Cows 101: A Quick Bovine Anatomy Lesson

Posted by TF Oren

Cows: They chew their cud, have a few stomachs (how many was that, again?), look adorable with bells on, and make for lovable cartoon characters (often named Daisy). 

But how much do we really know about their physiology? Here’s a basic bovine anatomy lesson on our polygastric friend, the cow.

Cows, like goats, sheep, deer, yaks, and even giraffes, are ruminants, which means that they have a four-compartment stomach. The four compartments are: the rumen, the reticulum, the omasum, and the abomasum.

As a cow chews, digestive enzymes in its saliva mix with the food. The digesta (the term for food in the digestion process) travels through the esophagus into the first two compartments, the rumen and the reticulum. Because digesta flows freely between both compartments, they are collectively referred to as the reticulorumen.

The reticulorumen is where digesta separates into solid and liquid material with the help of a few different types of specialized microbes. The solid material is called bolus, or, in more familiar terms, cud.

Though most digesta is processed and fermented in the reticulorumen, a portion of it gets regurgitated, re-chewed, and then swallowed a second time.

This is the technical, animal science explanation for the term “chewing the cud.”

Ruminant stomach.

Once the digesta has been processed, it descends to the lower part of the reticulorumen and on into the next compartment, the omasum. Whereas the reticulorumen is responsible for upwards of 50% of the digestive tract’s functional capacity, the omasum is responsible for only 6-8%, according to cattle expert Robert Fears.

The omasum is a structure composed of folded tissue where water and other inorganic elements in the digesta get absorbed into the bloodstream.

When the digesta leaves the omasum, it travels into the abomasum, which is often referred to as the true stomach, and is the functional equivalent of a monogastric organism’s stomach. It’s where digestive enzymes (stomach juices) break the digesta into protein, carbohydrates, fats, and other nutrients in order for them to be absorbed into the small intestine.

Anything that cannot be digested travels to the large intestines, where the body reabsorbs excess moisture and forms fecal material. Depending on what the cow eats, digesta can remain in the digestive tract for up to three days.

And there you have it. So, the next time you’re in desperate need of some unusual cocktail party conversation, or hear someone haphazardly quoting an incorrect number of stomachs, you can swoop in with a little geek bravado and wow your audience with a quick lesson on ruminant anatomy.

Do it for the cows.

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Cows 101: A Quick Bovine Anatomy Lesson