• Jin Gan

Methane Emissions by Dairy Cows And How To Reduce It


Methane Emissions By Dairy Cows

Methane As A Greenhouse Gas

Methane is an important greenhouse gas whose concentration in our atmosphere has more than doubled compared to pre-industrial times. Compared to carbon dioxide, methane is a more potent greenhouse gas. However, due to its shorter atmospheric lifetime of around 12 years, the global emissions would only need to be reduced by about 8% from current levels to stabilise the methane concentration at today's level.

Methane Production And The Dairy Cow

Agriculture in the United States contributes approximately 6 - 7% of the total U.S greenhouse gas emissions. The main sources of methane emitted comes from enteric (microbial) fermentation, which represents approximately 20% while manure management represents about 7%. Ruminants such as dairy cows, goats and sheep are the main contributors to methane production.

How Does Cow Produces Methane Gas

To understand why is it that cows produce methane gas, it is important to know a little more about how they work. Ruminants such as cows, goats and sheep have four stomachs. They digest the food in their stomach rather than the intestine, as humans do. Ruminants eat food, regurgitate it as cud and eat it again. The stomach of a ruminant is filled with bacteria which helps in digestion. However, they also produce methane gas.

Why Do Cows And Other Ruminants Produce Methane?

Since the mid-20th century, due to the development of large scale agriculture, farming has since became a very lucrative business. Smaller farms are then consolidated into larger farms which are then run by large corporations.

At the start, grazing areas were filled with many different types of grasses and flowers that grew naturally. This offers the cows and ruminants a diverse diet. However, these grasses and flowers were not the most efficient in terms of feeding many cows in a short period of time. Corporations that wanted to maximise profits are looking for ways to improve the efficiency in feeding. Hence, many of the grasses and flowers that were grown naturally became reseeded with perennial ryegrass. With the aid of artificial fertilisers, this allowed the ryegrass to grow quickly and in huge quantities and thus able to feed many cows. With that being said, the drawback is that these ryegrass lacks the nutritional content of the other grasses and prevents other more nutritious plants from growing. Although ryegrass allows many cows to be fed efficiently, it inhibits digestion. Due to the difficulty of digesting, the grass ferments in the cows' stomachs, where it interacts with microbes and produce gas. The exact details of the process is still being studied which will allow scientists to come up with solutions to reduce methane emitted by cows.

Based on EPA reports, Inventory of US Greenhouse Gas Emissions and Sinks: 1990-2004, beef cattle remain the largest contributor of methane emissions, accounting for 71% in 2004. Dairy cattle on the other hand accounted for 24% and the rest were from horses, sheep, swine and goats. In general, the methane emission is trending downwards due to the decreasing population of both beef and dairy cattle and improved feed quality for feed lot cattle.

How To Reduce Methane Emissions From Cows

There has been many research conducted especially in Canada, United States and Europe on ways to reduce methane emissions by cows. The main focus is on nutritional strategies, especially cows grazing pasture.

Some of the dietary practices that have been shown to help reduce the methane emissions include the addition of ionophores, fats, the use of high quality forages, and the increase use of grains. These methods used will help reduce the methane emitted by cows through manipulating the ruminal fermentation, direct inhibition of the methanogens and protozoa, or by a redirection of hydrogen ions away from the methanogens.

There are a few relatively new mitigation options that is being investigated. This include the addition of additives such as probiotics, acetogens, bacteriocins, organic acids and plant extracts. As for long term approach, there is a possibility that genetic selection of cows that have improved feed efficiency can help reduce methane emission. Here are more information about some of the methods that are able to reduce methane emission:

  1. Increasing the feed efficiency of cows can help to reduce methane emissions. One of the ways to improve feed efficiency is to feed the cows high quality and highly digestible forages of grains. With that being said, the emissions emitted in producing or transporting the forages and grains should be taken into account,

  2. The use of rumen modifiers such as ionophores can help improve the dry matter intake efficiency, as well as suppressing the acetate production. This will reduce the hydrogen released. Studies have shown that the methane emission has been reduced by 10%. However, the results is not consistent. More research have to be done on the use of ionophores to help reduce methane emission.

  3. It is possible to reduce the emissions by 40% through grinding and pelleting of forages. With that being said, the costs associated with it could be very high.

  4. Studies have shown that dietary fats has the potential to reduce methane up to 37%. This is through biohydration of unsaturated fatty acids, enhanced propionic acid production, and protozoal inhibition. However, the effects are variable and there is a possibility that lipid toxicity to the rumen microbes can cause problem. This method can affect the milk components negatively and thus reduce the income for farmers.

  5. Having good management practices that are able to reduce the number of cows while maintaining the same output can reduce methane production. For example, by improving the rate of reproduction of cows, this will lead to fewer replacement heifers, and hence reduced methane emissions.

There are a few more interesting ways to help reduce methane emission but they are not very practical at this moment in time. One good example would be the defaunation of rumen. Removing the protozoa has been demonstrated to reduce the methane gas emission up to 20%. There are also other examples such as encouraging acetogenic bacteria to grow in order to perform the function of removing hydrogen instead of methanogens. The acetogens convert the carbon dioxide and hydrogen to acetate. This would allow the animal to use it as a source of energy. In recent times, scientists are also developing a vaccine, which will help stimulate antibodies in the animal that are active in the rumen against methanogens.

Although the ideas suggested above could potentially work, they are potential toxicity to the rumen microbes and the animal, short-lived effects due to microbial adaption, volatility, expense, and a delivery system of these additives to cows on pasture.

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