Methane arising from the enteric fermentation in ruminants is one of the major greenhouse gases (GHGs) and a key component as far as agricultural emission is concerned. Relative high global warming potential and biological energy loss from animal system makes methane (CH4) much more important than any other GHG. Researchers worldwide have attempted many approaches with variable success for enteric methane mitigation and the search for advanced sustainable approach is still on. However, attempting mitigation without knowing the precise emission from a country is not going to serve any purpose. Most of the countries, especially developing nations, are still lacking a valid database for enteric methane emission. In order to arrive at a national methane emission figure, a country should have proper methodologies for estimating the methane emission from different ruminant species fed on various dietary combinations as per local and seasonal availability. As sheep are being maintained by small and marginal farmers, therefore, the loss of biological energy in the form of CH4 under the resource-deficit scenario of farmers make this species as equally important as cattle and buffaloes. This chapter describes various methodologies which can be employed for the direct or indirect estimation of CH4 emission from sheep. Each methodology has been discussed in the chapter at length along with their advantages and limitations. Though the adoption of a methodology for the estimation of CH4 depends on many factors, in vivo techniques such as GreenFeed, sulfur hexafluoride tracer technique and respiration chambers are instrumental in order to estimate the precise emission and could be useful in determining the national CH4 emission when a large number of experiments are conducted involving large animals and locally available seasonal feedstuffs with repeated measurements.
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