CLEAR Conversations: Inside a Researcher's Mission to Understand Methane
At the UC Davis CLEAR Center, researchers spend their days asking a big question: how can we raise livestock in ways that are more climate-friendly? For PhD candidate Conor McCabe, now approaching the end of his time in the Mitloehner Lab, that question has fueled not just one research project, but a career full of early mornings, and a huge scientific effort that spans animals, microbes, and emissions.
McCabe didn’t start out as a dairy kid. He grew up on a small farm in Oregon—“pretty much an Old McDonald’s farm,” he jokes—with pigs, cattle, pumpkins, and Christmas trees. His mother once served as a dairy princess, but dairy cattle weren’t part of Connor’s life until college. After studying animal science at Cornell, Purdue, and now UC Davis, he’s seen “different pockets of cows across the country,” as he puts it. But it wasn’t until arriving at Davis that he found the right intersection of ruminant biology and real-world impact.
“Sustainability is one of the hottest topics right now,” he said. “And no two dairy farms are the same so there are a lot of opportunities there.”
He added with a laugh, “Plus I really enjoy cheese, butter and ice cream."
To understand McCabe’s research, it helps to understand the animals themselves—ruminants like cattle, sheep, and goats that evolved with a four-chambered stomach. Their digestive superpower? Turning fibrous, human-inedible plants into nutrient-dense food.
"And so I wanted to pursue this pathway and think about what are some real opportunities and how do we continue to have animals part of food system sustainability solutions," McCabe said.
What makes ruminants remarkable also makes them methane emitters. Microbes inside the rumen break down fiber through fermentation, and methane is an unavoidable byproduct.
“The trick,” McCabe said, “is balancing what cattle need and how they evolved to digest feed, with the need to reduce methane at the same time.”
That balance has led researchers worldwide to explore feed additives which are small supplements mixed into a cow’s feed that can disrupt methane-producing pathways in the gut.
McCabe describes a cow’s diet as a casserole: hay and byproducts all mixed together so each bite contains everything the animal needs. Feed additives act like the spices sprinkled in before the dish goes in the oven. And while they might be tiny in size, feed additives have the potential to have a big impact in ruminant animals.
“These additives can either inhibit the pathways or the enzymes responsible for methane formation, or make conditions less favorable for methane to form in the first place,” he explained.
His team is testing one of the most promising compounds: 3-nitrooxypropanol, or 3-NOP is a molecule already approved in multiple countries and making its way into commercial use.
The UC Davis CLEAR Center project is ambitious: 66 dairy cows, nearly two-thirds of the entire campus herd. Every single cow is fed twice a day, every day, using diets mixed precisely to include 3-NOP at just the right concentration. The study will take place for a full lactation period of a dairy cow.
“The digestive system of a cow has never seen something like this for such a long time,” McCabe said. “So we’re asking: do emissions look the same on day one as they do on day 500? Can microbes adapt around this stressor over time?”
It’s a critical question. If 3-NOP is going to support long-term methane reductions across dairy supply chains, it must remain effective year after year and not just during a short research window.
Alongside methane data, the team monitors feed intake, milk production, animal health, and even changes in the microbiome.
He added that,” It’s been exciting to be part of, to help set up and to see the results when they finally are released.”
When it comes to feeding the cows, “they eat approximately 100-110 pounds of food per day,” and the 3NOP is a small portion of that, one that McCabe notes is “hard for them to sniff out,” and possibly reject. But what helps is that the additive is mixed into the feed or “casserole” so the hope is that “they’re getting a little bit of the additive in each bite.”
How Do You Measure a Burp?
One of the first questions undergraduates ask is how methane is actually measured.
UC Davis uses GreenFeed units, machines McCabe describes as “basically breathalyzers for cows.” The cows are trained to walk up to the machine, which reads an ear tag, dispenses a small treat, and measures the gases the cow exhales while eating.
“They don’t know their emissions are being sampled,” he said. “They just think it’s a candy machine.”
Because emissions vary throughout the day (usually lower overnight and higher after meals) the cows visit the machines multiple times, giving researchers a detailed picture of methane patterns.
But feed additives do have a downside being they have to be provided every day. But as McCabe notes, they still hold considerable promise because they integrate naturally into routines farmers already have in place.
The Human Side of the Work
Behind the science is a pretty grueling daily routine. During the study’s most intense phases, McCabe’s world narrowed to the dairy, the lab, and the grocery store.
“We start when the cows start being milked at 4 a.m.,” he said. “Feeding takes three or four hours, twice a day because we come back to milk and feed them at 4 p.m. too. And that’s seven days a week including weekends, holidays, everything.”
Graduate students, specialists, postdocs, and a team of undergraduates all pitch in to keep the study running. Despite the long hours, McCabe calls the work meaningful and the teamwork energizing.
“You do it because you care about it,” he said.
One of McCabe’s standout memories at the CLEAR Center came far from California—at the UN Food and Agriculture Organization in Rome. There, he and CLEAR Center Director Dr. Frank Mitloehner joined international delegates to discuss livestock sustainability and methane mitigation.
“It was eye-opening,” he said. “Solutions that work in the U.S. won’t work everywhere. Most livestock are raised in other parts of the world. But seeing how much momentum there is globally. That was inspiring.”
As he nears the end of his PhD, McCabe is exploring roles in the food industry, hoping to help companies translate his technical expertise and research into on-farm practice and real-world application.
And the work he and the team have undertaken leaves a legacy far bigger than the dairy barn. It’s research that could shape how future generations farm, how companies meet climate goals, and of course, how livestock fit into all of it.