Anti-Methane Livestock Vaccines Are Nascent
Impact: 4-5% Global Warming Potential (GWP) Technology Maturity: Lab
Following up my ClimateTech Market Map, this is the second note of a series on specific climate technologies, with a deeper dive into their technical maturity and their potential to reduce global warming. (My last note covered the de-carbonization of nitrogen fertilizer.)
Livestock digestion and livestock manure are major sources of anthropogenic methane emissions, representing ~ 4-5% of global warming potential (GWP) (1). Of these, digestive sources (enteric methane) contributes 90% of that GWP and two-thirds of that 90% is from beef and dairy cattle. Technologies that can reduce or eliminate enteric methane emissions from cattle therefore have the potential to make a large contribution to getting to net zero. However, technical solutions for reducing enteric emissions are currently underwhelming and investment in the area dramatically lags other essential categories such as solar photo-voltaic or battery technologies.
The Enteric Methane Production Process
Livestock enteric methane is produced as a side effect when microbes convert food in the rumen (the first of a cow's four digestive compartments) - into volatile fatty acids that the cow can later absorb. Populations of archaea, representing about 5% of the total microbiome by weight, are responsible for methane emissions. These archaea take the plentiful waste hydrogen emitted by other rumen microbes during their own digestive processes and combine it with carbon dioxide to produce methane. (There are also other less important methanogenic pathways.)
Quite apart from emissions, methane production constitutes a substantial diversion of food energy that would otherwise be used by the animal for milk production or growth: anywhere from 2-12% of total food intake. Diverting this energy back to products that cattle can absorb could also improve livestock productivity as a side-effect.
On first look, therefore, from an energy perspective archaea behave like parasites. However, the benefit of methane production to the animal is that it removes the hydrogen waste emitted by other microbiome bacteria, which could otherwise accumulate and acidify the rumen. Acidification can cause acidosis which can lead in turn to liver abscesses, lameness, lack of appetite and problems with milk production and quality (2). So in fact, the animal/methanogen relationship is not parasitic, but one of mutual benefit: the archaea get to feed on hydrogen and the cow gets its rumen pH maintained at a healthy level.
Given the important role of methane as a hydrogen sink, it would seem impossible to inhibit its production and still maintain animal health. But fortunately, this is not true. Other rumen microbes can also eliminate hydrogen without producing methane. Instead of producing methane, they incorporate hydrogen into substances such as propionate and succinate that can be absorbed by the cow.
The task for any inhibition technology is therefore is to selectively inhibit the methanogenic microbes while protecting the alternative hydrogen scavengers: all without de-stabilizing the complex (and largely under-characterized) relationships among the other microbiome species of bacteria, fungi and protozoa.
Approaches to Reduce Enteric Methane
Broadly speaking there are three approaches to reducing enteric methane emissions: feed manipulation & supplementation, vaccination, and air filtration. Of the three approaches, vaccination promises to have the widest applicability. An effective vaccine would work easily for both pastured and housed cattle and would likely be highly cost-effective enabling global use.
The goal of a successful vaccine is to stimulate the immune system to secrete anti-bodies into saliva that are then carried intact into the rumen. Once in the rumen, the anti-bodies have to remain intact long enough to bind preferentially to methanogenic archaea and disrupt their functioning. The anti-bodies have to be produced in saliva because the rumen does not secrete any substances directly because the rumen is essentially a large leather bag.
Vaccine Progress
The most recent systematic review of enteric methane vaccine research is by Baca-Gonzalez et al. (2020). Their paper found just seven published studies that measured methane emissions after vaccination either in vitro or in vivo. In vitro treatments which used cultured rumen fluid or an artificial rumen, were largely effective at significant methane reduction. However, only a single treatment from a single study showed significant methane emissions reduction in a live animal (a sheep). All other treatments in live animals showed no response: demonstrating a significant translation gap between lab and field.
In general, antibody response was transient with highly variable latency from application to peak concentration, requiring frequent boosters. However, the researchers also observe that methodologies varied greatly between experiments making cross comparison difficult.
Vaccine Startups
Research on anti-methane vaccines is primarily supported by non-commercial sources. The Pastoral Greenhouse Gas Research Consortium is funding research in New Zealand. A collaboration between the Royal Veterinary College and the Pirbright Institute in the UK is being supported by the Bezos Earth Fund.
Arkea Bio is a New Zealand startup that has raised $26.5M to develop a working vaccine and is in its early developmental stages.
Conclusions
Vaccination strategies for abating enteric methane emissions are essentially at the starting line and the funding devoted to this approach seems low compared to the scale of the research required to adequately characterize methanogens and the rumen microbiome. Many, many challenges need to be solved to translate promising in vitro results to live animals, and then those approaches need to be tested in a wide range of cattle and conditions to reflect the diversity of genetics and forage sources in the field.
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The Climate Change Impacts Series
References
(1) EPA, 2013. "Global Mitigation of Non-CO2 Greenhouse Gases: 2010-2030." EPA, Washington D.C. Available online at: https://www.epa.gov/sites/default/files/2016-06/documents/mac_report_2013.pdf
Baca-González, V., Asensio-Calavia, P., González-Acosta, S., Pérez de la Lastra, J.M. and Morales de la Nuez, A., 2020. Are vaccines the solution for methane emissions from ruminants? A systematic review. Vaccines, 8(3), p.460.
Pitta, D., Indugu, N., Narayan, K. and Hennessy, M., 2022. Symposium review: Understanding the role of the rumen microbiome in enteric methane mitigation and productivity in dairy cows. Journal of Dairy Science, 105(10), pp.8569-8585.
Söllinger et al., 2018. Holistic assessment of rumen microbiome dynamics through quantitative metatranscriptomics reveals multifunctional redundancy during key steps of anaerobic feed degradation. MSystems, 3(4), pp.10-1128.