PREDICCIÓN Y MITIGACIÓN DE LAS EMISIONES DE METANO DE LOS RUMIANTES

Livestock production systems emit enteric methane originated in rumen fermentation. There is growing interest in controlling methane production in the rumen because of its effects on climate change and the energy utilization inefficiency implied by methane losses to the atmosphere. There are currently several strategies of enteric methane abatement being investigated: nutrition, selection of low emitting animals, intensification of production, plant secondary compounds, chemical inhibitors, nitrate, immunization, defaunation, reductive acetogenesis, and bacteriophages. Research is also performed in developing predictive models of methane emissions based on animal production or diet composition, which can be used to build inventories of greenhouse gases emissions by country, region or sector.Los sistemas ganaderos son altos emisores de metano entérico proveniente de la fermentación en el rumen. Existe interés creciente en controlar la producción de metano en el rumen debido a sus efectos ambientales y la pérdida de energía que supone. Varias estrategias de mitigación de la producción de metano por los rumiantes están siendo investigadas, como alimentación, selección de animales de baja emisión, intensificación de la producción animal, compuestos secundarios de plantas, inhibidores químicos, nitrato, inmunización, defaunación, acetogenesis reductiva, y bacteriófagos. Adicionalmente, se investiga en el desarrollo de modelos predictivos de la producción de metano entérica en función de la producción de leche o la composición de la dieta para construir inventarios de emisiones de gases de efecto invernadero por países, regiones o sectores

Evaluating the effect of phenolic compounds as hydrogen acceptors when ruminal methanogenesis is inhibited in vitro – Part 1. Dairy cows

Some antimethanogenic feed additives for ruminants promote rumen dihydrogen (H) accumulation potentially affecting the optimal fermentation of diets. We hypothesised that combining an H acceptor with a methanogenesis inhibitor can decrease rumen H build-up and improve the production of metabolites that can be useful for the host ruminant. We performed three in vitro incubation experiments using rumen fluid from lactating Holstein cows: Experiment 1 examined the effect of phenolic compounds (phenol, catechol, resorcinol, hydroquinone, pyrogallol, phloroglucinol, and gallic acid) at 0, 2, 4, and 6 mM on ruminal fermentation for 24 h; Experiment 2 examined the combined effect of each phenolic compound from Experiment 1 at 6 mM with two different methanogenesis inhibitors (Asparagopsis taxiformis or 2-bromoethanesulfonate (BES)) for 24 h incubation; Experiment 3 examined the effect of a selected phenolic compound, phloroglucinol, with or without BES over a longer term using sequential incubations for seven days. Results from Experiment 1 showed that phenolic compounds, independently of the dose, did not negatively affect rumen fermentation, whereas results from Experiment 2 showed that phenolic compounds did not decrease H accumulation or modify CH production when methanogenesis was decreased by up to 75% by inhibitors. In Experiment 3, after three sequential incubations, phloroglucinol combined with BES decreased H accumulation by 72% and further inhibited CH production, compared to BES alone. Interestingly, supplementation with phloroglucinol (alone or in combination with the CH inhibitor) decreased CH production by 99% and the abundance of methanogenic archaea, with just a nominal increase in H accumulation. Supplementation of phloroglucinol also increased total volatile fatty acid (VFA), acetate, butyrate, and total gas production, and decreased ammonia concentration. This study indicates that some phenolic compounds, particularly phloroglucinol, which are naturally found in plants, could improve VFA production, decrease H accumulation and synergistically decrease CH production in the presence of antimethanogenic compounds.This work was supported by the EU Horizon 2020 research and innovation program under grant agreement No 818368 (MASTER). RH was supported by the China Scholarship Council. AB has a Ramón y Cajal Research Contract (RYC 2019-027764-I) funded by the Spanish Research Agency (AEI: 10.13039/501100011033)

Review: Reducing enteric methane emissions improves energy metabolism in livestock: is the tenet right?

The production of enteric methane in the gastrointestinal tract of livestock is considered as an energy loss in the equations for estimating energy metabolism in feeding systems. Therefore, the spared energy resulting from specific inhibition of methane emissions should be re-equilibrated with other factors of the equation. And, it is commonly assumed that net energy from feeds increases, thus benefitting production functions, particularly in ruminants due to the important production of methane in the rumen. Notwithstanding, we confirm in this work that inhibition of emissions in ruminants does not transpose into consistent improvements in production. Theoretical calculations of energy flows using experimental data show that the expected improvement in net energy for production is small and difficult to detect under the prevailing, moderate inhibition of methane production (≈25%) obtained using feed additives inhibiting methanogenesis. Importantly, the calculation of energy partitioning using canonical models might not be adequate when methanogenesis is inhibited. There is a lack of information on various parameters that play a role in energy partitioning and that may be affected under provoked abatement of methane. The formula used to calculate heat production based on respiratory exchanges should be validated when methanogenesis is inhibited. Also, a better understanding is needed of the effects of inhibition on fermentation products, fermentation heat, and microbial biomass. Inhibition induces the accumulation of H2, the main substrate used to produce methane, that has no energetic value for the host, and it is not extensively used by the majority of rumen microbes. Currently, the fate of this excess of H2 and its consequences on the microbiota and the host are not well known. All this additional information will provide a better account of energy transactions in ruminants when enteric methanogenesis is inhibited. Based on the available information, it is concluded that the claim that enteric methane inhibition will translate into more feed-efficient animals is not warranted

Invited review: Current enteric methane mitigation options

peer-reviewedRuminant livestock are an important source of anthropogenic methane (CH4). Decreasing the emissions of enteric CH4 from ruminant production is strategic to limit the global temperature increase to 1.5°C by 2050. Research in the area of enteric CH4 mitigation has grown exponentially in the last 2 decades, with various strategies for enteric CH4 abatement being investigated: production intensification, dietary manipulation (including supplementation and processing of concentrates and lipids, and management of forage and pastures), rumen manipulation (supplementation of ionophores, 3-nitrooxypropanol, macroalgae, alternative electron acceptors, and phytochemicals), and selection of low-CH4-producing animals. Other enteric CH4 mitigation strategies are at earlier stages of research but rapidly developing. Herein, we discuss and analyze the current status of available enteric CH4 mitigation strategies with an emphasis on opportunities and barriers to their implementation in confined and partial grazing production systems, and in extensive and fully grazing production systems. For each enteric CH4 mitigation strategy, we discuss its effectiveness to decrease total CH4 emissions and emissions on a per animal product basis, safety issues, impacts on the emissions of other greenhouse gases, as well as other economic, regulatory, and societal aspects that are key to implementation. Most research has been conducted with confined animals, and considerably more research is needed to develop, adapt, and evaluate antimethanogenic strategies for grazing systems. In general, few options are currently available for extensive production systems without feed supplementation. Continuous research and development are needed to develop enteric CH4 mitigation strategies that are locally applicable. Information is needed to calculate carbon footprints of interventions on a regional basis to evaluate the impact of mitigation strategies on net greenhouse gas emissions. Economically affordable enteric CH4 mitigation solutions are urgently needed. Successful implementation of safe and effective antimethanogenic strategies will also require delivery mechanisms and adequate technical support for producers, as well as consumer involvement and acceptance. The most appropriate metrics should be used in quantifying the overall climate outcomes associated with mitigation of enteric CH4 emissions. A holistic approach is required, and buy-in is needed at all levels of the supply chain