Cow methane proof 'is in the pat'

Cow pat and boot The discovery is one step toward quantifying animals' contributions to greenhouse gases

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Research suggests the amount of methane that ruminants such as cows produce is correlated to quantities of a molecule in their faeces called archaeol.

Methane production by ruminants is a large unknown, and is relevant in climate science as it is a powerful greenhouse gas.

Current methane measurement methods are labour-intensive or invasive.

The new work, in Animal Feed Science and Technology, could more simply measure both wild and farmed animals.

Archaeol is a well-studied molecule found in the cell membranes of primitive single-celled organisms that live in the guts of ruminants such as cows, aiding their digestion and in the process producing methane.

"Archaeol has been measured in all kinds of different [contexts] and used for different purposes, but as far as we're aware this is the first time it's been correlated with estimates of methane emissions," said Fiona Gill, lead author of the research who is now based at the University of Leeds.

In a relatively small study, Dr Gill and her colleagues fed 12 bulls two different diets, one composed of grass and one of concentrated feed, measuring both the amount of archaeol in the animals' faeces and the amount of methane they produced.

To date, methane measurement methods have involved sealed chambers in which animals' consumption and production of gases are carefully measured, or by using sources of a gas called sulphur hexafluoride placed in the animals' stomachs whose output can be measured.

Wild ambitions

Both are involved processes that do not lend themselves to widespread use, or to any use with wild, roaming animals. But the team found a suggestive correlation between feed stock, archaeol concentrations, and methane production that could simplify matters.

"There is clearly a strong relationship between the higher methane production on the silage diet, which corresponds to higher faecal archaeol concentrations," Dr Gill told BBC News.

"So there's a general correlation between methane emissions and faecal archaeol concentrations."

Dr Gill stressed that larger studies will be needed to pin down a more precise functional relationship between the two. But because methane is a greenhouse gas more than 20 times more potent than carbon dioxide, such precise numbers will be of great use.

"There definitely is a need for better estimates of methane emissions from animals," she said.

"In the (International Panel on Climate Change) report, the contributions from various methane sources are quite poorly known; while the overall amount of global methane is quite well constrained... there is a need for a method to better estimate the contribution of ruminants and in particular the contribution from wild animals."

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