Why do cows chew their cud?

In my home country of Jamaica, cattle was prevalent. I would watch them from time to time and they would stand there lazily and chew - for what seems to be - forever. I have always wondered: "Why is that?" However, I never got a good answer. It seemed like no one could explain to me why an animal would chew its cud.

Many years later, I was in comparative anatomy class and the professor was discussing different types of digestive systems and fore gut fermenters was mentioned. Up until then, I was quit naive about the gastrointestinal (GI) tract of other animals that are not human. I mistakenly assumed that all GI tracts looked like the one of the human. although I was somewhat right, many animals in different niches have special modifications to their GI tracts so that they could properly digest and absorb their food of choice. The cattle is one such example. The bird and the horse also has specialized GI tracts and I may talk about that in detail in a later blog post.

Okay, let's get started. The cow's stomach is consisted of four parts: the rumen, reticulum, omasum and abomasum. Food (which mostly plant based) enters the mouth and travels through the esophagus to the rumen. The plant based food that a cattle consumes consists of a type of sugar called cellulose. Mammals lack the ability of  breaking down cellulose on their own, therefore, when the plant based food enters the rumen of a cattle, it is met by a team of microorganisms that aid in the digestion of cellulose.

These microorganisms are classified as protozoa and bacteria. They form a symbiotic relationship with the cattle. The microorganisms are capable of synthesizing cellulase, an enzyme that breaks down cellulose. When cellulose is fermented by the microorganisms, it is broken down into short organic acids, methane, and carbon dioxide. The saliva of the cattle is used as a buffer in which the microorganisms proliferate. The saliva also aids in detoxifying toxins such as alkaloids which may be in the food.

In order for cattle to get protein in their diet, the microorganisms in the rumen converts the simple nitrogenous compounds in the food into ammonia then the ammonia is used to make protein. Another way that the cattle gets its protein is through inhaled nitrogen in which the microorganisms convert to protein.

From time to time, the cattle would belch. In doing so, it releases some gas produced in the reticulorumen and also regurgitate some of its food. The food that is regurgitated is re-chewed or re-masticated by the cattle. This re-mastication is what we see when a cattle is chewing its cud! This cycle is repeated on numerous occasions until the physical substance is broken down enough to get past the reticulum, into the omasum and abomasum. The absomasum is where protein digestion normal protein digestion starts.

Hopefully, I didn't get too technical there. I was really trying not to. However, that is the process that happens inside the anterior region of a cattle's GI tract. The cattle has evolved a mechanism that effectively extracts most of the nutrients of the plant matter that it could. What about horses and rabbits? They don't chew their cuds and they consume plant matter ... Yes, they do not chew their cud, however in their GI tract, they have a cecum in the hind region. The cecum contains a team of bacteria that breaks down the cellulose. Rabbits have been observed eating their own feces in order to extract more nutrients from their food. These mammals are called hingut fermenters.

Hope that helped! Be sure to comment, share and subscribe to my Youtube channel Knosis, where I post science and technology videos!

Reference: Liem, Karl, et al., Functional Anatomy of the Vertebrates: An evolutionary perspective. 3rd ed. Belmont, CA: Emily Barosse . Print

The Purpose

Update (3/10/2019): It has been a number of years since I have updated this blog. I have had it on my to-do list for a while now, however, I have not prioritized it. I am starting medical school in 3 months and I plan on utilizing this space to write about the information that I find most interesting. It will be a great way for me to review my notes and to help out anyone who comes across this blog. I intend on dedicating at least 30 minutes a week to write about a topic that I find interesting from the previous week. Be sure to follow the blog to see what is to come!


As a young boy growing up, I had many questions for my older siblings and parents of why the world operates the way it does. Questions like "Why do cows chew their cud?" was one of the questions that I never got a complete answer for. Until I took comparative anatomy of chordates, in my third year of studying Biology. Okay, maybe if I really wanted the answer, I could of just Googled it eventually when I gained access to a computer, but the question faded away from my mind.

This blog is created to answer many of the common questions people ask as children but never got a complete answer for. Questions that will be covered will include, but not limited to: Why do we have fingernails?, Why are women and men so different? and are they really that different?, Why is the sky blue? How solar panels work? Why are some words bad and others that mean the same exact thing not bad?

These and other questions will be answered in future blog post. Enjoy your day Homo sapiens.