As California farmers work to curb methane emissions from the state’s sprawling dairy farms, they’ve found a convenient solution that helps control costs—and happens to offer benefits for the climate.

By feeding leftover nut shells from nearby almond orchards, dairy farmers not only support their neighboring farmers, they divert waste that would otherwise go into landfills where it generates methane. These leftovers also provide nutrition for the animals, replacing traditional forage like alfalfa that requires big swathes of farmland and copious amounts of water to grow.   

“From a sustainability standpoint, it’s a game changer,” said Michael Boccadoro, a longtime livestock industry consultant and president of West Coast Advisors, a consulting firm and advisor to the dairy industry. “It means less land, less water, less energy, less fertilizer, less pesticides and less greenhouse gases.” 

A 2020 study by University of California at Davis researchers demonstrates the benefits of feeding cows the material left over after an agricultural raw material is processed. Dairy farmers in California feed their cows other by-products, too, including spent grains from breweries, and vegetable scraps. Much of this would end up in landfills if not fed to cows, because it’s either too expensive to transport to other markets or has little value beyond cow feed, the researchers say.

Shrinking the Carbon Footprint

The report found that if dairy farmers were unable to feed their cows these by-products, they’d need traditional forage, like alfalfa, instead. Producing that would require “1 million acres and 4 million acre-feet of water,” and would raise feed costs by 20 percent, the researchers found.

Cows’ unique digestive systems enable them to turn these by-products into usable food that would otherwise go to waste. But their digestive systems also emit large amounts of methane, an especially potent greenhouse gas.  More than half of California’s methane emissions come from cattle operations, mostly from dairy cows. 

As California, the nation’s biggest dairy-producing state, tries to reduce its overall greenhouse gas emissions—40 percent by 2030 and 80 percent by 2050— the dairy industry has come under pressure to shrink its carbon footprint. The state’s powerful dairy industry blocked methane regulations for a decade, but in 2016 the state passed a law requiring the livestock industry to cut methane emissions 40 percent by 2030.

To meet the goals, California dairy farms have been taking on a variety of initiatives to reduce greenhouse gas emissions, including building dairy digesters that capture methane, burning it to make electricity or turning it into renewable gas. The state’s Department of Food and Agriculture is also promoting manure management programs to reduce greenhouse gas emissions from cattle droppings, another significant source of methane from the production of dairy products.  The industry claims it generates 45 percent less greenhouse gas emissions today than it did 50 years ago to produce a glass of milk from a California dairy cow. 

But feeding the animals is also a significant source of greenhouse gases, and the researchers point out that incorporating by-products into cows’ diets is a key component in the dairy industry’s efforts to cut climate-warming emissions. If dairy farmers can find the optimal diet for their cows—one that makes them more productive, but also uses fewer resources—that, in theory, shrinks the industry’s carbon footprint overall. Most dairies in California have nutritionists that design specific diets to make cows more productive. The industry says these efforts are working.

“The number of cows in California is starting to decline,” Boccadoro said. “Production is staying the same, but we’re able to achieve the same level of production, every year now, with fewer cows. This means that our carbon footprint is being reduced naturally through better efficiency and improved use of by-products.”