Methane is the carbon atom taking a detour

The methane debate is one of subtleties, with the true issue being the production of methane per kg of production.


We have to go back to the start to understand where methane fits in. Carbon atoms come down from the atmosphere into the paddock and then head off in all different directions. Some find their way back to the atmosphere quickly and some slowly. One path of the carbon atoms is into sheep and cattle.

After carbon flows into a cow to keep it functioning, some will end up part of the cow (18%), some will leave as carbon dioxide, some will leave as manure and some will leave as methane.

At any point in time, a percentage of the flowing carbon in a paddock will be returning to the atmosphere. Think of methane as part of this exit process.     

In the atmosphere, methane has to be converted back to carbon dioxide, before the carbon atom is ready to come down into the paddock again via plants.

Methane has a bad reputation because it is a greenhouse gas. However, when it is created in a cow, it represents energy lost. Energy that the cow had in its rumen (first stomach) that was not utilised for growth. Reinforcing the energy aspect of methane, it is a hydrocarbon gas that is the principal component of natural gas.

 

How methane breaks down in the atmosphere

 

The atmosphere is continuously producing what are known as hydroxyl radicals (OH). These OH radicals only last a very short period of time because when they come into contact with a methane molecule, they react with it to form carbon dioxide and water vapour. 

Methane is a short term gas. It lasts in the atmosphere for 8.7 – 12 years, depending on who you talk to.

There are a lot of feedback loops in natural systems that try to maintain stability. My understanding is that if the atmosphere warms, then methane will break down quicker.

 

How ruminant animals (sheep, cattle & goats) produce methane  

 

Ruminant animals produce a lot of hydrogen during digestion, which is removed by organisms called methanogens. They do this by combining the hydrogen with carbon dioxide to produce water and methane.


The rumen (first stomach), is a very complex internal ecosystem containing millions of micro-organisms that break down what the cow eats. It is a bit like a fermenting vat. Fermentation of plant material by these organisms allows ruminants to convert lower quality feed to energy more efficiently than monogastrics such as humans, birds and pigs.

The cow is relying on these micro-organisms to keep reproducing, and breaking down what it has eaten. It is when the micro-organisms reproduce slowly and empty the rumen slowly, that we have a problem with both livestock production and methane production.

Methane is lost energy for animal production

It has been known for many years that methane production represents poor conversion of pasture to energy and, as such, is a waste gas.

Put another way, if you increase the efficiency with which an animal digests its feed, you reduce the amount of energy released by the rumen micro-organisms in the form of methane gas, and instead the energy is channelled into growth.

Methane emissions and feed digestibility

“There is a relationship between methane emissions and feed digestibility; therefore, modifying the feed intake for digestibility will reduce methane emissions” (Dr Roger Hegarty).

Reducing methane relies on what the ruminant eats moving faster through the rumen. The speed of passage is determined by the carbon:nitrogen (C:N) ratio of the diet. In other words, the C:N ratio determines the digestibility of the feed.

It is lower nitrogen levels that cause the slower passage. Like all forms of life, rumen microbes rely on carbon as the main building block of their bodies, but they also have to source nitrogen, before they can break down what has been eaten. If there is not enough protein (nitrogen) in an animal’s diet, then the microbes reproduce slower. If the rumen microbes multiply slower, then the flow rate in the rumen is reduced. An earlier column linked increasing the “speed” of carbon to increased production, i.e. increasing the speed of carbon in the soil and in the ruminant increases profits.

When discussing pastures, some people think protein and some think nitrogen. To determine the protein content of pastures, just multiply measured nitrogen by 6.25.

A leaf has a higher nitrogen content than a stem, which is why it is more digestible.

Methane emissions per kilogram of production

Differences between production systems become clearer when the outputs are expressed as the amount of methane produced per kilogram of production. The faster the passage, the less methane produced per kg of production.

Lower quality diets actually produce less methane per day, because less is happening in the rumen, but this is not the point. Animals on low quality diets produce more methane in total by the time they get to the meatworks. This is because it takes them longer to achieve the same level of production. The key to reducing total methane of slaughter animals is getting them to the meatworks quicker.

During drought is when methane emissions per kilogram of production are at their highest. This is when fodder trees and saltbush plantations can supply a protein source to improve the digestibility of the total diet.

To reduce methane production from breeders, graziers need to achieve higher reproduction rates, i.e. fewer breeders for the same natural increase.

Linking methane emissions to profit

Putting the methane issue into commercial perspective, it has been suggested that a 1% increase in production through a superior diet results in a 1% reduction in methane. The difference in methane production between grazing systems can be substantial. The level of methane produced is another example of the general principle that the greenhouse outcomes of agriculture are a reflection of economic efficiency.

Conclusion

What you, as a producer, make available for the sheep and cattle to eat determines the amount of methane they produce. This is why good management of carbon flows after rain is so important to increase digestibility of the pasture.

The major strategy for reducing methane production will be the same as the key driver for profitability in grazing: reducing the number of grazing days per kilo of product.

The key to reducing methane production is to reduce the time feed spends in the rumen with the methogenic bugs. A diet with a high C:N ratio will spend longer in the rumen and generate more methane than a diet with adequate protein.

It is improving the digestibility of the diet that is the cornerstone of reducing methane produced per kg of production.

Next week’s discussion:   “The Carbon Grazing principle relates to management of carbon flows”

Alan Lauder