12. Enteric Methane Emission Under Different Feeding Systems

Methane is a potent greenhouse gas (GHG) which is responsible for global warming, and it is about 23 times more potent than carbon dioxide and is produced worldwide by biotic and anthropogenic activity. Increased industrialisation in the past few decades and an increase in global human population have increased the demand of food particularly of animal origin to a significant level. The livestock population, especially ruminants in particular, is responsible for emitting 16–20 % of the CH₄ to the atmosphere. The enteric fermentation in ruminants is unique, carried out by the anaerobic microorganism, and culminates in the formation of CH₄, which is the sink for hydrogen and carbon dioxide, formed as a result of anaerobic fermentation in the rumen. The population of domesticated ruminant livestock species like cattle, buffalos, sheep, goat, mithun, yak, etc., which provide food to humans has increased worldwide in the recent past. These livestock are reared under different systems that are prevailing in a particular country, and the most common identified livestock rearing systems are intensive, extensive and semi-intensive. In intensive system of rearing, the animals are confined and more concentrates are fed with provision of quality roughages. While in the extensive system of rearing, the livestock are let loose and depend on the pasture for their growth and production, and the quality of the pasture is responsible for the nutrients assimilated by the animal. The semi-intensive system of rearing is a combination of the above two systems. Enteric CH₄ production in ruminants depends on several factors like type and quality of feed, the physical and chemical characteristics of the feed, species of livestock, feeding level and schedule, the efficiency of feed conversion to livestock products, the use of feed additives to support production efficiency, the activity and health of the animal and genetic make-up of the animal. Therefore, feeding system(s) employed for livestock rearing certainly has an effect on the enteric CH₄ production. A concerted effort has been put in this chapter to get an insight into the different livestock rearing and feeding systems, CH₄ contribution from livestock and global warming, CH₄ production from different feeding systems and means to augment livestock production by reducing enteric CH₄ under different feeding regimens.