How Many Stomachs Does a Cow Have?


Feeding entirely on grass and other similar plant products for their diet, cows have got huge stomachs that take up a significant share of their physiology. This guide will answer how many compartments the cow has in their stomach and what each does.

A cow has one stomach that contains four separate compartments and is the reason why cows are classified as ruminants. The four compartments of a cows stomach are the rumen, reticulum, omasum and abomasum. Each part of the stomach breaks down their food to allow them to extract every nutrient.

If you want to know why cows need multi-part stomachs, as well as what each of them does when it comes to digesting the food, read on to get some great information.

Why Do Cows Have Four Stomachs?

Humans are versatile eaters that can eat plants as well as other plant-eating animals, while also deriving the required amounts of sugar out of the cell walls of the consumed food. 

However, we can’t derive energy from raw grass and other dense vegetation as our digestive systems aren’t equipped to break such food down. 

On the other hand, cows are classified as ruminates and ungulates, which means that they have to feed on plants that are hard to digest, including grass. This is why their digestive systems must be reliable and efficient enough to break such food down. 

Cows do this by regurgitating and re-chewing their food, further breaking it down and extracting more of the nutrients from it that are finally absorbed into their bodies.

The fact that they depend on the nutrients in the grass is the reason why cows have four stomachs when most animals do just fine with one. 

Although grass is the primary diet of a cow, many other leaves and plants also make up a large part of their diet. The problem with grass is that it is not easily digestible nor very nutritious when consumed in small amounts. 

Cows have to consume vast amounts of grass to get the right amount of nutrients. This is the reason that they spend so much more time grazing grass than carnivores do when hunting and eating their meals.

Although a large number of mammals eat fruits or soft young leaves, there is not enough fruit readily available for big grazing animals like a cow as they are not a forest-dwelling species. 

However, they have come up with an efficient way of extracting maximum nutrition even from mediocre quality food. This is why over time cows have evolved in a way that has allowed them to take their nutrition from their surroundings.

How Does A Cows Stomach Help Them Eat Grass?

Apart from having ruminant stomachs, cows also have a unique mouth construction and an equally unique set of teeth. Cows are herbivores making it essential for them to consume large amounts of fiber, which they derive from grazing. 

Containing a total of 32 teeth, their mouths feature two canines and six incisors. The canines on the bottom front are combined with a dental pad atop the cow’s mouth. 

Their mouths enable them to consume large amounts of grass at once. The canines in their mouths perform quite similar to incisors when it comes to cutting through the grass. A large gap separates the front teeth.  This gap along with the dental pad present in the cow’s mouth enables the cows to grind the grass from side to side.

Before all that grass reaches the stomach, it needs to be thoroughly chewed. Cows are known to munch for surprisingly long durations, approximately eight hours a day. During grazing, cows snatch up large bites of grass to consume as much as possible in rapid time. This proves to be quite useful for cows in the wild by limiting the time that they expose themselves to predators. 

Usually, the plant matter or grass is combined with tough stems, but the cows chew their food in a motion that works from side-to-side.  This allows their molars to break down the grass into smaller bits that are much easier to digest.

Usually, cows graze and get full at the same time.  They follow this by laying around. It’s only later on that they begin chewing the grass that they swallowed. When the grass enters the cow’s stomach, each compartment plays their very own role in the digestion of the grass. 

Cows swallow the grass whole until the rumen is filled. After the rumen, the grass then travels to the reticulum. Once the food reaches these first two chambers of the stomach, the partially chewed grass sits in these compartments that work as storage vats. 

When some portion of the grass is partially digested, this then travels to the reticulum.  In the reticulum this is where the cows regurgitate the grass matter from the rumen and start chewing it all over again. This action is also known as chewing the cud. 

Once the first two compartments work their part, and the chewing action breaks down the food into tiny pieces, the food is passed to the omasum and abomasum for further digestion.

The Stomachs

Each of the four compartments of a cow’s stomach plays their very own role and have some unique characteristics that are listed below.

Rumen

The very first and the largest compartment of the cow’s stomach is known as the rumen. At any given time, the rumen can hold up to a surprising 50 gallons of half-digested food. It contains lots of enzymes that break down the hard food bits and cellulose.  The rumen also acts like a huge tank filled with a vast bacterial population and food. It is a vast fermentation vat that has about 200 different bacteria and 20 varieties of protozoa.  

Reticulum

The next part of the stomach is known as the reticulum. Also known as the ‘hardware’ stomach, the reticulum also contains bacteria.  This also allows the cow to regurgitate the food and chew it all over again. 

The rumen and reticulum serve separate functions. The reticulum does not contain any acid which prevents the food from having a bad taste when the cow regurgitates its food. 

If the cow consumes something inedible along with the food, such as metal or wood from fences, the reticulum ejects it out.  The reticulum also softens the consumed grass and forms small pieces of cud.

Omasum

The third compartment of the stomach, the omasum, is characterized by folds that increase the surface area of absorption, specifically about 4-5 meter square. 

The presence of numerous folds makes the omasum quite hard, while the surface of the compartment absorbs 30-60% of the total water intake and vital nutrients, including sodium and potassium. The folds also prevent the flow of large particles through the cow’s digestive system. 

Abomasum

Also known as the ‘true’ stomach in ruminants, the abomasum is the fourth compartment of the cow’s stomach.  The abomasum works similar to a human stomach. 

It is connected to the intestines and helps in digesting the protein from the food as well as ruminal microbes by producing gastric juices. 

How Do Cows Digest?

The ability to digest food and break it down to absorb vital nutrients isn’t the same for all animals. Cows have a digestive system that hugely differs from ours, which allows them to survive mainly on grass. 

As mentioned above, cows eat their food, regurgitate it, and consume it once again. When the cow consumes the food, it enters the rumen where it’s layered atop the rumen mat. 

Regular contractions of the walls of the rumen lead to the accumulation of the freshly eaten food to the rear section of the mat. The mat consists of non-digested food with about 15% of dry matter. 

Bacteria present in the rumen combine to the food, gradually digesting the fermentable material. Saliva is secreted inside the mouth of the cow, while the grinding action of their teeth exposes larger surfaces of food to the bacteria. 

The rumen creates favorable conditions for bacteria to break down the cellulose through fermentation, which is quite similar to the action of yeast. The bacteria then break down the cellulose present in the food. 

As the process continues and as the bacteria works, the food particles become smaller and smaller. As the particles absorb fluid, they sink to the rumen’s bottom. 

The contractions in the rumen take place once every minute, thereby allowing the mixing of solid contents and liquid to allow fermentation. 

Although not entirely digested, some of the grass or plant matter is broken down. Smaller cuds of food are broken down during the process of rumination.  Overall, the food spends 15-48 hours in and out of the rumen. 

Throughout the process, the food undergoes chewing, swallowing, regurgitating, followed by the cow swallowing it again. The action of the bacteria on the food produces fat, which is the source of most of the energy for the cow. 

Next, the food advances to the reticulum. Although most of the fermentation takes place in the rumen, the reticulum works to provide a passage for the food into regurgitation or the omasum. 

The reticulum separates the food that is ready from the food that needs more chewing and is further broken down.  The reticulum also traps inedible items such as tiny pieces of wire, rocks or pieces of fencing which the cow ejects orally.

When the cow chews the food once again, it is transferred to the sponge-like omasum. This is the compartment where water and some previously broken down nutrients begin to be absorbed. 

The omasum sucks out minerals, water, and salt, further returning them to the rumen to ensure the maintenance of an optimal environment for the bacteria to thrive. Bits of food that require further digestion are passed on to the abomasum.

The abomasum secretes bile and acid to break down the food further. Some bacteria cells that carry out the break down of the cellulose in the rumen also travel to the abomasum, where they undergo further break down and are digested.

The abomasum is another spot where the absorption of nutrients takes place. Also known as the ‘true’ stomach, the abomasum mixes the food with acid, the cow further churns it by squeezing and relaxing its muscular lining. 

When the food is adequately mashed and pureed, it releases the remaining amounts of sugar. Lastly, the little remaining food leaves the stomach and is passed on to the intestines.

How Do The Intestines Help Digestion?

Once the actions of the four compartments of the stomach are completed, the food reaches the intestines where it’s further broken down to absorb nutrients. 

Small Intestine

An elongated tube that connects the abomasum with the large intestine, the small intestine is about 20 times the length of a cow.  A cow that is two meters in length has got a small intestine approximately 40 meters long. 

This is the part where a significant proportion of the process of digestion takes place, including the absorption of water and vital nutrients. 

When the food passes through the abomasum, it reaches the small intestine, where it’s mixed with the pancreatic secretions. 

The nutrients are enzymatically broken down to allow for efficient absorption of all the sugars, amino acids, and fatty acids, along with water via the tiny villi present throughout the walls of the small intestine.

The Large Intestine

A significant spot for mineral absorption, the large intestine also plays a crucial role in absorbing, re-circulating, and conserving water for the cow. 

The caecum and colon present in the large intestine lead to an active fermentation that may provide for about 10-15% of the total energy transported to a dairy cow. A significant amount of the microbial protein yielded by fermentation is lost in the form of manure.

Once the digestion process is complete, abundant amounts of energy in the form of fat, sugar, and protein is free for use by the cow. The molecular bonds of these nutrients house all the energy that’s released as and when it’s needed by the animal while storing a small share of that energy to be used later.

Why Is The Cows Stomach Important To Dairy Farmers?

The rumen of a cow is very efficient in extracting nutrients from the food that is hard to digest for most animals. This is why cows can easily have stems, shells, seed coats and other plant materials that are left after the grains are harvested. 

Also known as by-products, these plant materials don’t need to be disposed of.  Instead, they can be sold as cow feed.  This also helps farmers and other businesses save a great deal of money as they don’t have to pay for the disposal of by-products anymore.

Plant by-products are also made when grains are used to produce fuel-ethanol, brew alcohol, or extracting oil. During the process, the vital nutrients, including proteins, sugar, and fat, are removed from the grains, but what remains is the by-products that can be conveniently fed to cows. 

The efficient action of the four stomachs and the bacteria in the rumen make these by-products edible for cows. This is the reason that farmers and dairy staff can manage their herds for a beneficial production of the milk and meat that is for human consumption. 

Bryan Harding

Bryan has spent his whole life around animals. While loving all animals, Bryan is especially fond of mammals and has studied and worked with them around the world. Not only does Bryan share his knowledge and experience with our readers, but he also serves as owner, editor, and publisher of North American Mammals.

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