Dairy Sustainability Part 2: Methane Mitigating Feed Additives

Dr. Kirby Krogstad, Assistant Professor, Department of Animal Sciences, The Ohio State University and Dr. Joanne Knapp, Fox Hollow Consulting, LLC

As we discussed in the first article of our series, enteric methane, produced in the digestive tract of dairy cows, is one of the largest greenhouse gas emission sources on a dairy farm. Fortunately, there are a tremendous number of interventions being investigated for their potential to reduce enteric methane emissions. These include compounds like 3-nitrooxypropanol (3-NOP; Bovaer), monensin (Rumensin), essential oils (Agolin, Mootral), seaweed (Asparagopsis species), nitrate, saponins, tannins, and direct fed microbials. In this brief article, we’re going to focus on the two most potent methane mitigators (3-NOP and Asparagopsis) and two commercially available products (monensin and essential oils) which have associated carbon credits. At this time, 3-NOP and Asparagopsis are not approved for livestock feed in the United States.

What is the Story on Each Additive?

For an in-depth discussion and description of the potential methane mitigating feed additives, I’d refer you to an excellent and thorough review by Hegarty et al. (2021; Table 1).  They discuss not only the methane mitigation potential but also bottlenecks, limitations, and future challenges to their use.

The two most potent enteric methane mitigating feed additives are 3-NOP and Asparagopsis. Both act as methane inhibitors, which means they interfere with the process that microbes use to synthesize methane in the rumen. They are currently under development and are not commercially available in the United States as of this writing.

With over 30 feeding studies, 3-NOP has a rigorous and highly consistent body of evidence that demonstrates it reduces enteric methane emissions on average by 20 to 40% without affecting feed intake or milk yield (Kebreab et al., 2023). It does slightly increase milk fat – a 0.19 unit increase in milk fat percentage which translates to an increase of 0.2 lb/day of milk fat (Hristov et al., 2022).

Asparagopsis, a genus of seaweed, has reduced methane from dairy cattle by up to 67% (Roque et al., 2019). Unfortunately, as inclusion rates increased, it also reduces feed intake, so determining the optimal feeding dose will be critical. Generally, as Asparagopsis inclusion increased, it also reduced milk, milk fat, and milk protein yields. Another challenge for using Asparagopsis is that it reduces methane because it contains bromoform compounds which are carcinogens that can be transferred to milk (Stefenoni et al., 2021) and meat and may also contribute to ozone depletion. While Asparagopsis is a potent methane mitigant, it has many challenges to overcome before it can be widely used.

Monensin and essential oils, both of which are commercially available for cattle now and have associated carbon credits being marketed with them, are rumen modulators. They do not directly inhibit methane but alter rumen fermentation or the rumen microbiota in such a way that they reduce methane produced during fermentation. Monensin has been exhaustively investigated in cattle over the past 40 years. A recent meta-analysis with 18 experiments observed that methane was reduced by 5% when monensin was fed (Marumo et al., 2023). Whether the reduction in enteric methane is sustained over time with feeding monensin is unknown (Knapp et al., 2014; Marumo et al., 2023). The upside for monensin is that it reduces feed intake and increases milk yield, thus increasing feed efficiency (Duffield et al., 2008). 

Essential oils have also shown promise but are complicated. Essential oils are metabolites isolated from plants, and there are literally thousands of these compounds which exist. The compounds have been isolated from things like garlic, thyme, and cinnamon (Beauchemin et al., 2020). Some of these compounds have reduced methane production in vitro, but when fed to a cow, the data are less consistent. Some essential oil blends have shown promise when fed to dairy cattle. A meta-analysis from Belanche et al. (2020) suggested that an essential oil blend reduced methane production by 8.8%, increased milk yield by 4%, and increased feed efficiency by 4%. Unfortunately, much of the data in the analysis were unpublished field reports so conclusions should be drawn carefully. Hegarty et al. (2021) specifically noted that additional properly designed research is necessary to increase confidence in the efficacy of essential oils to reduce methane production in cattle. Nonetheless, there are programs paying dairy farmers for the potential carbon mitigation from essential oils (e.g., Agolin and Mootral).

Does Mitigating Methane Pay?

This is the $1 million question – so to speak. Currently, the carbon credits accumulated from mitigating methane through feed additives is valued at approximately $30/ton CO2e (carbon dioxide equivalents). With that in mind, does it pay to feed monensin or essential oils to reduce the enteric methane that cows produce?

For this exercise, we assumed that we had a 1,000 milking cows. We assumed that both supplements cost $0.055 animal/day to feed, which means it costs $20,075 to supplement 1,000 milking cows for 365 days. The current protocol for monensin assumes a methane reduction of 5%, while the protocol for a commercial essential oil blend is approximately 8.8% which equates to approximately 20 and 35 g of methane mitigated per cow per day, respectively.  At a carbon price of $30/ton of CO2e, feeding monensin to 1,000 cows for 1 year would generate in $6,745 in revenue, while feeding essential oils would generate $11,871 (Figure 1). The methane mitigation alone does not cover the cost of supplementation but that is without factoring in performance benefits which may occur. Currently, the methane mitigation payments may act as a subsidy to feed these additives, thereby increasing the return on investment when the performance benefits are factored in. For your own investigations – please use our Dairy C Calculator.

Who are buying and selling these carbon credits? How is the market working? What should be expected in the future? We’ll dive into some of that in the final article of our dairy sustainability series.

Table 1. Summary of methane reduction potential and level of confidence in various feed additives.1


Methane Reduction Potential

Confidence in Efficacy2




Essential oils




Very High



Very High


1Data from Hegarty et al. (2021)
2Confidence in efficacy rated on a 1 to 5 scale, with 1 corresponding to low agreement and limited evidence and 5 corresponding to high   agreement and robust evidence.

 Figure 1. Potential methane mitigation payments from feeding monensin or essential oils depending on the price of carbon credits ($/ton CO2e). The horizontal black line is total cost of feeding the supplements (breakeven point).


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Belanche, A., C. J. Newbold, D. P. Morgavi, A. Bach, B. Zweifel, and D. R. Yáñez-Ruiz. 2020. A meta-analysis describing the effects of the essential oils blend Agolin Ruminant on performance, rumen fermentation and methane emissions in dairy cows. Animals (Basel) 10(4). 10.3390/ani10040620

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