August 1, 2024
In 2022, I gave a presentation about climate change solutions to the Canadian Parliament. During that meeting, I had the opportunity to hear a presentation from a beef producers group about how they intended to rely on a new synthetic methane inhibitor (not approved in Canada at the time) as the heart of efforts to curb their greenhouse gas emissions.
I was aware that some compounds might be able to reduce methane from ruminant livestock, but not that any of the options had stepped so far into the limelight. As I listened to the presentation, I began to wonder: could such interventions be the key to truly climate-friendly meat? Or would they become yet another tool in the arsenal of agricultural greenwashing? How much potential do feed additives actually have, and how ready are they?
Ruminants are a class of livestock that includes cattle, goats, sheep, and more. Their remarkable digestive system contains multiple fermentation chambers that allow them to live on grass and leaves alone – a feat that other animals like pigs, poultry, and humans cannot do. This “enteric” fermentation is, unfortunately, a major global source of methane – a very potent greenhouse gas that is many times more warming in the near term than carbon dioxide.
These emissions, produced by certain microbes and belched by the ruminants during digestion, actually indicate wasted food, an inefficiency that could have otherwise contributed to producing more meat or milk. Methane is made of carbon and hydrogen and is released from the rumen. Those same carbon and hydrogen atoms could instead be combined into digestible compounds, contributing to meat or milk production. In effect, methane emissions represent food eaten by “freeloading” microbes that live in the rumen and hijack their host’s food for themselves.
Roughly 21% of humanity’s methane emissions are from enteric fermentation.
Lately, there has been a lot of buzz about adding seaweeds and other ingredients to livestock feed to reduce methane emissions from ruminant animals. (Note this is different than improving cattle feed by switching to high-quality forage such as legumes.) This is understandable. These methane emissions are a big problem; they total 2.1 gigatons of carbon dioxide equivalents per year (Gt CO2-eq/yr), projected to rise to 3.4 gigatons by 2050. Roughly 21% of humanity’s methane emissions are from enteric fermentation. By comparison, all of the world’s flights in 2022 released 0.8 gigatons of carbon dioxide.
Additives make up only about 1% of the feed consumed in a day, but they suppress the action of the group of microbes that produce methane. While much of the discussion in the press has focused on Asparagopsis seaweed, it is only one of hundreds of options within a cluster of several broad classes. (One recent meta-analysis investigated 170 types of methane-reducing feed additives.)
However, of those many additives, just a few have been studied well enough to have predictable outcomes and proper doses, and even fewer are actually in use by farmers, ranchers, or pastoralists.
These categories include plant-based oils, seaweeds, alternative electron acceptors, ionophores, methane inhibitors, phytochemicals, and essential oils. Most of these categories feature many options, though most still need to be thoroughly tested, and few are in wide use yet.
Across these additives, the resulting methane reductions tend to be around 10-30%, a helpful contribution but far from enough to stave off the planet-warming effects of enteric fermentation. In a promising development, initial studies have shown that some different additives can be used together for greater effect. For example, combining 3-NOP with plant-based oils provides a more significant impact than either one alone.
The IPCC reports that the theoretical maximum potential for reducing enteric methane emissions is 0.8 Gt CO2-eq per year, out of the 2.1 Gt total enteric methane emissions, a maximum reduction of 38%. However, of this technical potential, only 0.2 Gt is economically achievable. What’s more, that total includes feed additives and other strategies like breeding for lower emissions and feeding concentrates. So, only about 10% of enteric methane can be reduced, and feed additives are only a subset of that.
Let’s examine two of the most publicized options: Asparagopsis seaweed and 3-NOP.
Two species of Asparagopsis seaweed have been identified with potential as methane inhibitors. There are not yet enough data to be decisive, but reductions range widely. In some cases, livestock show lower milk production and reduced appetite. Bill Gates and others have invested millions of dollars in a startup that is looking to synthesize the key ingredients in Asparagopsis for broad commercialization.
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Asparagopsis seaweed in its natural environment. Credit: Jean-Pascal Quod / Wikimedia Commons
3-NOP (marketed as Bovaer) is a synthetic methane reducer that looks like the first out of the gate for broad adoption. It has been approved for use in 55 countries since 2021, but data about how much it is in use are not yet available. The IPCC rates chemical inhibitors like 3-NOP as a promising and emerging strategy for the near term, and studies show it reduces methane emissions by an average of 32.5%. That’s enough to be important, but far from solving the problem of ruminant methane.
Why such a low potential impact?
