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The US Environmental Protection Agency (EPA) released the Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2012 report, released on April 15, 2014 stating “beef and dairy cattle are by far the largest emitters of methane gas”. 14% of the greenhouse gas emission comes from cattle, due to their large population and particular digestive system characteristics they are account for the majority of methane emissions. This makes them the 3rd largest global greenhouse gas producers.

Cattle are ruminant animals that acquires nutrients from plant-based foods by a fermentation process. The bacterial process of breaking down the nutrients requires the fermented ingesta (known as cud) to be regurgitated and chewed again. A ruminant’s stomach consists four compartments: the rumen, reticulum, omasum and abmasum. The micro-bacteria found in rumen, called methanogens, are active during enteric fermentation process and it produces methane by-product which is exhaled by the animal.

Canada, Australia, and New Zealand has all taken initiative to conduct scientific research and strategies on effective ways to reduce greenhouse gas emissions from cattle. Reducing the amount of methane and nitro oxide gases can be achieved by altering and reducing the microbial population in the rumen that is present during the enteric fermentation process. The Canadian Agriculture ministry and Agri-Food Canada (AAFC) established a timeline for development of methods of reducing methane emissions from cattle (figure 1) [2]. The most immediate and effective way is by changing the cattle’s diet and feeding strategy. The most immediate and effective way is by changing the cattle’s diet and feeding practices. Breaking down the feed for cattle by grinding and pelleting forages increases the passage rate. Feeding cattle easily digestible carbohydrate rich diets (grain and corn) and better quality feed can increase animal performance without high intake Introducing and increasing dietary oils like crushed oilseeds (sunflower seed, canola seed, flaxseeds), and plant extracts can reduce methane up to 20%. The most effective method reduce methane emissions from cattle is a combination of grain based diets with oil feed additives. Reducing the numbers of animals also help reduce methane production.

Feeding Strategies
Aside from the natural process of cattle’s digestive systems, the quality of the animal’s feed and feed intake also has a direct affect on methane emissions. Low quality feed and/or high feed intake leads to higher methane emissions. Methane production increases as the animal eats more feed, improving feed energy conversion. The mount of feed consumed per kilogram of milf produced or weight gained, decreased methane output. Beef and diary cattle are the largest contributor of methane, from enteric fermentation, accounting for 96% of total emissions in agriculture [1]. Cellulose-rich diets (grass and hay) composes most of cattle diets, however it takes longer process of digestion resulting high methane production from the rumen that would be exhaled by the animal. From the EPA report beef and diary cattle produce a cumulative 135.6 Tg CO2 Eq (1.4 billion metric tones) of methane from enteric fermentation (figure 2) [1]. Changing to a grain based diet that is carbohydrate-rich diets can reduce methane gas by 20% because the feed is highly digestible for cattle. Breaking down the feed by grinding and pelleting of forages increases the passage rate of the cattle digestive system therefore reducing methane emissions by the animal. Some argue that a change in diet will impact on the quality of milk and meat, however diets based on corn grain, barely grain, corn silage and alfalfa reduce methane emissions and it still maintains the high quality of milk and meat. An article written by Mandi Jones for the University of Nebraska-Lincoln states Grain also does increases the level of feed conversion efficiency making cattle more energy efficient, increase of performance, and increase of profitability (figure 3) [3]. Introducing fat additives are high energy sources that can reduce methane by decreasing fermentation activity in the rumen. High quality and digestible feed also decreases the overall waste excreted from the animal and lower nitrous oxide and methane emissions levels from manure [6].

Feeding Additives
The National Livestock Methane Program in Australia reported that feeds containing tannin or high levels of oil reduce methane production from livestock. Oil supplementation and tannin reduces methane by reducing fibre digestion in digestive track, suppressing the micro bacteria found in the rumen that produces methane. The Carbon Farming Initiative states that “every 1% extra oil added to the diet of livestock, enteric methane can be reduced by3.5%” [4]. Adding oils into the cattle diets not only reduce emissions up to 20%, but it also increases energy and performance of the animal by increasing milk production for diary cattle. Dietary fats could be found in crushed oil seeds like sunflower seed, canola seed or flax seeds. It could also be found in other agricultural by-products. Whole cotton seed, cold-pressed canola meal, hominy mean and brewers grain, all could reduce enteric methane. However the most effective additive game marc, the by-product of wine making with a high concentration of both fat and tannins. Integrating grape marc into the feed for cattle can reduce methane by 20% alone [4].

In a recent study the Canadian APCC supplemented the cattle diet with commercial active dried yeast products and it proves its ability to improve fibre digestion in the rumen. This not only improves the cattle’s digestion but also by 6% [2]. Enhancing the feeds can provide only short term solution however Australia and New Zealand has research teams exploring innovative ways of eliminating the microbes in the rumen that produce methane, such as vaccines.

Manure Management
Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990–2012, reported treatment, storage, and transportation of live stock manure can produce anthroogenic methane and nitrous oxide emissions and a cause of greenhouse gases, water, and land contamination. In 2012, total of nitrous oxide and methane missions from manure management were estimated 80 Tg C02 Eq (80 million metric tons) from cattle . Year by year there is an increase of emissions. There are 2 pathways for Indirect nitrous oxide emissions. First volatilization of gases from the animal’s manure. Second, manure runoff and leaching to the soil, ground water, streams, and rivers. When livestock manure is stored or treated in systems in anaerobic conditions for fertilizer or later usages, it increases the production of methane gases. “When manure is handled as a solid or deposited on pasture, range, or paddock lands, it tends to decompose aerobically and produce little methane”. However the concentration of cattle populations in certain areas of the country and the number of animals in each facility, manure has to be transported which ultimately.

Reducing the Number of Cattle
Meat and diary production has shown a large stress on the environment, not only through methane but also fossil fuels, water and land consumption, loss of biodiversity. Methane emissions could be simply reduced by the number of cattle.