Above: The sulfur hexafluoride tracer technique allows scientists to measure the amount of methane emitted from the animal’s mouth and nose. Photo credit: Nicolas DiLorenzo

When you first learn that cows produce methane, a greenhouse gas, you might assume it comes from the animal’s rear end. But you would be wrong.

“Methane is generated in an organ called the rumen, which is the first of the cow’s ‘four stomachs,’” said Nicolas DiLorenzo, a researcher at the University of Florida who studies methane production in cattle. “The rumen is quite close to the cow’s mouth, so the mouth is the closest exit. This is why the cow releases this methane by burping.”

This anatomic fact is the whole reason why scientists like DiLorenzo study the rumen — and why DiLorenzo is often correcting the misconception that cow flatulence is the source of methane.

“When it comes to greenhouse gas emissions from cattle, we go to the source, and that is the rumen,” DiLorenzo said.

For several decades, researchers have been looking for ways to reduce the methane produced in the rumen. Now new research by DiLorenzo and others shows that a small change to cattle’s diets reduced the animals’ methane emissions by 11%. These findings are a step toward reducing greenhouse gas emissions from livestock.

The study was led by UF/IFAS College of Agricultural and Life Sciences graduate Darren Henry, now an assistant professor in the department of animal and food sciences at Texas Tech University. The study was part of Henry’s doctoral research directed by DiLorenzo and received funding support from the National Institute of Food and Agriculture.

The study’s authors discovered that cattle produced less methane when a supplement commonly given to grass-fed cattle was replaced with a supplement that provided the same nutrition but had different chemical properties.

To understand why, you need to know how the rumen works.

“The rumen is where bacteria ferment the food the cow eats, helping break it down and allowing the cow to absorb more energy and nutrients from the food,” said DiLorenzo, one of the study’s authors and an associate professor of animal sciences at the UF/IFAS North Florida Research and Education Center.

“I tell my students that the rumen is ‘the animal within the animal’ because it has a kind of life of its own,” he added.

The rumen is also where methane enters the equation. As bacteria ferment the cow’s food, some microorganisms create methane as a byproduct. Eventually, the cow burps, and methane enters the atmosphere.

Previous research has indicated that nitrates interrupt the chemical reactions that allow methanogens — microorganisms in the rumen responsible for methane — to produce methane. The UF researchers wanted to test if feeding nitrates to cattle would have the same effect. In the experiment, they introduced nitrates by swapping out urea for encapsulated calcium-ammonium nitrate (eCAN).

“Diets of grass-fed cattle are often deficient in protein, so urea is used to supplement protein,” DiLorenzo said. “The thinking was: What if we used a different substance that would provide protein like urea does but had properties that would affect methane production?”

The researchers fed eCAN to cattle by mixing it into molasses, a traditional vehicle for urea. Cattle will lick up every drop of molasses presented to them, so this method ensured they would consume the eCAN the researchers provided.

“The eCAN looks like Dippin’ Dots ice cream and allow for the slow release of the calcium-ammonium nitrate in the rumen,” DiLorenzo said.

To measure how much methane the cattle produced when fed eCAN, the researchers used something called the sulfur hexafluoride tracer technique. This technique uses a U-shaped canister attached to a halter on the cow’s head. Small tubes connected to the canister sit above the cow’s nostrils. The device allows scientists to measure the amount of methane emitted from the animal’s mouth and nose. Compared with cattle that were given urea, cattle that consumed eCAN produced 11% less methane.

“This is quite a large reduction and an exciting result,” DiLorenzo said.

The study is published in “Journal of Animal Science.”

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