Agriculture is responsible for approximately 10% - 12% of global anthropogenic greenhouse gases (GHG)
emissions, excluding land use change [1] [2], particularly livestock is increasingly recognized as both a potential
victim of it [3] [4]. Livestock is assumed to be responsible for the largest part at nearly 80% of total agricultural
GHG emissions. This is particularly due to methane (CH4) emissions from enteric fermentation and manure
handling [5]-[7].
Methane is the major GHG produced from enteric fermentation during the normal digestive process of ruminants [8] [9]. It is important to note that production of greenhouse gases from animals and their impact on climate changes are a major concern worldwide [10] [11]. Production of GHG is often recalculated to production
of carbon dioxide (CO2) as carbon dioxide equivalent (CO2-eq), converted amounts of other gases to the equivalent amount of carbon dioxide with the same global warming potential. Cattle are considered to cause an increase
in emissions with about 4.6 Gt (gigatonnes) of CO2-eq, representing 65% of sector emissions. Average emission
intensities are 2.8 kg CO2-eq per kg of fat and protein corrected milk 12 for milk and 46.2 kg CO2-eq per kg of
carcass weight for beef [12]. However, the current review will be devoted especially only to methane emissions