A peacefully grazing herd of cattle doesn't tend to conjure up visions of global warming, but the environment, the producer's bottom line and the animals all could benefit if cattle produced less methane.

Methane is the second-most abundant greenhouse gas. The world's agricultural livestock produce about 17 percent of the methane in the atmosphere. A byproduct of digestion, cattle and other ruminant animals produce methane when organisms in their stomachs called methanogens break down fiber in grasses and grains they eat.

It's a waste of feed and energy, said Steve Ragsdale, a University of Nebraska Institute of Agriculture and Natural Resources biochemist.

"From 5 to 15 percent of the digestible energy in feed is lost as methane gas," Ragsdale said. "Animal scientists have thought for 50 years that if we could reduce the amount of methane produced by cattle we could significantly reduce the amount of feed they need."

Ragsdale, Animal Scientist Jess Miner and UNL Chemist James Takacs think they've found a way to do just that: cut the amount of methane cattle produce during digestion while boosting the amount of acetate, a compound the animal uses for energy. The result would be less atmospheric methane, less feed required and more dollars in producers' pockets.

The team has designed chemical compounds that inhibit a key enzyme in methane production. When the enzyme is stopped, so is methane production. Takacs' lab has synthesized about 100 compounds that are potential inhibitors. Ragsdale tests them in methanogen cultures in his lab to see whether they block methane production. They have found four classes of compounds that inhibit the enzyme.

But will they work in a cow?

"It's one thing to block methane in a monoculture in the lab, but it's a difficult challenge to block methane in a complex ecosystem like the rumen," Miner said.

The rumen is the first compartment in a cow's three-part stomach, where more than 100 billion microbes – bacteria and methanogens – live in each milliliter of rumen fluid. When feed enters the rumen, microbes break down the fiber and produce compounds the animal needs for energy, such as acetate, and byproducts, such as methane.

To test whether the enzyme inhibitors will block methane in the rumen, Miner uses an "artificial rumen," a glass vial filled with a cloudy, microbe-rich liquid that mimics rumen fluid.

"We take the inhibitors that look promising in Ragsdale's cultures and evaluate them in the artificial rumen," Miner said. "Some compounds that work in culture don't work in the rumen – but some do work."

The team is working to lower the concentration of inhibitor needed to block methane production. The present concentration is too high to test on cattle, but Ragsdale is confident that a useable product is on the horizon. The university has patented the team's enzyme inhibitor process.

"An important advantage of our inhibitors is that they only work on methanogens and don't affect other microbes in the rumen," Ragsdale said. This leaves the bacteria free to produce more acetate to provide energy for the animal, which reduces feed requirements. Inhibiting methane could cut feed requirements as much as 30 percent.

A feed additive containing the methane inhibitor would provide an economic benefit to producers, but Ragsdale feels the greatest benefit would be the positive effect on global warming.

"Based on methane's contribution to greenhouse gases, I believe that a 50 percent reduction of the methane produced by livestock would mitigate global warming," he said.

The team is working with Restoragen, a Nebraska-based private company, to commercialize the methane inhibitors with funding from a National Institutes of Health small business grant.

– Monica Norby

A team of NU researchers has designed chemical compounds that inhibit a key enzyme in methane production. Above: Biochemist Steve Ragsdale pours liquid nitrogen into a high resolution spectrometer his team uses to study potential methane-blocking enzymes.

Animal Scientist Jess Miner and Melody Nelms, an undergraduate research assistant, examine a container of rumen fluid in his lab. Minor takes inhibitors that look promising in Ragsdale's cultures and evaluates them in an artificial rumen.

Bree DeMontigny, a graduate research assistant in animal science, places rumen samples in vials that serve as artificial rumens. Samples are incubated for 30 hours to allow methane to form. The artificial rumens allow researchers to assess how well methane-blocking compounds developed by an interdisciplinary university team might perform in a real cow's rumen.