Study suggests inaccuracies in cattle methane estimates
20/12/2017
Methane gas comes from the microbial fermentation that occurs in animals’ stomachs, resulting in digestion-related (enteric) emissions, and from fermentation in their manure. But the total amount, argues lead author, Dr Alexander Hristov of the department of animal science at Pennsylvania State University, depends on the type of animal, what the animals eat and how their manure is stored.
He and his colleagues claim that cattle that mostly consume grain-based feed release significantly less enteric methane than cattle that graze on pasture. Current estimates of total livestock methane emissions may not fully consider feed intake and differences in animal diets, or the facilities used to store manure.
Dr Hristov and his colleagues analysed the feed intake data for cattle, as well as manure storage practices, in different parts of the US. Their resulting estimates for methane emissions varied widely from numbers currently reported by inventories such as the European Emission Database for Global Atmospheric Research (EDGAR).
For example, the researchers found that the combined enteric and manure methane emissions from livestock in Texas were 36% less than estimates by EDGAR. At the same time, their figures for emissions from cattle in California were substantially higher than EDGAR estimates.
Based on their data, the researchers say that results from studies that use “inaccurate distribution inventories to determine emissions sources” should be cautiously interpreted.
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