Dung debate: Most methane from cows?

U. LEEDS (UK) — A compound in feces may be developed as a biomarker to estimate how much methane is produced by cows and other animals.

“When it comes to calculating carbon budgets there is currently a lot of uncertainty surrounding animal methane contributions, particularly from wild ruminants,” says Fiona Gill of the University of Leeds.

“We’re quite good at measuring man-made CO2 emissions, but techniques to measure the animal production of methane—a much more potent greenhouse gas—have serious limitations.

“If we can identify a simple biomarker for methane production in animal stools, then we can use this along with information on diet and animal population numbers to estimate their total contribution to global methane levels.”

The research is published in the journal Animal Feed Science and Technology.

Cows, sheep, and other ruminants are thought to be responsible for around one-fifth of global methane production but the precise amount has proved difficult to quantify. Methane production from animals is often measured using respiration chambers, which can be laborious and are unsuitable for grazing animals.

The compound, archaeol comes from organisms called archaea, which are symbiotic or ‘friendly’ microbes that live in the foregut of ruminant animals, producing methane as a by-product of their metabolism that is then released by the animal as burping and flatulence.

“We initially detected archaeol in the feces of several foregut fermenters including camels, cows, giraffes, sheep and llamas,” says Ian Bull of the University of Bristol. “We then expanded the study to evaluate the quantities of this compound in the feces of cows with different diets.

“Two groups of cows were fed on different diets and then their methane production and fecal archaeol concentration were measured.  The animals that were allowed to graze on as much silage as they wanted emitted significantly more methane and produced feces with higher concentrations of archaeol than those given a fixed amount of silage, supplemented by concentrate feed.

“This confirms that manipulating the diet of domestic livestock could also be an important way of controlling methane gas emissions.”

The research was funded by the Leverhulme Trust.

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