.

Effect of Feed Supplement Containing Dried Kratom Leaves on Apparent Digestibility, Rumen Fermentation, Serum Antioxidants, Hematology, and Nitrogen Balance in Goats

The objectives of the present study were to examine the influence of supplementation with dried kratom leaf (DKTL) on the performance, hematology, and nitrogen balance in goats. Four 12-month-old male crossbred (Thai Native x Anglo Nubian) goats with an initial body weight (BW) of 24.63 ± 0.95 kg were allocated randomly to receive four different levels of DKTL using a 4 × 4 Latin square design. The DKTL was added to a total mixed ration (TMR) diet with doses of 0, 2.22, 4.44, and 6.66 g/day to investigate the treatment’s efficacy. The DKTL was high in secondary metabolites, including mitragynine, total phenolics, total tannins, flavonoids, and saponins. There were quadratic effects on total DMI in terms of kg/day (p = 0.04), %BW (p = 0.05), and g/kg BW.75 (p = 0.02). DKTL increased apparent digestibility with quadratic effects (DM; p = 0.01, OM; p = 0.01, CP; p = 0.04, NDF; p = 0.01, and ADF; p = 0.01). The pH value was within the rumen’s normal pH range, whereas NH3-N and BUN concentrations were lower with DKTL supplementation, and also reduced cholesterol (CHOL, p = 0.05) and low-density lipoprotein (LDL, p = 0.01). The protozoa population decreased linearly as DKTL levels increased (p < 0.01), whereas Fibrobacter succinogenes increased quadratically at 0 h (p = 0.02), and mean values increased linearly (p < 0.01). The average value of acetic acid (C2) and methane production (CH4) decreased linearly (p < 0.05) when DKLT was added to the diet, whereas the quantity of propionic acid (C3) increased linearly (p = 0.01). Our results indicate that DKTL could be a great alternative supplement for goat feed. We believe that DKTL could provide opportunities to assist the goat meat industry in fulfilling the demands of health-conscious consumers.

Antioxidant Contents in a Mediterranean Population of Plantago lanceolata L. Exploited for Quarry Reclamation Interventions

Plantago lanceolata L. (plantain) is an interesting multipurpose perennial species whose aerial parts are used in herbal medicine due to its precious phytochemicals and are palatable to animals. Moreover, peculiar traits such as drought tolerance, an extended growth season and a deep root system, make plantain a promising pioneer plant for quarry reclamation based on the use of native species. This study evaluated the effects of different environmental conditions and seasons on the accumulation of the bioactive compounds of its aerial organs. An autochthonous plantain population was grown in three locations in Sardinia (Italy). Leaves, peduncles and inflorescences were collected between October 2020 and July 2021. Phenolic contents and antioxidant capacity were determined. The analysis of the individual phenolic compounds was performed using liquid chromatography. In leaves, the content of total phenolics, antioxidant capacity and total flavonoids were significantly influenced by location and season. Total phenolic content ranged from 65 to 240 g gallic acid equivalent kg^-1, whereas total flavonoids were from 16 to about 89 g catechin equivalent kg^-1. Neochlorogenic, chlorogenic, cryptochlorogenic acids, verbascoside, diosmin and luteolin were identified in the methanolic extracts of leaves, peduncles and inflorescences. Verbascoside was the main antioxidant isolated from plantain extracts. Results evidenced an increasing accumulation pattern of phenolics from vegetative stage to flowering, followed by a decrement towards the seed ripening as well as site-specific differences with amounts of phenolics even 25% higher for same plantain accession.

Homo-Acetogens: Their Metabolism and Competitive Relationship with Hydrogenotrophic Methanogens

Homo-acetogens are microbes that have the ability to grow on gaseous substrates such as H₂/CO₂/CO and produce acetic acid as the main product of their metabolism through a metabolic process called reductive acetogenesis. These acetogens are dispersed in nature and are found to grow in various biotopes on land, water and sediments. They are also commonly found in the gastro-intestinal track of herbivores that rely on a symbiotic relationship with microbes in order to breakdown lignocellulosic biomass to provide the animal with nutrients and energy. For this motive, the fermentation scheme that occurs in the rumen has been described equivalent to a consolidated bioprocessing fermentation for the production of bioproducts derived from livestock. This paper reviews current knowledge of homo-acetogenesis and its potential to improve efficiency in the rumen for production of bioproducts by replacing methanogens, the principal H₂-scavengers in the rumen, thus serving as a form of carbon sink by deviating the formation of methane into bioproducts. In this review, we discuss the main strategies employed by the livestock industry to achieve methanogenesis inhibition, and also explore homo-acetogenic microorganisms and evaluate the members for potential traits and characteristics that may favor competitive advantage over methanogenesis, making them prospective candidates for competing with methanogens in ruminant animals.

Dietary Coleus amboinicus Lour. decreases ruminal methanogenesis and biohydrogenation, and improves meat quality and fatty acid composition in longissimus thoracis muscle of lambs

Background

Methane production and fatty acids (FA) biohydrogenation in the rumen are two main constraints in ruminant production causing environmental burden and reducing food product quality. Rumen functions can be modulated by the biologically active compounds (BACs) of plant origins as shown in several studies e.g. reduction in methane emission, modulation of FA composition with positive impact on the ruminant products. Coleus amboinicus Lour. (CAL) contains high concentration of polyphenols that may potentially reduce methane production and modulate ruminal biohydrogenation of unsaturated FA.

This study aimed to investigate the effect of BAC of Coleus amboinicus Lour. (CAL) fed to growing lambs on ruminal methane production, biohydrogenation of unsaturated FA and meat characteristics. In this study, the in vitro experiment aiming at determining the most effective CAL dose for in vivo experiments was followed by two in vivo experiments in rumen-cannulated rams and growing lambs. Experiment 1 (RUSITEC) comprised of control and three experimental diets differing in CAL content (10%, 15%, and 20% of the total diet). The two in vivo experiments were conducted on six growing, rumen-cannulated lambs (Exp. 2) and 16 growing lambs (Exp. 3). Animals were assigned into the control (CON) and experimental (20% of CAL) groups. Several parameters were examined in vitro (pH, ammonia and VFA concentrations, protozoa, methanogens and select bacteria populations) and in vivo (methane production, digestibility, ruminal microorganism populations, meat quality, fatty acids profiles in rumen fluid and meat, transcript expression of 5 genes in meat).

Results

CAL lowered in vitro methane production by 51%. In the in vivo Exp. 3, CAL decreased methane production by 20% compared with the CON group, which corresponded to reduction of total methanogen counts by up to 28% in all experiments, notably Methanobacteriales. In Exp. 3, CAL increased or tended to increase populations of some rumen bacteria (Ruminococcus albus, Megasphaera elsdenii, Butyrivibrio proteoclasticus, and Butyrivibrio fibrisolvens). Dietary CAL suppressed the Holotricha population, but increased or tended to increase Entodiniomorpha population in vivo. An increase in the polyunsaturated fatty acid (PUFA) proportion in the rumen of lambs was noted in response to the CAL diet, which was mainly attributable to the increase in C18:3 cis-9 cis-12 cis-15 (LNA) proportion. CAL reduced the mRNA expression of four out of five genes investigated in meat (fatty acid synthase, stearoyl-CoA desaturase, lipoprotein lipase, and fatty acid desaturase 1).

Conclusions

Summarizing, polyphenols of CAL origin (20% in diet) mitigated ruminal methane production by inhibiting the methanogen communities. CAL supplementation also improved ruminal environment by modulating ruminal bacteria involved in fermentation and biohydrogenation of FA. Besides, CAL elevated the LNA concentration, which improved meat quality through increased deposition of n-3 PUFA.

• Coleus amboinicus Lour. (CAL) into sheep diet decreased CH₄ emission.

• CAL did not reduce nutrient digestibility, but inhibited the methanogen community.

• CAL increased ruminal propionate proportion and decreased acetate/propionate ratio.

• CAL elevated n-3 fatty acid concentration in ruminal fluid and meat.

• Supplementation of CAL improved some meat quality traits.

The rumen microbiome inhibits methane formation through dietary choline supplementation

Enteric fermentation from ruminants is a primary source of anthropogenic methane emission. This study aims to add another approach for methane mitigation by manipulation of the rumen microbiome. Effects of choline supplementation on methane formation were quantified in vitro using the Rumen Simulation Technique. Supplementing 200 mM of choline chloride or choline bicarbonate reduced methane emissions by 97–100% after 15 days. Associated with the reduction of methane formation, metabolomics analysis revealed high post-treatment concentrations of ethanol, which likely served as a major hydrogen sink. Metagenome sequencing showed that the methanogen community was almost entirely lost, and choline-utilizing bacteria that can produce either lactate, ethanol or formate as hydrogen sinks were enriched. The taxa most strongly associated with methane mitigation were Megasphaera elsdenii and Denitrobacterium detoxificans, both capable of consuming lactate, which is an intermediate product and hydrogen sink. Accordingly, choline metabolism promoted the capability of bacteria to utilize alternative hydrogen sinks leading to a decline of hydrogen as a substrate for methane formation. However, fermentation of fibre and total organic matter could not be fully maintained with choline supplementation, while amino acid deamination and ethanolamine catabolism produced excessive ammonia, which would reduce feed efficiency and adversely affect live animal performance.