Invited review: Essential oils as modifiers of rumen microbial fermentation

Chemical composition, and antioxidant and antimicrobial activities of essential Oil of Phyllostachys heterocycla cv. Pubescens varieties from China

The essential oils of Phyllostachys heterocycla cv. Pubescens, Phyllostachys heterocycla cv. Gracilis, Phyllostachys heterocycla cv. Heterocycla and Phyllostachys kwangsiensis leaves were obtained by steam distillation. Their chemical components were separated and identified by gas chromatography/mass spectrometry (GC/MS). Meanwhile, the effect of scavenging free radicals of essential oil was assayed by using the DPPH·method with Trolox^® as control to evaluate their antioxidant capacities. Gram-positive (Staphyloccocus aureus) and Gram-negative (Escherichia coli) were selected as the indicator microorganisms to evaluate the antimicrobial activity. Antimicrobial properties were estimated by the agar diffusion method. The results show that 63 components were separated and identified by GC/MS from these varieties of bamboo leaves. cis-3-Hexenol, whose content in cv. Pubescens, Gracilis, Heterocycla and Ph. kwangsiensis was 27.11%, 24.62%, 30.51% and 34.65%, respectively, was the main constituent. The relative content of alcohol compounds in these varieties of essential oils ranged from 39.8% to 46.64%. All of the bamboo leaf essential oils possessed certain antioxidant capacity; the corresponding IC₅₀ values were 3.1622, 4.9353, 4.2473, and 5.4746 μL/mL, respectively. Essential oils of all tested bamboo spp. were active against Staphylococcus epidermidis and E. coli, showing a positive correlation with the essential oil concentration of 50.42-300 μL/mL. The results indicated there were no significant differences among three varieties and the related species with respect to their antioxidant and antimicrobial activities. This paper provides evidence for studying the essential composition from different varieties of bamboo leaves.

In vitro evaluation of cashew nut shell liquid as a methane-inhibiting and propionate-enhancing agent for ruminants

Cashew nut shell liquid (CNSL) containing antibacterial phenolic compounds was evaluated for its potency as a feed additive for ruminants. In experiment 1, ruminal responses to CNSL supplementation were assessed using a batch culture system. Rumen fluid from cattle was diluted with artificial saliva and incubated for 18h in a batch culture with a mixed diet containing a 30:70 hay:concentrate diet to which raw or heated CNSL was added at a final concentration of 500 μg/mL. In experiment 2, a Rusitec, using rumen fluid from the same cattle, was operated over a period of 7 d during which only raw CNSL was tested at concentrations of 0, 50, 100, or 200 μg/mL, and variations in fermentation and bacterial population were assessed. In experiment 3, a pure culture study was conducted using selected bacteria to determine their susceptibility to CNSL. In experiment 1, methane production was inhibited by raw CNSL (56.9% inhibition) but not by heated CNSL. Total volatile fatty acid concentration was not affected, whereas increased concentrations of propionate and decreased concentrations of acetate and butyrate were observed using either raw or heated CNSL. These changes were more obvious when raw CNSL was tested. In experiment 2, raw CNSL inhibited methanogenesis and increased propionate production in a dose-dependent manner, showing maximum methane inhibition (70.1%) and propionate enhancement (44.4%) at 200 μg/mL supplementation. Raw CNSL increased total volatile fatty acid concentration and dry matter digestibility. Raw CNSL also appeared to induce a dramatic shift in the population of rumen microbiota, based on decreased protozoa numbers and changes in quantitative PCR assay values for representative bacterial species. In experiment 3, using pure cultures, raw CNSL prevented the growth of hydrogen-, formate-, and butyrate-producing rumen bacteria, but not the growth of bacteria involved in propionate production. Based on these data, raw CNSL, rich in the antibacterial phenolic compound anacardic acid, is a potential candidate feed additive with selective activity against rumen microbes, leading to fermentation that results in decreased methane and enhanced propionate production.

Mitigation of greenhouse gas emissions in the production of fluid milk

Global climate change, driven by the buildup of greenhouse gas (GHG) emissions in the atmosphere, is challenging the dairy industries in the United States and throughout the world to develop sustainable initiatives to reduce their environmental impact. The U.S. dairy industry has committed to lowering the GHG emissions, primarily CH(4), N(2)O, and CO(2), in each sector of the fluid milk supply chain which extends from the farm, to the processing plant, and to distribution of the packaged product, where it is refrigerated by the retailer and then the consumer. This chapter provides an overview of the life cycle analysis (LCA) technique and its use in identifying the GHG emissions in each sector of the fluid milk supply chain, from cradle to grave, and the best practices and research that is currently being conducted to reduce or mitigate GHG emissions in each sector. We also discuss the use of on-farm and off-farm process simulation as tools for evaluating on-farm mitigation techniques, off-farm alternative processing scenarios, and use of alternative energy management practices.

Measurement and prediction of enteric methane emission

The greenhouse gas (GHG) emissions from the agricultural sector account for about 25.5% of total global anthropogenic emission. While CO(2) receives the most attention as a factor relative to global warming, CH(4), N(2)O and chlorofluorocarbons (CFCs) also cause significant radiative forcing. With the relative global warming potential of 25 compared with CO(2), CH(4) is one of the most important GHGs. This article reviews the prediction models, estimation methodology and strategies for reducing enteric CH(4) emissions. Emission of CH(4) in ruminants differs among developed and developing countries, depending on factors like animal species, breed, pH of rumen fluid, ratio of acetate:propionate, methanogen population, composition of diet and amount of concentrate fed. Among the ruminant animals, cattle contribute the most towards the greenhouse effect through methane emission followed by sheep, goats and buffalos, respectively. The estimated CH(4) emission rate per cattle, buffaloe, sheep and goat in developed countries are 150.7, 137, 21.9 and 13.7 (g/animal/day) respectively. However, the estimated rates in developing countries are significantly lower at 95.9 and 13.7 (g/animal/day) per cattle and sheep, respectively. There exists a strong interest in developing new and improving the existing CH(4) prediction models to identify mitigation strategies for reducing the overall CH(4) emissions. A synthesis of the available literature suggests that the mechanistic models are superior to empirical models in accurately predicting the CH(4) emission from dairy farms. The latest development in prediction model is the integrated farm system model which is a process-based whole-farm simulation technique. Several techniques are used to quantify enteric CH(4) emissions starting from whole animal chambers to sulfur hexafluoride (SF6) tracer techniques. The latest technology developed to estimate CH(4) more accurately is the micrometeorological mass difference technique. Because the conditions under which animals are managed vary greatly by country, CH(4) emissions reduction strategies must be tailored to country-specific circumstances. Strategies that are cost effective, improve productivity, and have limited potential negative effects on livestock production hold a greater chance of being adopted by producers. It is also important to evaluate CH(4) mitigation strategies in terms of the total GHG budget and to consider the economics of various strategies. Although reductions in GHG emissions from livestock industries are seen as high priorities, strategies for reducing emissions should not reduce the economic viability of enterprises.

Methanogens: methane producers of the rumen and mitigation strategies

Methanogens are the only known microorganisms capable of methane production, making them of interest when investigating methane abatement strategies. A number of experiments have been conducted to study the methanogen population in the rumen of cattle and sheep, as well as the relationship that methanogens have with other microorganisms. The rumen methanogen species differ depending on diet and geographical location of the host, as does methanogenesis, which can be reduced by modifying dietary composition, or by supplementation of monensin, lipids, organic acids, or plant compounds within the diet. Other methane abatement strategies that have been investigated are defaunation and vaccines. These mitigation methods target the methanogen population of the rumen directly or indirectly, resulting in varying degrees of efficacy. This paper describes the methanogens identified in the rumens of cattle and sheep, as well as a number of methane mitigation strategies that have been effective in vivo.

Chemical composition and antibacterial potential of Artemisia arborescens L. essential oil

This study was undertaken to characterize the essential oil (EO) of Artemisia arborescens growing wild in Sicily. EO, extracted by steam distillation, was examined for its chemical composition and for its capability to inhibit some food-borne pathogen bacteria. A total of 43 compounds (13 monoterpene hydrocarbons, 14 oxygenated monoterpenes, 10 sesquiterpene hydrocarbons, three oxygenated sesquiterpenes and less amount of other three compounds), which account 93.73% of the total oil, were identified by gas chromatography and gas chromatography-mass spectrometry. Oxygenated monoterpenes (57.32%) constituted the main fraction, with β-thujone as the main compound (45.04%), followed by the sesquiterpene hydrocarbon chamazulene (22.71%). Undiluted EO showed a large inhibition spectrum against strains of Listeria monocytogenes (34 out of 44), whilst it was ineffective against enterobacteria and salmonellas. The minimum inhibition concentration (MIC) was evaluated for the two most sensitive strains (L. monocytogenes 186 and 7BO) at two cellular concentrations (10(6) and 10(7) CFU ml(-1)). The lowest MIC (0.625 μl ml(-1), dilution of oil with acetone) was found for strain L. monocytogenes 186 at 10(6) CFU ml(-1).

Decrease of ruminal methane production in Rusitec fermenters through the addition of plant material from rhubarb (Rheum spp.) and alder buckthorn (Frangula alnus)

Roots of rhubarb (Rheum spp.) and bark of alder buckthorn (Frangula alnus) were tested as feed additives for decreasing ruminal methane production released from anaerobic fermentation of a forage-based diet in a rumen-simulating fermenter (Rusitec). Sixteen fermentation units (vessels) were set up for the experiment lasting 19 d. Treated vessels were supplied with 1g/d of rhubarb or alder buckthorn (4 vessels per plant species); another 4 vessels received 12 microM sodium monensin (positive control), and the remaining 4 vessels were controls (no additive). Upon termination of the experimental period, batch cultures were inoculated with the liquid contents of the vessels for examining in vitro fermentation kinetics of cellulose, starch, barley straw, and the same substrate used in the Rusitec cultures. Monensin induced changes in fermentation in agreement with those reported in the literature, and inocula from those cultures decreased the fermentation rate and total gas produced in the gas kinetics study. Rhubarb decreased methane production, associated with limited changes in the profile of volatile fatty acids throughout the duration of the study, whereas digestibility and total volatile fatty acids production were not affected. Rhubarb inocula did not affect gas production kinetics except for cellulose. Alder buckthorn decreased only methane concentration in fermentation gas, and this effect was not always significant. The use of rhubarb (milled rhizomes of Rheum spp.) in the diets of ruminants may effectively modulate ruminal fermentation by abating methane production, thus potentially involving productive and environmental benefits.

A new perspective on the use of plant secondary metabolites to inhibit methanogenesis in the rumen

Recently, greenhouse gas emissions have been of great concern globally. Ruminant livestock due to production of methane during normal fermentation in the rumen contributes substantially to the greenhouse effects. During the recent decade, a paradigm shift has been initiated whether plant secondary metabolites (PSM) could be exploited as natural safe feed additives alternative to chemical additives to inhibit enteric methanogenesis. More than 200,000 defined structures of PSM have been known. Some plants or their extracts with high concentrations of bioactive PSM such as saponins, tannins, essential oils, organosulphur compounds, flavonoids and many other metabolites appear to have potential to inhibit methane production in the rumen. The possible mechanisms and effects of many PSM on rumen methanogenesis are not clearly understood. Saponins may decrease methanogenesis through the inhibition of rumen protozoa and in turn may suppress the numbers and activity of methanogens. Although the direct effect of saponins on methanogens has not been demonstrated, saponins might inhibit methanogens at high doses. Tannins may inhibit the methanogenesis directly and also via inhibition of protozoal growth. Essential oils, organosulphur compounds and flavonoids appear to have direct effects against methanogens, and a reduction of protozoa associated methanogenesis probably plays a minor role for these metabolites. The chemical structure and molecular weight of the PSM and chemical composition of diets dependent upon the different feeding regimes may influence the effects of PSM on methane production. Although PSM may negatively affect nutrient utilization, there is evidence that methanogenesis could be suppressed without adversely affecting rumen fermentation, which could be exploited to mitigate methane emission in ruminants.

Evaluation of In Vitro Activity of Essential Oils against Trypanosoma brucei brucei and Trypanosoma evansi

Essential oils (EOs) from Cymbopogon citratus (CC), Eucalyptus citriodora (EC), Eucalyptus camaldulensis (ED), and Citrus sinensis (CS) were obtained by hydrodistillation process. The EOs were evaluated in vitro for activity against Trypanosoma brucei brucei (Tbb) and Trypanosoma evansi (T. evansi). The EOs were found to possess antitrypanosomal activity in vitro in a dose-dependent pattern in a short period of time. The drop in number of parasite over time was achieved doses of 0.4 g/ml, 0.2 g/mL, and 0.1 g/mL for all the EOs. The concentration of 0.4 g/mL CC was more potent at 3 minutes and 2 minutes for Tbb and T. evansi, respectively. The GC-MS analysis of the EOs revealed presence of Cyclobutane (96.09%) in CS, 6-octenal (77.11%) in EC, Eucalyptol (75%) in ED, and Citral (38.32%) in CC among several other organic compounds. The results are discussed in relation to trypanosome chemotherapy.

Strategies to reduce methane emissions from farmed ruminants grazing on pasture

Methane emissions from livestock are a significant contributor to greenhouse gas emissions and have become a focus of research activities, especially in countries where agriculture is a major economic sector. Understanding the complexity of the rumen microbiota, including methane-producing Archaea, is in its infancy. There are currently no robust, reproducible and economically viable methods for reducing methane emissions from ruminants grazing on pasture and novel innovative strategies to diminish methane output from livestock are required. In this review, current approaches towards mitigation of methane in pastoral farming are summarised. Research strategies based on vaccination, enzyme inhibitors, phage, homoacetogens, defaunation, feed supplements, and animal selection are reviewed. Many approaches are currently being investigated, and it is likely that more than one strategy will be required to enable pastoral farming to lower its emissions of methane significantly. Different strategies may be suitable for different farming practices and systems.

Dietary phytochemicals as rumen modifiers: a review of the effects on microbial populations

In the recent years, the exploration of bioactive phytochemicals as natural feed additives has been of great interest among nutritionists and rumen microbiologists to modify the rumen fermentation favorably such as defaunation, inhibition of methanogenesis, improvement in protein metabolism, and increasing conjugated linoleic acid content in ruminant derived foods. Many phytochemicals such as saponins, essential oils, tannins and flavonoids from a wide range of plants have been identified, which have potential values for rumen manipulation and enhancing animal productivity as alternatives to chemical feed additives. However, their effectiveness in ruminant production has not been proved to be consistent and conclusive. This review discusses the effects of phytochemicals such as saponins, tannins and essential oils on the rumen microbial populations, i.e., bacteria, protozoa, fungi and archaea with highlighting molecular diversity of microbial community in the rumen. There are contrasting reports of the effects of these phytoadditives on the rumen fermentation and rumen microbes probably depending upon the interactions among the chemical structures and levels of phytochemicals used, nutrient composition of diets and microbial components in the rumen. The study of chemical structure-activity relationships is required to exploit the phytochemicals for obtaining target responses without adversely affecting beneficial microbial populations. A greater understanding of the modulatory effects of phytochemicals on the rumen microbial populations together with fermentation will allow a better management of the rumen ecosystem and a practical application of this feed additive technology in livestock production.

Effect of a mixture of supplemental dietary plant essential oils on performance of periparturient and early lactation dairy cows

Plant essential plant oils (EO) are volatile aromatic compounds with antimicrobial activity that can alter ruminal fermentation when used as dietary supplements. A feeding trial was conducted to determine the effects of dietary supplementation of periparturient and early lactation dairy cows with a specific mixture of EO. Forty multiparous Holstein cows were randomly assigned to either control (C) or EO-supplemented (1.2 g/cow per day) total mixed rations (TMR). Feeding of treatment diets commenced 3 wk before the expected calving date and continued through 15 wk in lactation. The prepartum TMR contained 70% forage [70% corn silage, 15% alfalfa silage, and 15% wheat straw; dry matter (DM) basis]. The lactation TMR contained 50% forage (60% corn silage, 33% alfalfa silage, 7% alfalfa hay; DM basis). Prepartum and lactation TMR were formulated to contain 12 and 17% CP (DM basis), respectively. There were no differences between treatments for prepartum DM intake (DMI), but DMI was 1.8 kg/d less for EO than C on average across the 15-wk lactation trial. Plasma concentrations of glucose, nonesterified fatty acids, beta-hydroxybutyrate, and urea-N on samples collected -21, -14, -7, -1, 1, 8, 15, 22, and 29 d relative to calving were unaffected by treatment. There were no differences between treatments for actual or fat-corrected milk yields on average across the 15-wk lactation trial. Milk protein content was 0.15% units less for EO than C. Feed efficiency (kg of milk per kg of DMI) tended to be greater for EO than C on average and was greater during wk 8 to 14 of lactation. Prepartum and lactation body weight and condition score measurements were unaffected by treatment. There was no benefit to EO in prepartum dairy cows. Dietary supplementation with EO reduced DMI in early lactation dairy cows with no effect on milk yield.

A blend of essential plant oils used as an additive to alter silage fermentation or used as a feed additive for lactating dairy cows

A blend of essential plant oils was evaluated for its effects on silage fermentation and animal performance. In the first experiment, the blend of essential oils was mixed with freshly chopped whole-plant corn to achieve a concentration of 0, 40, or 80 mg of active product per kilogram of fresh forage weight. Whole-plant corn was also mixed with a buffered propionic acid-based product at 0.2% of fresh forage weight. The blend of essential oils did not affect the populations of yeasts, molds, lactic acid bacteria, or enterobacteria; the fermentation end products; or the aerobic stability of the corn silage. Addition of the buffered propionic acid additive moderately reduced the production of acids during fermentation and resulted in a small reduction in the numbers of yeasts after ensiling, but did not affect aerobic stability. In a second experiment, 30 Holstein cows (4 primiparous and 26 multiparous) averaging 118 +/- 70 d in milk and producing 38 +/- 16 kg of milk/d were fed a total mixed ration, once daily, that consisted of (on a DM basis) 25% corn silage, 15% alfalfa silage, 10% alfalfa hay, and 50% concentrate. One-half of the cows were fed a blend of essential oils that was mixed directly into their total mixed ration to provide 1.2 g/cow per d for 9 wk. Cows fed the essential oils ate 1.9 kg more dry matter/d and produced 2.7 kg more 3.5% fat-corrected milk/d than did cows fed the control diet. The percentages of milk fat and protein, the somatic cell count numbers, and the concentrations of milk urea nitrogen were unaffected by treatment. Feed efficiency, change in body weight, and change in body condition scoring were also similar between treatments. After 12 h of incubation, the addition of a moderate dose and a high dose of essential oils to in vitro ruminal fermentations had no effect on the concentration of total VFA compared with the control treatment. However, they decreased the molar proportions of acetic, butyric, and valeric acids and increased the proportion of propionic acid. The blend of essential oils evaluated in this study altered in vitro ruminal fermentation and improved animal performance when fed directly to cows, but it did not affect the fermentation or aerobic stability of corn silage.

Biosynthesis of plant-derived flavor compounds

Plants have the capacity to synthesize, accumulate and emit volatiles that may act as aroma and flavor molecules due to interactions with human receptors. These low-molecular-weight substances derived from the fatty acid, amino acid and carbohydrate pools constitute a heterogenous group of molecules with saturated and unsaturated, straight-chain, branched-chain and cyclic structures bearing various functional groups (e.g. alcohols, aldehydes, ketones, esters and ethers) and also nitrogen and sulfur. They are commercially important for the food, pharmaceutical, agricultural and chemical industries as flavorants, drugs, pesticides and industrial feedstocks. Due to the low abundance of the volatiles in their plant sources, many of the natural products had been replaced by their synthetic analogues by the end of the last century. However, the foreseeable shortage of the crude oil that is the source for many of the artificial flavors and fragrances has prompted recent interest in understanding the formation of these compounds and engineering their biosynthesis. Although many of the volatile constituents of flavors and aromas have been identified, many of the enzymes and genes involved in their biosynthesis are still not known. However, modification of flavor by genetic engineering is dependent on the knowledge and availability of genes that encode enzymes of key reactions that influence or divert the biosynthetic pathways of plant-derived volatiles. Major progress has resulted from the use of molecular and biochemical techniques, and a large number of genes encoding enzymes of volatile biosynthesis have recently been reported.

Redirecting rumen fermentation to reduce methanogenesis

Methane production in ruminants has received global attention in relation to its contribution to the greenhouse gas effect and global warming. In the last two decades, research programs in Europe, Oceania and North America have explored a variety of approaches to redirecting reducing equivalents towards other reductive substrates as a means of decreasing methane production in ruminants. Some approaches such as vaccination, biocontrols (bacteriophage, bacteriocins) and chemical inhibitors directly target methanogens. Other approaches, such as defaunation, diet manipulations including various plant extracts or organic acids, and promotion of acetogenic populations, seek to lower the supply of metabolic hydrogen to methanogens. The microbial ecology of the rumen ecosystem is exceedingly complex and the ability of this system to efficiently convert complex carbohydrates to fermentable sugars is in part due to the effective disposal of H2 through reduction of CO2 to methane by methanogens. Although methane production can be inhibited for short periods, the ecology of the system is such that it frequently reverts back to initial levels of methane production though a variety of adaptive mechanisms. Hydrogen flow in the rumen can be modelled stoichiometrically, but accounting for H2 by direct measurement of reduced substrates often does not concur with the predictions of stoichiometric models. Clearly, substantial gaps remain in our knowledge of the intricacies of hydrogen flow within the ruminal ecosystem. Further characterisation of the fundamental microbial biochemistry of hydrogen generation and methane production in the rumen may provide insight for development of effective strategies for reducing methane emissions from ruminants.

Effect of plant extracts on methanogenesis and microbial profile of the rumen of buffalo: a brief overview

Plants rich in secondary metabolites (saponins, tannins, essential oils, etc.) have antimicrobial activity which can be exploited for selective inhibition of a particular group of microbes in the rumen. We have screened a large number of plant extracts for their potential to inhibit methanogenesis and ciliate protozoa in an in vitro gas production test using buffalo rumen liquor as the inoculum. Out of 93 plant extracts tested, 11 inhibited in vitro methanogenesis to the extent of 25–50% and nine plant extracts inhibited methanogenesis more than 50%. Among 20 extracts exhibiting antimethanogenic activity, nine were ethanol extracts, 10 were methanol extracts and only one was a water extract. Some of these plant extracts inhibited ciliate protozoa as tested by microscopic examination and 14C-labelled radioisotopic technique, but the protozoa inhibition was not correlated with methane inhibition, indicating that the methanogens sensitive to plant secondary metabolites may or may not be having any symbiotic relationship with ciliate protozoa. Methane inhibition was accompanied by a drastic fall in the number of methanogens as determined by real time PCR. Plants that appeared to have some potential as feed additives to control methanogenesis by the ruminants are: (i) seed pulp of Sapindus mukorossi (rich in saponins) and Terminalia chebula (rich in tannins); (ii) leaves of Populus deltoides, Mangifera indica and Psidium guajava (rich in tannins and essential oils); and (iii) flower buds of Syzygium aromaticum and bulb of Allium sativum (rich in essential oils). Some of the plants reported in literature exhibiting antimethanogenic activity include Equisetum arvense, Lotus corniculatus, Rheum palmatum, Salvia officinalis, Sapindus saponaria, Uncaria gambir and Yucca schidigera.

Linking rumen function to animal response by application of metagenomics techniques

Metagenomics techniques applied to the rumen microbiota have demonstrated tremendous diversity originally among populations of bacteria and, more recently, among the methanogenic archaea, including those associated with protozoa. Although with some potential limitations, cluster analyses of sequences recovered from clone libraries have revealed differences in populations among animals fed forage v. grain, including amylolytic ruminococci and novel groups of clostridia adhering to the rumen particulates. Rapid profiling procedures, such as denaturing gradient gel electrophoresis (DGGE), can be used to infer likely differences in community structure of bacteria and archaea among numerous replicates of animals and times after feeding diets that are more representative of intense ruminant animal production. Metagenomics procedures also are being applied to issues related to ruminal output of fatty acid isomers influencing milk fat composition and consumer acceptance, the environmental impact of nitrogen in animal waste and methane emissions, and future potential approaches to improve ruminal fibre digestibility. If varying concentrations of ruminal metabolites and fluxes quantified from microbial processes can be combined with results from metagenomics applied to rumen microbiota, then we should reduce the unexplained variability in models in which the prediction of nutrient supply to the intestine is synchronised with nutritional guidelines for more efficient feed conversion by ruminants.