Feeding entirely on grass and other similar plant products for their diet, cows have huge stomachs that take up a significant share of their physiology. This guide will answer how many stomachs a cow has and what the four compartments do.
A cow has one stomach containing four separate compartments. The four compartments of a cow’s stomach are the rumen, reticulum, omasum, and abomasum. Each part of the stomach breaks down its food to allow them to extract every nutrient.
If you want to know why cows need multi-part stomachs and what each of them does to digest the food, read on to get some great information.
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Do Cows Have Four Stomachs?
Cows do not have four stomachs. Cows have one stomach with four compartments, and cows have these as they eat differently from us.
Humans are versatile eaters that can eat plants and animals while getting the required amounts of sugar out of the consumed food’s cell walls.
However, we can’t get energy from raw grass and dense vegetation as our digestive systems aren’t equipped to break down such food.
Cows are classified as ruminates, which means that they have to feed on plants that are hard to digest, including grass. Their digestive systems must be reliable and efficient enough to break such food down.
Cows regurgitate and re-chew their food, further breaking it down and extracting more nutrients.
The fact that they depend on the grass’s nutrients is why cows have four compartments’ when most animals have one.
Although grass is the primary diet of a cow, many other leaves and plants also make up a 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 proper nutrients. They spend so much more time grazing than carnivores do when hunting.
Although many mammals eat fruits or soft young leaves, there is not enough fruit readily available for big grazing animals like cows as they are not a forest-dwelling species.
However, cows can efficiently extract maximum nutrition even from mediocre quality food. This is why, over time, cows have evolved in a way that has allowed them to eat hardier plants.
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How Do Cows Eat Grass?
Besides having ruminant compartments’, cows also have a unique mouth construction and an equally unique set of teeth. Cows are herbivores making it essential to consume large amounts of fiber, which they derive from grazing.
Containing 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 similar to incisors when cutting through the grass. A large gap separates the front teeth. This gap and the dental pad in the cow’s mouth enable the cows to grind the grass from side to side.
Before all that grass reaches the stomach, it must 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 helpful for cows in the wild by limiting the time 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 lying around. It’s only later that they begin chewing the grass they swallowed. When the grass enters the cow’s stomach, each compartment plays its 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 stomach chambers, 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, the cows regurgitate the grass from the rumen and start chewing it again. This action is also known as chewing the cud.
Once the first two compartments work and the chewing action breaks down the food into tiny pieces, the food is passed to the omasum and abomasum for further digestion.
Compartments Of A Cows Stomach
Each of the four compartments of a cow’s stomach plays its role and has some unique characteristics listed below.
Rumen
The first and the largest compartment of the cow’s stomach is known as the rumen. The rumen can hold up to a surprising 50 gallons of half-digested food at any given time. It contains many enzymes that break down the complex food bits and cellulose. The rumen also acts like a giant tank filled with a vast bacterial population and food. It is an enormous 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 contains bacteria. This also allows the cow to regurgitate the food and chew it again.
The rumen and reticulum serve separate functions. The reticulum does not contain any acid, which prevents the food from tasting foul when the cow regurgitates its food.
The reticulum ejects it out if the cow consumes something inedible along with the food, such as metal or wood from fences. 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 absorption surface area, specifically about 4-5 meters square.
Numerous folds make the omasum quite hard, while the compartment’s surface 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 similarly to a human gut.
It is connected to the intestines and helps digest the protein from the food and ruminal microbes by producing gastric juices.
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How Do Cows Digest Food?
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 differs hugely from ours, allowing them to survive mainly on grass.
As mentioned above, cows eat their food, regurgitate it, and consume it again. When the cow consumes the food, it enters the rumen, where it’s layered atop the rumen mat.
Regular contractions of the rumen walls lead to the accumulation of freshly eaten food in the rear section of the mat. The mat consists of non-digested food with about 15% of dry matter.
Bacteria in the rumen combine with the food, gradually digesting the fermentable material. Saliva is secreted inside the cow’s mouth, 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, similar to the action of yeast. The bacteria then break down the cellulose present in the food.
As the process continues and the bacteria works, the food particles become smaller and smaller. As the particles absorb fluid, they sink to the rumen’s bottom.
The rumen’s contractions occur once every minute, allowing the mixing of solid contents and liquid to allow fermentation.
Although not entirely digested, some 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.
The food undergoes chewing, swallowing, and regurgitating, followed by the cow eating it again throughout the process. The bacteria’s action on the food produces fat, the source of most of the cow’s energy.
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Next, the food advances to the reticulum. Although most fermentation occurs in the rumen, the reticulum works to provide a passage for the food into regurgitation or the omasum.
The reticulum separates the ready food from the food that needs more chewing and further breaks down. The reticulum also traps inedible items such as tiny pieces of wire, rocks, or fencing that the cow ejects orally.
When the cow chews the food, 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, returning them to the rumen to ensure 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 cellulose breakdown in the rumen also travel to the abomasum, where they undergo further breakdown 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 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 a small intestine approximately 40 meters long.
This is where a significant proportion of digestion takes place, including the absorption of water and vital nutrients.
When the food passes through the abomasum, it reaches the small intestine, mixed with the pancreatic secretions.
The nutrients are enzymatically broken down to efficiently absorb all the sugars, amino acids, and fatty acids, along with water via the tiny villi present throughout the small intestine walls.
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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 are present in the large intestine leading to an active fermentation that may provide 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 fat, sugar, and protein are free for use by the cow. The molecular bonds of these nutrients house all the energy released as and when 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?
A cow’s rumen 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 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 lot of money as they no longer have to pay for by-products’ disposal.
Plant by-products are also made when grains are used to produce fuel ethanol, brew alcohol, or extract oil. The vital nutrients, including proteins, sugar, and fat, are removed from the grains during the process, but what remains are the by-products that are fed to cows.
The four compartments’ efficient action and the bacteria in the rumen make these by-products edible for cows. This is why farmers and dairy staff can manage their herds for beneficial milk and meat production for human consumption.
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Bryan Harding is a member of the American Society of Mammalogists and a member of the American Birding Association. Bryan is especially fond of mammals and has studied and worked with them around the world. Bryan serves as owner, writer, and publisher of North American Nature.