Why & How Do Cows Produce Methane? Let’s Know!
Why do cows produce methane?
Cows produce methane because they are ruminants and so they have millions of methanogens in their rumen that utilize the Carbon dioxide (CO2) and Hydrogen (H2) molecules to make methane (CH3).
These Carbon dioxide (CO2) and Hydrogen (H2) molecules are produced from other millions of anaerobic bacteria that are not methanogens, present in the cows’ rumen during the process of fermentation of the forage (ingested food) in the rumen.
The acting of methanogens is the prominent reason why methane is produced. Methanogens generate ATP energy for themselves by synthesizing methane under strictly anaerobic conditions in the rumen.
The formation of methane in cows is actually a type of hydrogenotrophic methanogenesis because it uses H2 for the reduction of CO2.
The reaction of hydrogenotrophic methanogenesis by the methanogens in the cows’ rumen is mentioned below. Kindly take note of this:
4H2 + CO2 → CH4 + 2H2O
Cows are called ruminants because just like other ruminant animals that include cattle, sheep, goats, buffalo, deer, elk, giraffes, and camels, cows also have a four-chambered stomach which is a part of their big digestive system.
The four chambers of the ruminant animals are the reticulum, rumen, omasum, and abomasum, Rumen is the largest chamber and the most important part of the cows’ digestive system.
In the rumen, the various gas formation takes place. The involvement of the various hydrolytic species, fermentative species, and methanogen species together constitute the formation of methane gas along with the formation of carbon dioxide and hydrogen gas.
Microbial populations in the rumen also ferment the ingested forage and the water present there into Volatile fatty acids (VFA) that include acetic acid, butyric acid, and propanoic acid as the energy source for the body.
How does a cow produce methane gas?
When the cow ingests the forage, it gets passed through the esophagus towards the first chamber of the stomach which is the reticulum, where a small amount of digestion and absorption takes place.
Next, when the partly digested forage enters the rumen, then the Hydrolytic microbes there in the rumen break down the cellulose, hemicellulose, pectin, and starch content into soluble sugars (carbohydrates).
Further in the rumen, the various anaerobic bacteria also cause fermentation of the forage to form the Volatile fatty acids (VFA) that include acetic acid, butyric acid, and propanoic acid as the energy source for the body.
In the process of fermentation also called rumen fermentation, Carbon dioxide (CO2) and Hydrogen (H2) molecules are produced. During this process, a series of contractions of the rumen takes place while the ruminal pH is maintained over 5.8.
Next, the methanogens bacteria present in the rumen will cause the formation of methane (CH3) by reducing carbon dioxide to methane respectively.
So, methanogens play a vital ecological role in anaerobic environments by removing excess hydrogen and fermentation products produced by other forms of anaerobic respiration.
All of these gases viz. methane, hydrogen, carbon dioxide, and the Volatile fatty acids (VFA) that include acetic acid, butyric acid, and propanoic acid remain in the rumen, while the partially digested food moves towards the next chambers- omasum, and abomasum respectively.
Which metabolic process leads to the production of Methane in cows?
Enteric methane production is the metabolic digestive process that leads to the production of Methane in cows. All of these happens inside the rumen of the cow.
In this process actually, the carbohydrates (soluble sugars) are broken down by microorganisms anaerobically into simple molecules (VFAs) for absorption into the bloodstream of ruminant animals like cows.
Next, the methanogens react on the remaining carbon dioxide and hydrogen gas to produce methane.
The fermentation process leading to the production of VFAs is called enteric fermentation or rumen fermentation.
And, the whole process leading to the production of VFAs to methane gas formation is better called the enteric methane production process.
So, Enteric methane is one byproduct of this digestive process and is expelled by the animal through burping and a little also through farting.
While other by-products (acetate, propionate, and butyrate) which are the VFAs are absorbed by the animal and used as energy precursors to produce milk, meat, and wool in sheep.
Now, it is also to be noted that enteric methane production is directly related to the level of food intake, the type and quality of feed, the amount of energy consumed, animal size, growth rate, level of production, and environmental temperature as well.
It is also to be noted that, about 2% to 12% of a ruminant’s energy is typically lost through the Enteric fermentation process.
Are cows the largest source of methane?
No, cows alone are not the largest source of methane. However, the whole livestock that includes ruminant animals is the largest source of methane production from living biological world when seen on a global scale.
It is to be noted that, although the ruminants release methane into the atmosphere, but the huge amount of methane is actually released by human activities that are increasing the greenhouse gasses in the atmosphere.
Cows release methane into the atmosphere by burping or by farting or from the cow dung.
When all of the releases of methane from cows and other ruminants add together on a global large scale then it becomes a huge level of methane actually.
This release can actually cause a big impact on climate change by heating up the earth’s atmosphere due to the trapped sun’s radiation.
Today, scientists are concerned about the release of methane from ruminant animals like cows, sheep, etc.
Scientists are finding new ways to reduce the methane production from cows’ digestion by adding some supplements to their diet.
For example, scientists are trying by adding seaweed to the cows’ food hoping that seaweed can inhibit a specific enzyme that is involved in the production of methane while the cow digests its food.
However, it is also to be noted that the release of methane from ruminants is very very less as compared to the release of methane by other human activities when seen on a global scale.
How do cows pollute the air?
Agricultural livestock is responsible for almost a 14% increase in greenhouse gasses by releasing methane and carbon dioxide into the atmosphere by burping, farting, and breathing.
Methane is produced and is mostly responsible for global warming-related issues arising from agricultural livestock. Cows and other ruminants contribute mostly to it.
Yes, methane can cause pollution as it is a key precursor gas of the harmful air pollutant, the Ozone gas (O3). Meaning that, if the atmospheric methane level increases, then it will also cause an increase of Ozone (O3) in the atmosphere.
Ozone occurs both in the Earth’s upper atmosphere and at ground level. Ozone at the ground level is a harmful air pollutant, because of its effects on people and the environment and it can also cause difficulty in breathing and respiration.
Whereas the ozone on the upper atmosphere, which is also called the tropospheric ozone, is considered a greenhouse gas and may contribute to global warming enormously.
It is also to be noted that not only methane and carbon dioxide but also two-thirds of all ammonia comes from the cows in the form of excreted urine and feces.
Next, the urease which is an enzyme produced by microorganisms in feces can also react with the urea present in the urine to form ammonia.
Actually, the fact is that removing urea is a form of removing nitrogen from the cows’ body. So, cows do not directly excrete ammonia, and so it is only the excess dietary nitrogen (N) which is excreted as urea via. urine and feces.
Now, ammonia which is produced by cows and other agricultural livestock is considered a pollutant because it can cause soil acidification, direct toxic damage to leaves, and also by altering the susceptibility of plants to frost, drought, and pathogens.
Also, the gaseous ammonia reacts with other pollutants in the air to form fine particles of ammonium salts which can affect human and animal breathing as well.
How much methane do cows produce?
On an average, a single cow produces between 70 to 120 kg of methane gas per year.
So, it can be roughly estimated that the worldwide population of about 1.5 billion cows can easily produce about 105 billion kg to 180 billion kg of methane per year.
Thus, cows are the significant producers of methane, contributing about 35% to 37% of methane emissions resulting from human activity.
The livestock is responsible for releasing the methane gas equivalent to about 3.1 gigatonnes of carbon dioxide into the atmosphere annually.
That’s so much methane which is almost equivalent to 1,000,000,000,000 kg of carbon dioxide.
It is also to be noted that methane gas is about 23 times more powerful than carbon dioxide gas in terms of greenhouse gasses and its effect on the environment.
Comparing Cow vs. Car: An average cow produces enough methane per year to do the same greenhouse damage as four tons of Carbon dioxide does. On the other hand, the average car produces just 2.7 tons of methane per year.
It is also to be noted that about two-thirds of the total methane production by rumen fermentation is done by dairy cows.
