It’s an oppressively hot morning in the barnyard, even in the shade of the long open-air structure where the cows come to feed. On a typical farm, they would gather around a trough, but here at UC Davis they chow from special blue bins, which detect when and how much each one eats. It’s like Weight Watchers, only researchers here aren’t so much interested in these cows’ figures, but how much they burp.
Animal scientist Frank Mitloehner leads me to another kind of feeder, one that could easily be mistaken for a miniature wood chipper. He grabs a handful of the alfalfa pellets that the machine dispenses when it detects that a cow has poked its head in. “This is like candy to them,” Mitloehner says. I stick my head into the machine as Mitloehner points out a small metal tube within: “This probe measures the methane they exhale, and that happens every three hours for all the animals in this study.”
Cows, you see, have a serious emissions problem. To digest tough plant material, their cavernous stomachs act as fermentation vats. They’re teeming with methanogens, microbes that process cellulose to make volatile fatty acids, which the cows turn into meat and milk. But those methanogens also produce methane, a particularly nasty greenhouse gas that is 80 times more potent than carbon dioxide, thanks to the way its molecules vibrate to absorb infrared radiation. These gases capture heat, and that means more global warming.
“The methane is a byproduct—an unintended consequence, I'd say—of the unique ability of ruminant animals to digest cellulose,” says Mitloehner. But just because cows can eat it doesn’t mean it’s easy for them. Because the plants cows eat are nutritionally poor, the animals have to eat a lot of food to survive, and periodically bring it back up from their four stomachs to ruminate it again—that’s “chewing the cud.” That leads to incessant burping or, as scientists call it, enteric emissions.
Now multiply those burps by the world’s huge cattle population. To satisfy humanity’s bottomless appetite for beef and milk, a billion head of cattle now roam the planet. A paper published in September in the journal Nature Food by an international team of researchers found that the global food system generates a staggering 35 percent of total greenhouse gas emissions. Beef is responsible for a quarter of those food emissions, with another 8 percent coming from milk production.
However, methane lasts only for about a decade in the atmosphere, while carbon dioxide persists for centuries. If scientists can figure out how to get cows to stop belching so much, that would make a big dent in emissions, and we’d see the climate effects almost immediately. So Mitloehner and other researchers are experimenting with food additives like seaweed, garlic, and even essential oils derived from plants like coriander seed, which tweak the animals’ gut environment in different ways, for instance by disrupting the enzymes that produce methane. They’re also playing around with biochar—charcoal, basically—which soaks up methane in the gut.
That’s why Mitloehner is going to such lengths to quantify his cows’ diets: Using the high-tech troughs and snack-dispensing methane detectors, he can show how well a particular technique might reduce enteric emissions. “We have found that, depending on what additive you are dealing with, we can reduce enteric emissions anywhere between 10 to 50 percent, and that is sensational,” says Mitloehner.
Earlier this year, a team co-led by his UC Davis colleague, animal scientist Ermias Kebreab, published research showing a gas reduction of up to 82 percent with seaweed additives. But studies from scientists testing other additives have shown lower degrees of effectiveness. A 2019 study from Wageningen University and Research that looked at the organic compound 3-nitrooxypropano, or 3-NOP, found up to a 50 percent reduction. One by researchers in the UK and Switzerland found that Agolin, a mixture of essential oils, reduced methane production by only 6 percent. In New Zealand, cows fed tannins showed a 13 percent reduction.
And the concept of rolling out a feed additive to the world’s billion cows faces some logistical challenges. “The truth is that the benefits of seaweed are likely far more limited, both in its capacity to reduce cows’ methane emissions and its potential to scale up to the size of the problem,” wrote researchers Matthew Hayek and Jan Dutkiewicz in WIRED earlier this year. They noted that cows produce the most methane when they’re grazing in a pasture, eating all that grass—the hard-to-digest stuff. That’s where most cattle spend most of their lives; they live on feedlots, where it would be easy to add additives to their diets, only in their final months when they are being fattened for slaughter. The researchers estimated that cows belch just 11 percent of their lifetime methane during those months on feedlots.
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That’s an issue, Mitloehner acknowledges. “The challenge will be to get these into free-range cattle that are not fed at a trough,” he says. “One way might be via salt licks, or maybe via drinking water. Work is also ongoing to put these active ingredients into a slow-release bolus to be placed in the cow’s stomach system.”
He also wants to avoid side effects. “The higher you go with your [emissions] reduction, the more likely you are to run into unintended consequences,” he says. For instance, the researchers have to track the animals’ weight to make sure the additive isn’t affecting growth. They also have to consider palatability—maybe cows don’t like their food tasting like garlic. Or the animal might end up burping less, but their milk could come out tasting weird. “We have to find out what the happy medium is,” he says.
Farmers in economically-developing nations might be particularly hesitant to feed their animals anything that could cause side effects. “As long as there is a financial incentive to feeding these additives, they will likely be accepted by farmers and ranchers” in developed nations, says Mitloehner. “It will be much more challenging to reduce methane in places like Africa or Asia.”
In the meantime, Kebreab is working with agriculture officials in countries like Vietnam and Ethiopia to tackle something those farmers may find more urgent: productivity. Boosting how much milk and meat cattle produce can reduce their carbon footprint, because farmers can realize similar gains with fewer animals.
This has already happened in the United States: The numbers of cattle have shrunk, yet the country is producing more beef and dairy. US beef consumption has stayed fairly flat, while dairy consumption has steadily declined with the rise of alternatives like soy and almond milk. But herds have been downsized because cows are more productive thanks to advances in breeding, veterinary care, and nutrition.
“One animal is now producing what two, three, or four animals were producing 50 years ago,” says Kebreab. “And because of that, a kilogram of milk is actually about 45 percent lower in its carbon footprint.” Because an individual cow produces much more milk, you don’t need as many cattle. And because those gains also coincided with gains in crop yields, an acre of land now produces more food for cows. (That acreage isn’t negligible: 41 percent of the land in the contiguous US is used for feeding livestock—654 million acres for pasture and 127 million acres to produce feed.)
In low-income countries, by contrast, productivity remains low, Kebreab says: “One cow is making four or five liters [of milk] a day, and here, in our herd, 40 liters is an average.” To boost productivity in developing nations, Kebreab is working on software that’ll determine what kind of feed formulation is best for a particular breed of cattle.
Making cattle more productive would help with another emissions problem: The fewer cows you have, the less land you have to clear for them to graze. In Brazil, for instance, ranchers are burning swaths of the Amazon rainforest to make room for cows. An investigation by the NGO Global Witness last year found that in just one Amazon state, over the course of three years, beef companies bought cattle from ranches responsible for 20,000 football fields’ worth of illegal deforestation. “That disturbance is going to release carbon to the atmosphere,” says University of Illinois climate scientist Atul Jain, a coauthor on the Nature Food paper. Plus, growing grain for your cows requires tilling the land. “That also would release carbon from the soil, because soil is one of the major reservoirs for carbon dioxide,” Jain says.
You might be thinking that it would be easier to solve the problem if we all just consumed less meat and milk. The answer is that some people can—but some can’t. Americans have plenty of alternative proteins, like the Impossible Burger. (A recent analysis by the Good Food Institute, which promotes the alternative protein industry, calculates that compared to regular meat, producing plant-based meat uses between 47 and 99 percent less land and between 72 and 99 percent less water, and emits between 30 and 90 percent less greenhouse gas.) But to many people around the world, a cow is much more than food. A cow can be an asset—not only as a critical source of protein and nutrients like iron, but as a working animal and a kind of currency.
As more people ascend into the middle class, the demand for meat will increase globally, and Jillian Fry, a public health scientist at Towson University, says that people in industrialized nations should forgo meat more often to help strike a balance. “That makes it even more urgent for us to shift our diets toward plants—not 100 percent, but toward plants—so that we're freeing up resources so that folks who don't have the food to meet their basic needs and health will have access to that,” she says. “We've known for a long time that our Earth does not have the resources to support the world eating the way that Americans do.”
Mitloehner doesn’t think this is the most efficient way to go. The market share of alternative proteins remains small, he says, even after years of hype. “All of that considered, neither the production nor the consumption of animal-sourced foods in the US play anywhere close to the role that the fossil fuel sectors—transport, power, and cement—play, which make up 80 percent of our nation’s carbon footprint,” says Mitloehner. “We will do what we can with livestock, but let’s be real about the elephant in the room.” That’d be fossil fuels.
For her part, Fry thinks there’s a danger of using methane-cutting feed additives to prop up a business-as-usual food system. Additives might reduce emissions, but they won’t fix the fact that ranchers are mowing down forests to make way for cows. “The expanding desire for meat, and especially production of cattle, is a major driver of this deforestation,” says Fry. “And there's no way to reverse that impact on the climate by adding seaweed to feed.”
She worries that the meat and dairy industries might choose additives over making other changes. “If the industry can hold up one strategy about reducing methane emissions, that's their shiny object to distract people from multiple larger issues that need to be addressed,” she continues.
A lot of hot air, if you will.