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Introduction
Global climate change has become a major cause of concern due to increase in atmospheric
concentrations of greenhouse gases (GHGs). Climate change affects animal production and well-
being, especially due to increase in ambient temperature. Methane is a potent GHG, emitted
as a result of enteric fermentation of feed by ruminants. Enteric fermentation is responsible for
about half of the total methane emission in India. Ruminant animals loose 4-12 per cent of
gross energy intake in the form of methane, which is not only detrimental to environment but
also results in energy loss to animals.
Methane production in ruminants
Ruminant livestock have a unique digestive system comprising of four stomach, which includes
the rumen, reticulum, omasum and abomasum. The rumen is the first and largest compartment
amounting to 80 per cent of the total stomach volume where microbes such as bacteria,
protozoa and fungi break down and ferment the feed material into products like volatile fatty
acids (VFAs), microbial protein, carbon dioxide
and methane.
Amongst the VFAs, acetate and butyrate are methanogenic and spare hydrogen during formation,
while propionate is glucogenic in nature and utilises hydrogen. More acetate and butyrate
production leads to production of more hydrogen and carbon dioxide, the main substrates
for methane production. Under anaerobic conditions of rumen, methanogenic bacteria utilise
hydrogen and carbon dioxide to form enteric methane, emitted mainly through belching.