A stomach with four rooms
Why Does a Cow Chew All Day?
Grass is almost impossible to digest. A cow's answer is to eat it, ferment it, bring it back up and chew it again.
-
Step 1 of 5
Grass is locked up.
The energy in grass is wrapped in cellulose, and no animal on Earth makes a chemical that can cut it. Eat grass with a stomach like yours and most of it comes straight out again.
-
Step 2 of 5
Microbes can cut it, so the cow keeps some.
The first stomach is a warm tank holding billions of bacteria that do have the right chemical. The cow feeds them grass; they break it down and the cow lives off what they produce.
-
Step 3 of 5
Chewing twice is the trick.
Microbes work on surfaces, so the more the grass is torn up the faster they get through it. The cow swallows fast, then brings up a lump later and grinds it properly while resting.
-
Step 4 of 5
Four rooms, each with a job.
The tank ferments, the second sorts what still needs work, the third squeezes water out, and only the fourth is a stomach like yours — acid, digesting the microbes themselves.
-
Step 5 of 5
Side to side, not up and down.
Watch a cow's jaw and it swings sideways, grinding flat teeth across each other like millstones. Your jaw mostly goes up and down, which crushes but does not grind.
A cow has no top front teeth. It presses grass against a hard pad and tears it off by pulling with its head.
The short version
A cow lives on grass by fermenting it with microbes in a huge first stomach and chewing the same mouthful twice.
Try it yourself
Chew a piece of bread for a full minute without swallowing. It slowly turns sweet — that is your own chemistry cutting a chain open.