Why do cows burp methane? -Silas, 10, Seattle, WA

Dear Silas,

There are more than a billion cows on our planet and they all need to burp. Just like us, they burp to get rid of extra gas in their stomachs.

We can’t see this gas. But we can often hear the gas as it escapes the stomach and vibrates part of our throat. And sometimes we can smell it.

We usually burp out extra air we’ve swallowed and the gas from our fizzy drinks. But for cows, it’s a little different. As you’ve pointed out, they belch a gas called methane.

I met up with my friend Joe Harrison to find out more about cow burps. He’s an animal scientist at Washington State University.

Harrison explained that a big part of the reason cows burp methane is because of their special stomachs. Humans have just one stomach compartment, he explained, but cows have four.

The first compartment in the stomach is the rumen. Cows love to eat grass and other plants. They use it to make energy. But they can’t do it alone.

Something else is moving around in their rumen: microbes. You’d need a microscope to see these tiny creatures, but they do a lot of work in the cow’s stomach. Microbes and cows are like best buddies when it comes to digesting food.

In fact, cows can’t digest some parts of plants on their own. They need help from the microbes that live in their stomach.

Inside the rumen, microbes help break down small parts of the plant into even smaller parts the cow can use for energy. As they do this, the microbes also make different gases.

Sometimes the microbes make hydrogen. Sometimes they make carbon dioxide. Some microbes make methane.

As the gas builds up, the cows have to get rid of it. Out comes a stinky burp.

Methane is not just the stuff of cow burps. It is also a greenhouse gas. Scientists are asking big questions about how this gas traps heat in the atmosphere, warming the planet and creating challenges for our environment.

Buffaloes, goats, and other ruminants burp methane, too. They all have special stomachs with four compartments. While stomachs may be different, burping is one way animals, including humans, take care of themselves. It keeps gas from building up in our bodies.

One really easy way to make up some gas of your own is to use a balloon, baking soda, and vinegar. Pour a little vinegar into a plastic bottle. Put a little baking soda inside a balloon. Stretch the balloon over the top of the bottle, then tap in the baking soda.

What do you think will happen? What kind of gas is in the balloon? Try it out sometime and let me know what you think at Dr.Universe@wsu.edu.

Dr. Universe