Put That Cow on a Diet

A very short book excerpt

Joe McKendry

The planet’s 1.5 billion farm ruminants (cud-chewers such as cattle and sheep) emit methane equivalent to 7.1 billion tons of carbon dioxide a year in its heat-trapping effects. That’s nearly 15 percent of man-made CO2 emissions—as much as we put into the atmosphere from burning fuel for transportation.

About 10 years ago, two Australian scientists, Robert Kinley and Rocky de Nys, discovered that certain seaweeds added to cows’ feed lowered their methane emissions, but the high dosages required upset the bovines’ digestion. Then they tried Asparagopsis taxiformis, a macroalgae that looks something like a pink underwater fern and grows wild around Australia. In the lab, adding just a little of this seaweed—2 percent of feed—to artificial cow stomachs reduced methane output so much that it became virtually undetectable. Kinley, de Nys, and their colleagues have since demonstrated that sheep fed a little A. taxiformis produce up to 85 percent less methane. Preliminary reports from California are similarly encouraging: Cows eating a diet that is just 1 percent seaweed produce 50 percent less methane, and the reduction is immediate. What about the taste of their milk? In a blind test, 25 testers perceived no difference between samples from cows fed with and without seaweed. Good thing, because marketing milk with “a scent of the sea” would be a challenge.

—Adapted from Slime: How Algae Created Us, Plague Us, and Just Might Save Us, by Ruth Kassinger, published by Houghton Mifflin Harcourt