Tum! Tum! Tum! Tum! or How Many Stomachs Does a Cow Have?

Quick, without looking it up, how many stomachs does a cow have?

Did you guess "four?"

Well, you're almost right.

Don't worry, I grew up hearing that cows have four stomachs, too!  You could say cows have one stomach with four parts.  But to be strictly accurate, they really have three pre-stomachs which are actually part of their esophagus along with one real stomach.

Here, then, is everything you've always wanted to know about a cow's stomach--and then some!

Get ready to be shocked, moms:  Cows don't properly chew their food before they swallow it.  And get ready to be grossed out, kids:  Cows belch their food back up from their stomach into their mouths, then chew it and swallow it again!  Sorry if that was T.M.I., but if you're a sucker for yuck, here's how it works . . .

Because a cow doesn't have upper teeth in front, she sweeps up grass or hay with her rough tongue, pinches it between her lower teeth and a "dental pad" (where your top teeth are), and rips it off.  She chews it briefly to mix it with saliva in her mouth (especially important for dry hay), and then swallows it.  By the way, a cow can produce over 20 gallons of saliva a day.  She recycles much of the water in that saliva--and that's probably all you want to know about that!

Image from Animal Corner.co.uk--http://www.animalcorner.co.uk/farm/cows/cow_anatomy.html

The four digestive compartments in the cow are called:

1. The Rumen is where the term "ruminants" comes from.  The rumen is the largest compartment, containing up to 50 gallons of food in a full-size cow.  (Of course, a Dexter's rumen is proportionally smaller.)  The rumen is full of good bacteria, molds, yeast, etc.  When I say "full," I mean numbering in the billions!  These microorganisms live in harmony with the cow and break down the food to enable her to digest it.  The rumen with all its micro-organisms is particularly designed to digest grass and hay which would be mostly indigestible to humans.  After bacteria in the rumen begin to break down the food, the cow regurgitates a "bolus" of partially chewed food into her mouth to chew it again.  This is called "rumination" or "chewing her cud."  When the cow swallows the chewed cud it goes directly into other chambers of her stomach.  (Who knew a cow has a "smart stomach" that knows where to send the food?!)  The cow also "eructates" or belches, emitting carbon dioxide and methane. 
2. The Reticulum, with its lining that resembles a honeycomb, works along with the rumen to circulate the undigested food and keep the rumen from getting clogged.  When a cow swallows her partially-chewed mouthful, the liquid part goes into the reticulum while the solid part goes into the rumen.  Remember that cows pull grass and hay into their mouths with their tongues and don't chew it well?  Unfortunately, sometimes along with her food, a cow swallows other stuff that is lying around.  Things like pieces of barbed wire, rocks and nails can end up in a cow's reticulum.  This causes "hardware disease," a very serious condition that is difficult to treat, but fairly easy to prevent.  Stay tuned for a future post!  
3. The Omasum is where the chewed cud ends up.  It serves as a pump to move the food on into the real stomach, the abomasum.  The omasum is sometimes called "the book" because it has many leaves like the pages of a book.  It reabsorbs water, sends small food particles on to the abomasum and sends larger pieces of food back to the reticulum and rumen for a "do-over."
4. The Abomasum is called the "true stomach."  It functions like a human stomach using acid and enzymes to begin protein digestion.

Up close and personal!  Sara "ruminates" or chews her cud.

A cow's "four tums" (or as you now know, three pre-tums and a real tum) allow her to efficiently turn grass and hay into life-sustaining energy for herself and milk for her calf . . . and some for her humans, too.  The cow chews her cud about eight hours a day, a sign that she is healthy and happy.

So move over California, happy cows come from anywhere as long as they're chewing their cud!

The information in this post came largely from the following online resources:
Virginia Cooperative Extension, Digestive System of the Cow by John B. Hall and Susan Silver
The Dairy Mom blog, Content Cows Chew Cud, by Brenda Hastings