The greenhouse effect is solar absorption of infrared radiation both by earths surface and by atmospheric gases, which resultantly are heated, reemitting low frequency infrared radiation with a high absorptive power. This changes climate which includes prolonged periods of excessively high temperature, heavy rains increased wildfires, permafrost thawing, severe droughts, sea-level rise and ocean acidification. This change affects ecosystems, natural resources, communities, economies and public health across the nation. The global greenhouse gases (GHS) emission is rising that is resulting into inevitable global warming. The most important gas associated with global warming is CO2 but other GHS, such as CH4, N2O, ozone and sulphur hexafluoride also contribute to this global warming.

Changes in atmospheric GHS concentrations, solar radiations, aerosols or suspended particles (Solid/Liquid) in air modify climate system energy balance. The CO2, CH4, N2O and halocarbons are long-lived GHS and their concentration is continuously increasing because of human activities.

The United Nations intergovernmental panel on climate change (IPCC) estimated that global temperature would rise between 1.1 and 6.40C by the end of this century. The 6.40C rise or close to it is catastrophic. The rise in sea level can devastate low-lying global countries and coastal communities. More than half of Asia harbors about 87 per cent of worlds known 400 million small farms and they live near coastlines and are directly vulnerable to rises in sea level. This huge population is vulnerable to climate change because its reliance is on regular rainfall. An increase of just one degree Celsius in night time temperatures during the growing season will reduce cereal yield by more than 10 per cent.

This global warming will reverse social and economic progress made so far and can cause food shortage through severely affecting agriculture and livestock. The poverty stricken people/nations will be more vulnerable.

According to United Nations IPCC, nearly 80 per cent of total worlds power could go green — run on renewable sources — by the end of 2050. In the year 2008 and 2009, 300 Gigawatts (GW) of new power was added globally and 140 GW was from green sources. In 2009, wind power, hydropower, grid-connected photovoltaic, geothermal and solar water heating grew 30, 3, 50, 4, and 20 per cent, respectively. More than 50 per cent of the global green energy capacity is in developing countries and China being on the top of list.

According to an estimate, Agriculture contributes 14 per cent of globes GHS. The 40 per cent agricultural output global value comes from the livestock sector and support about one billion peoples livelihood and food security. Demand for animals and animal products are constantly increasing with growing global population. When quality food demand rises, it increases the demand for animal protein including eggs and meat.

Livestock sector is going through a complex technical and geographical change process. It is shifting the balance of environmental problems caused by the sector. According to the FAO, agricultural CH4 output could increase 60 per cent by 2030. Globally, 1.5 billion cows and billions of other grazing animals emit dozens of polluting gases, including huge quantity of CH4. The 2/3rd of all NH3 comes from cows. Cows emit a massive amount of CH4 through belching, with a lesser amount through flatulence.

Statistics vary regarding how much CH4 on an average a cow expels. A mature cow or buffalo can emit 100 – 200 liters of CH4 daily. Some researchers have reported that CH4 emissions can increase up to 500 liters. This emission is comparatively more than the pollution produced by a single car daily.

According to FAO, CH4 emitted from livestock every year was equivalent to around 144 million tons of oil, enough to power the whole of South Africa. Over a 100-year period, CH4 has at least 25 times the global warming potential of CO2.

One may need to understand why do ruminants produce CH4? This will help understand easily if one can know a little about how they digest their feed. Cows, Buffaloes sheep, goats and several other such animals belong to a class of animals called ruminants. They are called ruminant because they possess fore-stomach, consisting of rumen, reticulum and omasum.

The feed of these ruminant animals is generally fibre based. These ruminants digest their feeds in their fore-stomachs. Ruminants eat their feeds, ruminate it and regurgitate it as cud and eat it again. This fore-stomach is stacked with microflora which aid in digestion and during this feed degradation, many products, including amino acids, volatile fatty acids (VFA), NH3, CH4, etc. are formed.

The 80-95 per cent CH4 generated during ruminants digestive process is mainly expelled via eructation through the mouth and nose. Ruminal microbial activity hydrolyses dietary organic matter to amino acids, NH3, VFA and simple sugars. The methanogens or CH4 producing bacterial species are commonly responsible for regulating the overall rumen fermentation. In rumen anaerobic (oxygen deficient) environment methanogens remove H2 by reducing CO2 to produce CH4.

Microbial fermentation of carbohydrates results in the production of VFA, mainly butyric, acetic and propionic acids, CO2 and H2. The VFA can provide up to 80 per cent of the total energy requirements of the animal. In general, synthesis of butyric and acetic acid in rumen generates higher quantities of H2 and CO2. High forage diets yield more acetic acid. Its production level drops if there is a lack of effective fiber in the diet. Feeding high concentrate diet, pelleting, steam flaking or crimping and inclusion of oil in ration can reduce production of acetic acid and increases propionic acid. Butyric acid provides energy to the rumen walls.

The authors (a) Tamgha-i-Imtiaz is the OSU Distinguished Alumnus, distinguished national professor and (b) is Izaz-i-Fazeelat, Institute of Animal Nutrition and Feed Technology, University of Agriculture, Faisalabad.

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