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| Fig. 1: Global monthly mean CH4 concentration. [4] (Courtesy of NOAA) |
In the tens of thousands of years that humanity has existed in its anatomically modern form, it has transformed the planet more than almost any other organism. Whether by hunting the Pleistocene megafauna into extinction, the development of agriculture, or the industrial revolution, humans have consistently been altering the planet. [1] Today, humans number 7.8 billion, meaning that there are thousands of ways that we are changing our environment. Climate change is one of the greatest threats of our time and there are a number of ways that humans are contributing to it. But one of the greatest contributors is not even humans at all, it is domesticated cattle.
In 2015, there were 1.4 billion cows on planet earth. [2] Every single one of these cows, and all other ruminants, produce methane gas. Cows greatly outnumber all other species of ruminants and emit a disproportionate amount of methane. New and accurate data is difficult to come by, but scientists estimate that each individual cow is capable of emitting between 160 and 400 grams of methane per day, depending on a variety of factors with the cows. [3] Although scientists know that atmospheric levels of methane are on the rise, what is directly attributed to cattle is very hard to measure. It must be noted that cows are not solely responsible for the increases observed in Fig. 1. [4] There are also natural methane sinks which take up methane emitted from all sources, natural and unnatural. This means that all the methane produced by cows and other ruminants does not automatically become part of the atmospheric increase. Domestic cows are also not the largest source of human-produced methane, but they contribute to it nonetheless. Today, studies have shown that domestic ruminants are responsible for 37% of all the methane emissions from human activity. [5] Methane is a greenhouse gas that helps retain heat in the atmosphere, just like carbon dioxide. The levels of methane in the atmosphere may be lower than carbon dioxide, but the issue is that methane is far better at trapping heat. In fact, it is about twenty-five times better at this than carbon dioxide. [6] Cows produce methane through digestion and then emit this gas through belching and flatulence. This process, called methanogenesis, is a byproduct of the microbial fermentation that occurs in the rumen and large intestine of the animals known as ruminants, a group that cows are a part of. [7] The microbes involved in this process are called methanogens. [7] These microbes are active at the tail end of digestion and they produce methane through a chemical process in which they reduce (add electrons) carbon dioxide (CO2) to methane (CH4) using two molecules of diatomic hydrogen (H2). [7]
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| Fig. 2:A molecule of the methane (CH4). (Source: Wikipedia Commons) |
Aside from the sheer number of cows being one of the reasons there is so much methane, the feed that cows are given is also a major factor. Whether cows eat only grass or only grain (corn, soy, barley, etc.), they are still emitting huge amounts of methane. [8] But there are certain foods that can be added to a cows diet in order to mitigate that amount of methane produced. One of these promising additives is linseed, commonly known as flax. The supplementation of plant-based fats into the diets of the cows helps because when cows digest fibrous carbohydrates, whether it be grains or grasses, the methanogens break this down and the end product is methane. [9] By reducing the fibrous carbohydrate portion and increasing the lipid-based portion, less methane is produced by the methanogens because of the ease of digestion. [9] Certain populations of cattle that were tested have methane emissions that were reduced by up to 30%. [10] But linseed is not the only additive that can reduce methane emissions. Green tea extract and oregano are other supplements that are being considered. Green tea contains polyphenols and oregano contains essential oils, both of which have the potential to act as antimicrobials. [11] While both of these additives are newer than the plant-based fats like linseed and are still going through rigorous research, they do hold great promise as well and have been tested for adverse effects on the cows and milk with no results. [11]
One of humanity's most important food sources has become a major obstacle in the fight against climate change, but there is a more reasonable solution than every person on the planet going vegetarian. If humans invest in the research necessary to find out how to best mitigate cattle methane emissions through diet additives and also pressure cattle farms to incorporate them, there is the potential for, hopefully, a drastic reduction. This would leave one less problem for future humans, and the same amount of meat on the table.
© Zack LaGrange. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] S. Vavrus et al., "Glacial Inception in Marine Isotope Stage 19: An Orbital Analog for a Natural Holocene Climate," Sci. Rep. 8, 10213 (2018).
[2] T. Robinson et al., "Mapping the Global Distribution of Livestock," PLOS One 9, e96084 (2014).
[3] J. Broucek, "Production of Methane Emissions from Ruminant Husbandry: A Review, J. Environ. Prot. 5, 51796 (2014).
[4] E. J. Dlugokencky et al., "The Growth Rate and Distribution of Atmospheric Methane," J. Geophys. Res. 99, 17021 (1994).
[5] H. Steinfeld et al., "Livestock's Long Shadow," Food and Agriculture Organization of the United Nations, 2006.
[6] D. Reay, P. Smith, and A. van Amstel, "Methane Sources and Global Methane Budget," in Methane and Climate Change, ed. by D. Reay, P. Smith and A. van Amstel (Routledge, 2010).
[7] D. Boadi et al., "Mitigation Strategies to Reduce Enteric Methane," Can. J. Anim. Sci. 84, 319 (2004).
[8] T. Haspel, "Is Grass-Fed Beef Really Better For You, the Animal and the Planet?" Washington Post, 23 Feb 15.
[9] C. Benchaar et al., "Linseed Oil Supplementation to Dairy Cows Fed Diets Based on Red Clover Silage or Corn Silage: Effects on Methane Production, Rumen Fermentation, Nutrient Digestibility, N Balance, and Milk Production," J. Dairy Sci. 98, 7993 (2015).
[10] S. Marette and G. M Millet, "Economic Benefits From Promoting Linseed in the Diet of Dairy Cows," Food Policy 46, 140 (2014).
[11] G. J. Kolling et al., "Performance and Methane Emissions in Dairy Cows Fed Oregano and Green Tea Extracts as Feed Additives", J. Dairy Sci. 101, 4221 (2018).
