A scientist guides a tube into the mouth and down to the stomach of a two-month-old calf as part of a research project aiming to prevent cows from burping methane.

The ambitious University of California, Davis, experiment aims to develop a pill to transform cow gut bacteria so it emits less or no methane.

Cattle farming has become a major climate concern.

"Almost half of the increase in global temperature that we've had so far has been because of methane," said Ermias Kebreab, an animal science professor.

Methane, the second largest contributor to climate change after carbon dioxide, breaks down faster but is more potent. "Methane lives in the atmosphere for about 12 years" unlike carbon dioxide which persists for centuries, Kebreab said. "If you start reducing methane now, we can see the effect on the temperature very quickly."

Filho uses the tube to extract liquid from the calf's rumen - the first stomach compartment containing partially digested food.

Using the liquid, the scientists study the microbes that convert hydrogen into the methane that is burped out. A cow will burp 100 kilograms of the gas annually.

The calf and others receive a seaweed-supplemented diet to reduce methane production.

Scientists hope to achieve similar results by introducing genetically modified microbes that soak up hydrogen, starving methane-producing bacteria.

However, the team proceeds cautiously.

"We can't just simply remove" methane-making bacteria, as hydrogen could accumulate to the point of harming the cow, warned Matthias Hess, who runs the lab.

"Microbes are kind of social critters. They really like to live together," he said. "The way they affect each other impacts the overall function of the ecosystem."

Hess' students test different formulas in bioreactors, vessels that reproduce microorganisms' living conditions in a stomach from movements to temperature.

The project is being carried out at UC Davis as well as UC Berkeley's Innovative Genomics Institute.

IGI scientists are trying to identify the one microbe they hope to genetically alter to supplant methane-producing microbes.

The modified microorganisms will then be tested at UC Davis and in the animals.

"Not only are we trying to reduce methane emissions, but you also increase the feed efficiency," said Kebreab. "Hydrogen and methane are both energy, and so if you reduce that energy and redirect it to something else we have a better productivity and lower emissions at the same time."

The ultimate goal is a single-dose treatment administered early in life, since most cattle can't receive daily supplements.

The three research teams have been given US$70 million (HK$546 million) and seven years to achieve a breakthrough.

Kebreab pushes back against calls to reduce meat consumption.

While acknowledging this might work for healthy adults in developed nations, he pointed to countries like Indonesia, where it is seeking to increase meat and dairy production because 20 percent of children under five suffer from stunted growth.

"We can't tell them to not eat meat," he said.

AGENCE FRANCE-PRESSE

Scientists go with guts in search of way to stop cows burping methane