In vitro Screening of Essential Oil Active Compounds for Manipulation of Rumen Fermentation and Methane Mitigation

Evaluation of ruminal methane and ammonia formation and microbiota composition as affected by supplements based on mixtures of tannins and essential oils using Rusitec

BACKGROUND

Dietary supplements based on tannin extracts or essential oil compounds (EOC) have been repeatedly reported as a promising feeding strategy to reduce the environmental impact of ruminant husbandry. A previous batch culture screening of various supplements identified selected mixtures with an enhanced potential to mitigate ruminal methane and ammonia formation. Among these, Q-2 (named after quebracho extract and EOC blend 2, composed of carvacrol, thymol, and eugenol) and C-10 (chestnut extract and EOC blend 10, consisting of oregano and thyme essential oils and limonene) have been investigated in detail in the present study with the semi-continuous rumen simulation technique (Rusitec) in three independent runs. For this purpose, Q-2 and C-10, dosed according to the previous study, were compared with a non-supplemented diet (negative control, NC) and with one supplemented with the commercial EOC-based Agolin® Ruminant (positive control, PC).

RESULTS

From d 5 to 10 of fermentation incubation liquid was collected and analysed for pH, ammonia, protozoa count, and gas composition. Feed residues were collected for the determination of ruminal degradability. On d 10, samples of incubation liquid were also characterised for bacterial, archaeal and fungal communities by high-throughput sequencing of 16S rRNA and 26S ribosomal large subunit gene amplicons. Regardless of the duration of the fermentation period, Q-2 and C-10 were similarly efficient as PC in mitigating either ammonia (-37% by Q-2, -34% by PC) or methane formation (-12% by C-10, -12% by PC). The PC was also responsible for lower feed degradability and bacterial and fungal richness, whereas Q-2 and C-10 effects, particularly on microbiome diversities, were limited compared to NC.

CONCLUSIONS

All additives showed the potential to mitigate methane or ammonia formation, or both, in vitro over a period of 10 d. However, several differences occurred between PC and Q-2/C-10, indicating different mechanisms of action. The pronounced defaunation caused by PC and its suggested consequences apparently determined at least part of the mitigant effects. Although the depressive effect on NDF degradability caused by Q-2 and C-10 might partially explain their mitigation properties, their mechanisms of action remain mostly to be elucidated.

Oral administration of Pinus koraiensis cone essential oil reduces rumen methane emission by altering the rumen microbial composition and functions in Korean native goat (Capra hircus coreanae)

This study aimed to investigate Pinus koraiensis cone essential oil (PEO) as a methane (CH₄) inhibitor and determine its impact on the taxonomic and functional characteristics of the rumen microbiota in goats. A total of 10 growing Korean native goats (Capra hircus coreanae, 29.9 ± 1.58 kg, male) were assigned to different dietary treatments: control (CON; basal diet without additive) and PEO (basal diet +1 g/d of PEO) by a 2 × 2 crossover design. Methane measurements were conducted every 4 consecutive days for 17-20 days using a laser CH₄ detector. Samples of rumen fluid and feces were collected during each experimental period to evaluate the biological effects and dry matter (DM) digestibility after PEO oral administration. The rumen microbiota was analyzed via 16S rRNA gene amplicon sequencing. The PEO oral administration resulted in reduced CH₄ emission (eructation CH₄/body weight^0.75, p = 0.079) without affecting DM intake; however, it lowered the total volatile fatty acids (p = 0.041), molar proportion of propionate (p = 0.075), and ammonia nitrogen (p = 0.087) in the rumen. Blood metabolites (i.e., albumin, alanine transaminase/serum glutamic pyruvate transaminase, creatinine, and triglyceride) were significantly affected (p < 0.05) by PEO oral administration. The absolute fungal abundance (p = 0.009) was reduced by PEO oral administration, whereas ciliate protozoa, total bacteria, and methanogen abundance were not affected. The composition of rumen prokaryotic microbiota was altered by PEO oral administration with lower evenness (p = 0.054) observed for the PEO group than the CON group. Moreover, PICRUSt2 analysis revealed that the metabolic pathways of prokaryotic bacteria, such as pyruvate metabolism, were enriched in the PEO group. We also identified the Rikenellaceae RC9 gut group as the taxa potentially contributing to the enriched KEGG modules for histidine biosynthesis and pyruvate oxidation in the rumen of the PEO group using the FishTaco analysis. The entire co-occurrence networks showed that more nodes and edges were detected in the PEO group. Overall, these findings provide an understanding of how PEO oral administration affects CH₄ emission and rumen prokaryotic microbiota composition and function. This study may help develop potential manipulation strategies to find new essential oils to mitigate enteric CH₄ emissions from ruminants.

Effects of Thymbra capitata essential oil on in vitro fermentation end-products and ruminal bacterial communities

An in vitro trial was carried out to investigate the effects of natural Thymbra capitata essential oil (NEO) and its main compounds [including carvacrol, p-cymene, γ-terpinene given alone or in a synthetic combination (SEO)] on ruminal fermentation and the bacterial community using batch cultures inoculated with ruminal digesta and incubating two different basal diets [high-forage (F) and high-concentrate (C) diet]. After 24 h of incubation, primary fermentation end-products [gas, methane, volatile fatty acids (VFAs) and ammonia] and rumen microbial diversity were determined. NEO reduced the total VFA concentration (P < 0.05) only in the C diet. In contrast, SEO and carvacrol decreased the total VFA concentration (P < 0.05) only in the F diet. Methane production was not affected (P > 0.05) by any of the experimental treatments or diets evaluated. Microbial diversity analysis showed only a moderate effect of carvacrol and SEO on 13 genera, including, mainly, Atopobium and Blautia (involved in subacute ruminal acidosis) or Candidatus Saccharimonas (related to laminitis). In conclusion, T. capitata EO has a limited potential to attain nutritional or environmental benefits, but further research should be carried out to clarify its effects on animal health and microbial food safety.

In vitro screening of anti-methanogenic additives for use in Australian grazing systems

Despite considerable effort to develop and optimise additives to reduce methane emissions from cattle, little information on additive effectiveness exists for cattle under grazing scenarios. As the majority of Australian cattle production occurs on grazing land it is pertinent to report on the use of additives under simulated conditions. The current study evaluated the addition of nine additives to Rhodes grass hay under in vitro conditions, to estimate their impact on methane (CH4), gas production, and rumen fermentation parameters (volatile fatty acids, rumen pH and in vitro dry matter digestibility [IVDMD]). Citral extract at 0.1% of rumen media decreased all CH4 production parameters, but reduced gas production and digestibility, compared to a 100% hay control. Similarly, Sandalwood essential oil decreased CH4 production at 48 h, IVDMD and gas production, compared to the control. Biochar + nitrates at 5 and 8% DM, and Biochar + Asparagopsis at 5% DM decreased cumulative CH4 production (15.6%, 25.9%, 23.8%, respectively; P &lt; 0.01), compared to the control. No changes in IVDMD and gas production were observed. As such, the biochar additives were considered the most promising additives from those evaluated with a substrate designed to replicate Australian grazing systems.

In Vitro Fermentation and Degradation Characteristics of Rosemary Extract in Total Mixed Ration of Lactating Dairy Cows

Rosemary extract (RE) is characterized as an antioxidant, and it has the potential to reduce methane emission and change microbial fermentation. Hence, to the extent of the evaluation of RE in ruminant nutrition, the in vitro fermentation technique was used to investigate the effects of RE on the fermentation characteristics of a total mixed ration (TMR) fed to dairy cows. Different doses of RE were added to the TMR to obtain different concentrations of antioxidants, including 0 (CON), 0.05 (LRE), and 0.10 g/kg (HRE). A total of 500 mg ground TMR was incubated in buffer solution and rumen fluid for 48 h at 39 °C. Nutrient degradability, gas production parameters, gas composition, fermentation parameters, and microbial composition were analyzed. The results showed that nutrient degradability and total volatile fatty acid concentration were not affected by the treatments. Furthermore, total methane production and proportion were depressed in a dose-dependent way. The RE increased the propionate concentration and proportion linearly and decreased the acetate concentration and proportion linearly. Finally, microbial diversity analysis showed that the richness and evenness indexes were unchanged by different treatments, while Prevotella_1 was decreased and Prevotella_7 was increased with RE supplementation. In conclusion, RE is an effective inhibitor of methane emission of microbial fermentation and changed the profile of volatile fatty acids with no disadvantageous effects on diet utilization.

Effect of a Blend of Essential Oils, Bioflavonoids and Tannins on In Vitro Methane Production and In Vivo Production Efficiency in Dairy Cows

Two trials were performed to evaluate the efficacy of a blend of essential oils, bioflavonoids and tannins on methane (CH4) emissions (in vitro) and on the production efficiency of dairy cows (in vivo). The in vitro trial tested the production of total gas and CH4 at 16, 20 and 24 h of incubation, and volatile fatty acids (VFA) at 16 and 24 h, through biochemical methane potential (BMP) assays. In the in vivo trial, milk yield, dry matter intake (DMI), feed conversion rate (FCR), milk quality and apparent total tract digestibility (aTTD) were evaluated in 140 lactating Holstein Friesian cows. Animals were allocated into two groups: (i) Control, standard diet; (ii) Treatment, standard diet plus 10 g/head/d of a powder with a 10% concentration of a blend of essential oils, bioflavonoids and tannins. Statistical analysis was performed using the mixed procedure of SAS either for single or repeated measures. For all the parameters a p-value ≤ 0.05 was considered statistically significant. The blend significantly reduced the in vitro total gas and CH4 emissions at 16, 20 and 24 h of incubation (p < 0.001). In addition, acetic acid was reduced (p < 0.001), while propionic acid concentration was increased (p < 0.001) at 16 h and 24 h. In the in vivo trial, the Treatment group showed significantly raised milk yield, DMI, FCR (p < 0.001), and of the aTTD of cellulose and starch (p ≤ 0.002), while the milk quality traits were not affected. Overall, the results from the study indicated that the blend of essential oils, bioflavonoids, and tannins significantly reduced in vitro total gas and CH4 production and improved the production efficiency of lactating dairy cows in vivo.

Harnessing plant bioactivity for enteric methane mitigation in Australia

This review provides examples of the utilisation of plant bioactivity to mitigate enteric methane (CH4) emissions from the Australian ruminant production systems. Potential plant-based mitigation strategies that reduce CH4 without major impacts on forage digestibility include the following: (i) low methanogenic tropical and temperate grass, legume and shrub forage species, which offer renewable and sustainable solutions and are easy to adopt, but may have restricted geographical distribution or relatively high costs of establishment and maintenance; (ii) plant-based agricultural by-products including grape marc, olive leaves and fruit, and distiller’s grains that can mitigate CH4 and provide relatively cheap high-nutrient supplements, while offsetting the impact of agricultural waste, but their use may be limited due to unfavourable characteristics such as high protein and water content or cost of transport; (iii) plant extracts, essential oils and pure compounds that are abundant in Australian flora and offer exciting opportunities on the basis of in vitro findings, but require verification in ruminant production systems. The greatest CH4 mitigation potential based on in vitro assays come from the Australian shrubs Eremophila species, Jasminum didymium and Lotus australis (>80% CH4 reduction), tropical forages Desmanthus leptophyllus, Hetropogon contortus and Leucaena leucocephala (~40% CH4 reduction), temperate forages Biserrula pelecinus (70–90% CH4 reduction), perennial ryegrass and white clover (~20% CH4 reduction), and plant extracts or essential oils from Melaleuca ericifolia, B. pelecinus and Leptospermum petersonii (up to 80% CH4 reduction). Further research is required to confirm effectiveness of these plant-based strategies in vivo, determine optimal doses, practical modes of delivery to livestock, analyse benefit–cost ratios and develop pathways to adoption.

Interactions among Natural Active Ingredients to Improve the Efficiency of Rumen Fermentation In Vitro

Twelve essential oils (EO): Anise star, cassia, geraniol, lemongrass (LEM), limonene, thyme, tea tree, coriander (COR), capsicum, black pepper, turmeric and ginger (GIN), in Experiment 1 at three doses; and different combinations of LEM, COR and GIN oils in Experiment 2, were evaluated in in vitro batch microbial fermentation using ruminal fluid from four dairy cows fed a 50:50 forage: concentrate diet. In experiment 1, LEM tended to increase the propionate proportion and tended to decrease the acetate to propionate ratio. Anise star, COR, and thyme tended to increase butyrate proportion. Capsicum, COR, and thyme decreased ammonia-N concentration. In experiment 2, a synergy was observed between LEM and COR that resulted in an increase in total volatile fatty acids and propionate proportion, and a decrease in the acetate to propionate ratio. However, the addition of high doses of GIN to the mix had an antagonistic effect on the rumen fermentation profile of the LEM + COR mix. Careful selection and combination of these EO may result in useful mixtures with synergistic interactions to modulate rumen microbial fermentation profile.

Evaluation of dietary addition of 2 essential oils from Achillea moschata, or their components (bornyl acetate, camphor, and eucalyptol) on in vitro ruminal fermentation and microbial community composition

This study investigated the effects of 2 Achillea moschata essential oils extracted from plants collected in 2 different valleys of the Italian Alps and 3 pure compounds of oils - bornyl acetate (BOR), camphor (CAM), and eucalyptol (EUCA) - on in vitro ruminal fermentation and microbiota. An in vitro batch fermentation experiment (Exp. 1) tested the addition of all of the substances (2 essential oils and 3 compounds) in fermentation bottles (120 mL) at 48 h of incubation, whereas a subsequent in vitro continuous culture experiment (Exp. 2) evaluated the pure compounds added to the fermenters (2 L) for a longer incubation period (9 d). In both experiments, total mixed rations were incubated with the additives, and samples without additives were included as the control (CTR). Each treatment was tested in duplicate and was repeated in 3 and 2 fermentation runs in Exp. 1 and 2, respectively. Gas production (GP) in Exp. 1 was similar for all of the treatments, and short chain volatile fatty acid (SCFA) production was similar in both experiments except for a decrease of SCFA produced (P = 0.029) due to EUCA addition in Exp. 2. Compared to CTR, BOR and CAM reduced the valerate proportion (P = 0.04) in Exp. 1, and increased (P < 0.01) the acetate proportion in Exp. 2. All treatments increased (P < 0.01) total protozoa counts (+36.7% and +48.4% compared to CTR on average for Exp. 1 and 2, respectively). In Exp. 1, all of the treatments lowered the Bacteroidetes and Firmicutes and increased the Proteobacteria relative abundances (P < 0.05), whereas in Exp. 2, the EUCA addition increased (P = 0.012) the Ruminococcus. In Exp. 1, methane (CH4) as a proportion of the GP was lowered (P = 0.004) by the addition of CAM and EUCA compared to CTR, whereas in Exp. 2, EUCA reduced the amount of stoichiometrically calculated CH4 compared to CTR. Overall, essential oils extracted from A. moschata and the pure compounds did not depress in vitro rumen fermentation, except for EUCA in Exp. 2. In both experiments, an increase of the protozoal population occurred for all the additives.

Effects of Three Herbs on Methane Emissions from Beef Cattle

Simple Summary

Cattle represent a significant source of greenhouse gases (GHGs). In 2010, cattle emitted 5.0 gigatons of CO₂ equivalents globally, which represents about 62% of the livestock sector emissions. Therefore, mitigating GHGs such as methane (CH₄) originating from the cattle industry, offers an opportunity to reduce GHG emissions and climate change over the short term. Ruminant nutritionists have developed different strategies, which include the use of antibiotics, herbs and chemical compounds, such as nitrate, to manipulate rumen fermentation and reduce CH₄ emissions. So, the objectives of the present work were to evaluate the in vivo antimethanogenic effects of three herbs: Cymbopogon citratus (CC), Matricaria chamomilla (MC) and Cosmos bipinnatus (CB) on beef cattle fed a high in concentrate diet and the effects of increasing levels of CC on enteric CH₄ emissions by beef cattle fed a ration low in concentrate. We concluded that CC significantly reduced methane yield (g of CH₄/kg of DMI) by 33%, CB reduced methane yield by 28%, and MC had no significant effect. In Experiment 2, CC supplemented with 2% of the daily DMI significantly reduced the total daily CH₄ emissions by 26% without affecting the supply of nutrients to the animal.

Abstract

The objectives of the present work were to evaluate the in vivo antimethanogenic effects of Cymbopogon citratus (CC), Matricaria chamomilla (MC) and Cosmos bipinnatus (CB) on beef cattle fed a high in concentrate diet (forage-to-concentrate ratio [F:C] of 19.4:80.6), and the effects of increasing levels of CC (0%, 2%, 3%, and 4% of the daily DM intake (DMI)) on enteric CH₄ emissions by beef cattle fed a ration low in concentrate (F:C ratio of 49.3:50.7). Two experiments were conducted to address the objectives. For the first experiment, eight Charolais × Brown Swiss steers distributed in a replicated 4 × 4 Latin square experimental design were used. Four treatments were evaluated: (1) control diet (CO), (2) CO + 365 g dry matter (DM)/d CB, (3) CO + 365 g DM/d MC, (4) CO + 100 g DM/d CC. For Experiment 2, four Charolais x Brown Swiss steers distributed in a single 4 × 4 Latin square design were used. It was concluded that 100 g DM per day CC and 365 g DM per day CB (Experiment 1) reduced CH₄ yield of beef cattle. In Experiment 2, CC supplementation levels exceeding 2% of DMI reduced daily CH₄ emissions but at the expense of decreasing digestibility of DM.

Effects of Replacing Extruded Maize by Dried Citrus Pulp in a Mixed Diet on Ruminal Fermentation, Methane Production, and Microbial Populations in Rusitec Fermenters

Citrus pulp is a highly abundant by-product of the citrus industry. The aim of this study was to assess the effects of replacing extruded maize (EM; 20% of total diet) by dried citrus pulp (DCP; 20%) in a mixed diet on rumen fermentation and microbial populations in Rusitec fermenters. The two diets contained 50% alfalfa hay and 50% concentrate, and the same protein level. Four Rusitec fermenters were used in a cross-over design with two 13-d incubation runs. After 7-d of diet adaptation, diet disappearance, fermentation parameters, microbial growth, and microbial populations were assessed. Fermenters receiving the DCP showed greater pH values and fiber disappearance (p < 0.001) and lower methane production (p = 0.03) than those fed EM. Replacing EM by DCP caused an increase in the proportions of propionate and butyrate (p < 0.001) and a decrease in acetate (p = 0.04). Microbial growth, bacterial diversity, and the quantity of bacteria and protozoa DNA were not affected by the diet, but the relative abundances of fungi and archaea were greater (p < 0.03) in solid and liquid phases of DCP fermenters, respectively. Results indicate that DCP can substitute EM, promoting a more efficient ruminal fermentation.

The Reduction of Methane Production in the In Vitro Ruminal Fermentation of Different Substrates is Linked with the Chemical Composition of the Essential Oil

Simple Summary

There is growing concern about how animal-derived foods are produced. Methane production in ruminants has received much attention in relation to its contribution to greenhouse gases and its effect on global warming. Another aspect of livestock production that is questioned by consumers is related to in-feed antibiotics added to improve feed efficiency, and due to health safety issues, their use has been banned or under revision in some parts of the world. Hence, there is the need to find new solutions to mitigate methane production in the rumen in a way that is considered safe and environmental-friendly by consumers and feasible, and without a negative impact on the farmers. Among the alternatives, the use of essential oils to modify rumen fermentation has attracted attention. This paper explores the effectiveness of essential oils obtained from two plants, Lippia turbinata and Tagetes minuta, to reduce methane production during the in vitro fermentation of substrates that are representative of different livestock production systems. The main conclusion to which we arrived is that the extent of the reduction in methane production depends on the interaction between the fermentation conditions that are generated by different substrates and the chemical profile of the essential oil, especially regarding its proportion of oxygenated compounds.

Abstract

There is interest in identifying natural products capable of manipulating rumen microbial activity to develop new feed additives for ruminant nutrition as a strategy to reduce methane. Two trials were performed using the in vitro gas production technique to evaluate the interaction of substrate (n = 5) and additive (n = 6, increasing doses: 0, 0.3, 3, 30, and 300 µL/L of essential oils—EO—of Lippia turbinata or Tagetes minuta, and monensin at 1.87 mg/L). The two EO utilized were selected because they differ markedly in their chemical composition, especially in the proportion of oxygenated compounds. For both EO, the interaction between the substrate and additive was significant for all variables; however, the interaction behaved differently for the two EO. Within each substrate, the response was dose-dependent, without effects at a low level of EO and a negative outcome at the highest dose. The intermediate dose (30 µL/L) inhibited methane with a slight reduction on substrate digestibility, with L. turbinata being more effective than T. minuta. It is concluded that the effectiveness of the EO to reduce methane production depends on interactions between the substrate that is fermented and the additive dose that generates different characteristics within the incubation medium (e.g., pH); and thus, the chemical nature of the compounds of the EO modulates the magnitude of this response.

Effects of oregano essential oil on in vitro ruminal fermentation, methane production, and ruminal microbial community

Different inclusion rates of oregano essential oil (OEO) were investigated for their effects on ruminal in vitro fermentation parameters, total gas, methane production, and bacterial communities. Treatments were (1) control, 0 mg/L of OEO (CON); 13 mg/L (OEO1); 52 mg/L (OEO2); 91 mg/L (OEO3); and 130 mg/L (OEO4), each incubated with 150 mL of buffered rumen fluid and 1,200 mg of substrate for 24 h using the Ankom in vitro gas production system (Ankom Technology Corp., Fairport, NY). Treatment responses were statistically analyzed using polynomial contrasts. Digestibility of DM, NDF, and ADF increased quadratically with increasing OEO inclusion rates. Digestibility of DM and NDF were highest for OEO2, whereas ADF digestibility was highest for OEO3, compared with CON, with the remaining treatments being intermediate and similar. Ammonia nitrogen concentrations decreased from CON at a quadratic rate with increasing OEO inclusion rates, and OEO2 had the lowest concentration compared with the other groups. Total VFA, acetate, propionate, butyrate, valerate, and isovalerate concentrations linearly decreased with increasing OEO inclusion rates. Total gas production levels by CON and OEO4 were greater than those of OEO1, OEO2, and OEO3 in a quadratic response, and methane production linearly decreased from CON, compared with OEO4, at a decreasing rate with OEO inclusion rates. As determined by 16S rRNA sequencing, the α biodiversity of ruminal bacteria was similar among OEO inclusion rates. Increasing OEO inclusion rates linearly increased the relative abundance of Prevotella and Dialister bacteria. Several bacteria demonstrated different polynomial responses, whereas several bacteria were similar among increasing OEO inclusion rates. These results suggested that OEO supplementation can modify ruminal fermentation to alter VFA concentrations and reduce methane emissions by extensively altering the ruminal bacterial community, suggesting an optimal feeding rate for future animal studies of approximately 52 mg/L for mature ruminants.

Volatiles and Tannins in Pistacia lentiscus and Their Role in Browsing Behavior of Goats (Capra hircus)

Goat herding is an important tool in the ecologically sound management of Mediterranean shrublands and woodlands, although effective levels of woody biomass removal by the goats is neither guaranteed nor easy to predict. Preliminary observations indicated that one reason for this may be poor understanding of plant-herbivore interactions that operate intraspecifically at the local spatial scale. We asked, whether goats show intraspecific preferences among neighboring plants when foraging a small local population of Pistacia lentiscus, a dominant tall shrub. First, we characterized and quantified the profile of stored and emitted volatile organic compounds (VOCs) and the PEG-binding capacity of tannins (a proxy for protein binding capacity) in the foliage of P. lentiscus shrubs, sampled within an area of 0.9 ha. We then tested goat preference between pairs of these shrubs that differed in chemical composition. Almost all sampled P. lentiscus shrubs were allocated to one of two distinct VOC chemotypes: one dominated by germacrene D and limonene (designated chemotype L) and the other by germacrene D and α-pinene (chemotype P). In contrast, continuous moderate variability was found in the binding capacity of tannins in the foliage. Goats showed preference for shrubs of chemotype L over those of chemotype P, and their preference was negatively correlated with the binding capacity of tannins. Possible influences of VOCs on goat preference that may explain the observed patterns are discussed in the light of possible context-dependent interpretation of plant VOC signals by large mammalian herbivores.

Essential oils from Lippia turbinata and Tagetes minuta persistently reduce in vitro ruminal methane production in a continuous-culture system

The aim of the present study was to evaluate the impact of essential oils (EO) from Lippia turbinata (LT) and Tagetes minuta (TM) as well as the rotation of both EO on fermentation parameters in vitro. Daily addition of LT, TM, or a 3-day rotation between them (TM/LT), as well as a control (without EO), was evaluated using the rumen simulation technique (Rusitec). The experiment lasted 19 days, with a 7-day adaptation period, followed by 12 days of treatment (Days 0–12). The EO were dissolved in ethanol (70% vol/vol) to be added daily to fermenters (300 μL/L) from Day 0. Daily measurements included methane concentration, total gas production, apparent DM disappearance and pH, which started 2 days before the addition of treatments. On Days 0, 4, 8 and 12 apparent crude protein disappearance and neutral detergent fibre disappearance, ammonia and volatile fatty acid concentration and composition were determined. Methane production was significantly inhibited shortly after addition of both EO added individually, and persisted over time with no apparent adaptation to EO addition. The TM/LT treatment showed a similar effect on methane production, suggesting that rotating the EO did not bring further improvements in reduction or persistency compared with the inclusion of the EO individually. Gas production, total volatile fatty acid concentration and composition and apparent crude protein disappearance were not affected by EO addition. Compared with the control, a 5% reduction of apparent DM disappearance and a 15% reduction of neutral detergent fibre disappearance were observed with the addition of EO. Only TM and TM/LT reduced ammonia concentration. Given the significant and persistent antimethanogenic activity of both EO, and the potential of T. minuta to modify nitrogen metabolism, EO from these plant species are of interest for developing new feed additives with potential application in ruminant nutrition that are also likely to be acceptable to consumers.

Effects of pure plant secondary metabolites on methane production, rumen fermentation and rumen bacteria populations in vitro

In this study, the effects of seven pure plant secondary metabolites (PSMs) on rumen fermentation, methane (CH₄ ) production and rumen bacterial community composition were determined. Two in vitro trials were conducted. In trial 1, nine concentrations of 8-hydroxyquinoline, α-terpineol, camphor, bornyl acetate, α-pinene, thymoquinone and thymol were incubated on separate days using in vitro 24-hr batch incubations. All compounds tested demonstrated the ability to alter rumen fermentation parameters and decrease CH₄ production. However, effective concentrations differed among individual PSMs. The lowest concentrations that reduced (p < .05) CH₄ production were as follows: 8 mg/L of 8-hydroxyquinoline, 120 mg/L of thymoquinone, 240 mg/L of thymol and 480 mg/L of α-terpineol, camphor, bornyl acetate and α-pinene. These concentrations were selected for use in trial 2. In trial 2, PSMs were incubated in one run. Methane was decreased (p < .05) by all PSMs at selected concentrations. However, only 8-hydroxyquinoline, bornyl acetate and thymoquinone decreased (p < .05) CH₄ relative to volatile fatty acids (VFAs). Based on denaturing gradient gel electrophoresis analysis, different PSMs changed the composition of bacterial communities to different extents. As revealed by Ion Torrent sequencing, the effects of PSMs on relative abundance were most pronounced in the predominant families, especially in Lachnospiraceae, Succinivibrionaceae, Prevotellaceae, unclassified Clostridiales and Ruminococcaceae. The CH₄ production was correlated negatively (-.72; p < .05) with relative abundance of Succinivibrionaceae and positively with relative abundance of Ruminococcaceae (.86; p < .05). In summary, this study identified three pure PSMs (8hydroxyquinoline, bornyl acetate and thymoquinone) with potentially promising effects on rumen CH₄ production. The PSMs tested in this study demonstrated considerable impact on rumen bacterial communities even at the lowest concentrations that decreased CH₄ production. The findings from this study may help to elucidate how PSMs affect rumen bacterial fermentation.