Media outlets have recently reported that a new dietary additive for livestock could significantly reduce greenhouse gas emissions from beef and dairy production. [1] The reports were based on a study published in the Proceedings of the National Academy of Sciences. [2]

The chemical methane inhibitor, known as 3-nitrooxypropanol (3NOP), has been found to reduce methane emissions from the process of enteric fermentation within a cow’s digestive system by up to 30 percent.

Despite the beneficial finding, the potential reduction still leaves overall emissions from beef production on a different paradigm to those of alternative products.

There are two key reasons.

  • Firstly, methane emissions from enteric fermentation only represent a portion of the emissions from beef production, leaving many other sources that are unaffected by the change.
  • Secondly, apart from dairy cows, it may generally only be possible to apply the additive during a relatively short portion of many cows’ lives, and possibly not at all for those raised entirely on grass. For example, in Australia, the authors of a recent peer-reviewed paper wrote that “feed manipulation mitigation has low potential, because beef feedlots produce just 3.5% of enteric fermentation emissions”. [3]

The findings are only materially relevant to ruminant animals, and would appear to have little or no impact on emissions from products such as chicken or pig meat. (The Food and Agriculture Organization of the United Nations (FAO) has reported zero enteric fermentation emissions from chickens, and 3.1% from pigs). [4]

Figure 1 shows the estimated impact of the new additive on beef’s emissions intensity, assuming it were to become readily available with similar results to those found in the research study. (Emissions intensity represents the kilograms of carbon dioxide-equivalent, or CO2-e, greenhouse gases per kilogram of product.) The findings indicate that the 30 percent reduction in methane emissions achieved while consuming the inhibitor equates to a reduction of around 8.8 percent in overall emissions intensity for beef (94 kg compared to 83 kg).

Figure 1: Emissions intensity with and without 3NOP enteric methane inhibitor with GWP20 (kg CO2-e/kg product)


The results in Figure 1 are based on global average figures for:

  • the specialised beef herd;
  • the dairy herd; and
  • combined dairy and specialised beef

The figures vary by region, and are influenced by factors such as feed digestibility, livestock management practices, reproduction performance and land use.

The emissions intensity of beef from the dairy herd is lower than that of specialised beef. The main reason is that a large portion of the dairy herd’s emissions are attributed to dairy products, such as milk and cheese. The emissions from a dairy cow may be similar to those from a cow raised solely for beef, but the emissions per kilogram of product from a dairy cow are spread across a broader range of products than those from a cow in the specialised beef herd.

The emissions intensity of cow’s milk would reduce 18.5 percent, from 5.7 kilograms to 4.7 kilograms CO2-e per kilogram of product.

The figures are based on a twenty-year time horizon for determining the “global warming potential” (GWP) of the various greenhouse gases. Such a time frame, which more accurately reflects the shorter-term impacts of methane emissions, is critical when considering climate change tipping points, with potentially catastrophic and irreversible impacts.

For the purpose of the calculations, it is assumed it would be possible, using the 3NOP inhibitor, to influence the following percentages of the enteric fermentation emissions that would otherwise have applied:

  • Specialised beef (mixed feeding systems): 50 percent
  • Specialised beef (grazing systems): Nil
  • Dairy beef (mixed feeding systems): 100 percent
  • Dairy beef (grazing systems): Nil

The extent of the inhibitor’s influence was determined to be the product of the 30 percent figure reported by the researchers, and the relevant percentages shown above, weighted by production levels.

Although cows in mixed feeding systems within the specialised beef herd generally only spend the final 10 to 25 percent of their lives in feedlots, they reach their maximum size (and greenhouse gas-emitting capacity) during that period.

The figure of 50 percent has been arrived at after considering typical weights and feeding periods from North American production systems, where the use of feedlots is more prominent than in a country such as Australia. [5] [6] Even then, the figure of 50 percent is at the high end of the likely range, thereby potentially overstating the benefit of the inhibitor. That is a conservative approach in the context of this article’s message, which is that the inhibitor’s benefits are not as significant as may have been assumed from initial media reports. On the other hand, the inhibitor was found to increase body weight gain, which would contribute to a reduction in emissions intensity.

As indicated, a figure of 100 percent has been assumed for cows in mixed feeding systems within the dairy herd, where production infrastructure may provide greater opportunities than in the specialised beef herd to apply the inhibitor. That assumes that the animals can receive mainly non-grain feed such as hay and alfalfa for extended periods, as they have not evolved to eat grains, and would only survive on them for a limited time. The researchers have reported that the inhibitor needs to be delivered continuously into the cow’s rumen in order to be effective, meaning it would need to be mixed with the daily allotment of feed. The researchers stated: “If delivered as a pulse-dose, the inhibitory effect will likely be transient.”

The figures have been adapted from emissions intensity and production figures published by the FAO in 2013. [7] The emissions intensity figures are based on the global average percentage apportionment of the various contributing factors, and are intended to be approximations only.

Figure 2 indicates how different types of beef, with the benefit of the 3NOP inhibitor, compare to some plant-based alternatives. The emissions intensity figures for the latter are from a 2014 Oxford University study. [8] Of note is the fact that soy beans contain nearly 50 percent more protein than beef per kilogram. [9]

Figure 2: Emissions intensity of beef with 3NOP enteric methane inhibitor relative to plant-based options with GWP20 (kg CO2-e/kg product)


Figures 3 and 4 show the kilograms of carbon dioxide-equivalent greenhouse gas emissions from 1 kilogram of beef, with and without the 3NOP enteric methane inhibitor. Firstly, without the inhibitor:

Figure 3: kg of CO2-e emissions per kg of beef without 3NOP enteric methane inhibitor (global ave. incl. dairy herd beef based on 20-year GWP)


Secondly, with the inhibitor:

Figure 4: kg of CO2-e emissions per kg of beef with 3NOP enteric methane inhibitor (global ave. incl. dairy herd beef based on 20-year GWP)



Attempts at reducing methane emissions from livestock receive significant attention, but little is said by mainstream media or environmental groups about the far more effective option of reducing meat consumption. If we are serious about addressing climate change, then that is an essential measure.


Paul Mahony (also on Twitter, Scribd, Slideshare and Viva la Vegan)


[1] Gray, D., “Diet change cuts methane emissions in cow burps”, The Age, 4th August, 2015, http://www.theage.com.au/victoria/diet-change-cuts-methane-emissions-in-cow-burps-20150804-girf6l.html

[2] Hristov, A.N., Oh, J., Giallongo, F., Frederick, T.W., Harper, M.T., Weeks, H.L., Branco, A.F., Moate, P.J., Deighton, M.H., Williams, S.R.O., Kindermann, M., Duval, S., An inhibitor persistently decreased enteric methane emission from dairy cows with no negative effect on milk production“, Proceedings of the National Academy of Sciences, PNAS 2015 ; published ahead of print July 30, 2015, doi:10.1073/pnas.1504124112, http://www.pnas.org/content/early/2015/07/29/1504124112.full.pdf

[3] Wedderburn-Bisshop, G., Longmire, A., Rickards, L., “Neglected Transformational Responses: Implications of Excluding Short Lived Emissions and Near Term Projections in Greenhouse Gas Accounting”, International Journal of Climate Change: Impacts and Responses, Volume 7, Issue 3, September 2015, pp.11-27. Article: Print (Spiral Bound). Published Online: August 17, 2015, http://ijc.cgpublisher.com/product/pub.185/prod.269

[4] Food and Agriculture Organization of the United Nations, “Tackling climate change through livestock: A global assessment of  emissions and mitigation opportunities”, Nov 2013, Figure 18, p. 35 and Figure 20, p. 37, http://www.fao.org/ag/againfo/resources/en/publications/tackling_climate_change/index.htm; http://www.fao.org/docrep/018/i3437e/i3437e.pdf

[5] Ontario Ministry of Agriculture, Food and Rural Affairs, “Typical Beef Feedlot and Background Diets – Factsheet”, March, 2006, http://www.omafra.gov.on.ca/english/livestock/beef/facts/06-017.htm

[6] Goodman, R., Agriculture Proud, “Ask A Farmer: What do feedlot cattle eat?”, 9th October, 2012, http://agricultureproud.com/2012/10/09/ask-a-farmer-what-do-feedlot-cattle-eat/

[7] Food and Agriculture Organization of the United Nations, op cit., Figure 7 and Table 5, p. 24

[8] Scarborough, P., Appleby, P.N., Mizdrak, A., Briggs, A.D.M., Travis, R.C., Bradbury, K.E., & Key, T.J., “Dietary greenhouse gas emissions of meat-eaters, fish-eaters, vegetarians and vegans in the UK”, Climatic Change, DOI 10.1007/s10584-014-1169-1, http://link.springer.com/article/10.1007%2Fs10584-014-1169-1

[9] USDA National Nutrient Database for Standard Reference at http://ndb.nal.usda.gov/ via Nutrition Data at http://www.nutritiondata.com


Dairy Cows Photo © Nengloveyou | Dreamstime.com