How Many Stomachs Does a Deer Have?

The deer species have a unique four-chambered stomach to aid in the way deer feed. The four chambers of a deer’s digestive system are known as:

· The rumen
· The reticulum
· The omasum
· The abomasum

How Many Stomachs?

Each of these four stomachs serves a different purpose to help a deer’s digestive system operate properly. The digestion process of a deer is extraordinarily complex and incredibly unique. It allows for maximum absorption of nutrients and water.

Deer and other animals with a four-chambered stomach are known as ruminant animals. Through these chambers, with the help of hydrochloric acid, the complex matter deer eat is broken down.
Let’s examine how each compartment of this four-chambered stomach works.

How Does Each Chamber of a Deer Stomach Function?

The following list is a description of how each chamber of a deer’s stomach works. Each of these stomach chambers serves to complete a unique function when digestion occurs.

Digestive Overview

The Rumen: First Chamber

The rumen is the first chamber in the four stomachs of a deer’s digestive system. This is the largest of all four chambers and is primarily used for storage. The size of the rumen allows deer to graze on massive amounts of plant matter in a short period. This is needed for a deer since they chew incredibly fast. Regardless of the significant size of the rumen, a deer can fill this compartment in as little as two-hours.

After the deer fills this compartment, they will rest and bring the chewed food back up to their mouth for a re-chew. This is known as “chewing cud” and further aids in the digestion process of plant matter.

The Reticulum: Second Chamber

The next chamber in the series of compartments on the deer species is known as the reticulum. Many individuals consider the reticulum as part of the rumen; however, they are separate. This chamber sits directly beneath the rumen and has an interior lining that’s very similar to a honeycomb.

This chamber of the stomach has microorganisms that help to break the food down even more. The chewed cud passes to the reticulum where digestion finally begins. The microorganisms begin working on the food to start fermentation.

When the food can ferment, it’s much easier to break down the cellulose within the items the deer eats. The fermentation process creates large levels of methane gas, which cause the deer to burp during digestion.

The Omasum: Third Chamber

The omasum is the spherical third chamber in the digestive system. This chamber has folds that make it look like the pages of a book. These folds increase the surface area of the digestive system, allowing the deer to obtain more nutrients during digestion.

Water also enters the fold during this part of digestion. Microorganisms that may have escaped are absorbed into the water, and this aids in the final steps of the process.

The Abomasum: Fourth Chamber

The abomasum is what is known as the true stomach of the deer. This is the part that is most like a normal stomach found in any species that has a single chambered digestive system. Inside of this chamber are enzymes and acids that are found in a normal stomach that help complete the digestion process.

Pepsin, pancreatic lipase, and other acids are contained in this chamber to help break down proteins. They also act as enzymes to aid the deer in breaking down any fat content found within their diet. Additionally, these enzymes and acid help break the food down so they can be absorbed into the small intestines for more nutrition.

The abomasum is one of the most complex compartments. This is mostly because the small and large intestines are considered a part of this portion.

Small Intestines

Once the food arrives at the small intestines, it’s mixed with the acid and enzymes that were released from the liver. These will increase the pH levels of the food which is vital for continuing the digestion process through the entirety of the intestines.

Bile juice from the gallbladder will also help the deer in further nutrient absorption. The whole surface of the intestines will allow nutrient absorption during the entire process.

Large Intestines

The large intestines help with absorbing water from the food that is digested. Once their body absorbs the added water, they secrete the remaining solid matter as feces. The colon is where most of the water absorption takes place, which is found at the bottom of the large intestines.

The fact that deer absorb most of the water during the digestion process leads to the exceptionally dry look of deer scat. Nearly 99% of all the water in a deer diet ends up being absorbed by their body in this incredible digestion process.

Forage Feeders vs. Grain Feeders: Digesting Carbs

Deer are typically either considered forage feeders or grain feeders. What’s the difference between deer and other ruminants in regard to the breakdown process?

Forage Feeding Instructions

The digestive process of a forage feeder differs slightly from that of a grain feeder. They ruminate ingested foods to reduce the size of the particles contained in their meals. This results in a faster digestion process.

The forage is exposed to microbes to break down the complex material. This also increases the flow of saliva during the digestion process, which balances out the pH levels in the deer.

Grain Feeders

Grain feeding deer extract carbs for energy in a different manner. Grain requires less chewing, so the need for saliva isn’t quite as heavy. Less gas is also produced during the grain feeding breakdown. However, higher levels of acid may be produced, which may lead to ulcers in the deer stomach.

Digesting Protein

Extracting protein from the food of a deer isn’t as complicated as extracting carbs. The proteins ingested through the four-chambered process are divided into degradable intake protein and undegradable intake protein.

Degradable Intake Protein

This is the primary method of protein ingestion for a deer. Rumen microbes build proteins that are later digested when food reaches the small intestines. These are then broken down into amino acids and peptides.

Added ammonia is directed to the liver where it is excreted as urine. This is why deer urine has such a strong smell.

Sometimes there is a small chance of toxicity because of the ammonia that is produced during digestion. However, this only occurs in deer that tend to overeat.

Undegradable Intake Protein

These materials are not able to degrade and aren’t dealt with until they reach the abomasum. Much of this material is washed out with the microorganisms in the rumen. The only material used by the animal is what arrives in the small intestines.

After this material is processed in the small intestines, it can be used as an energy source by the deer. Only a small fraction of these proteins ends up being used.


The digestion process for a deer is complex but it isn’t hard to understand when the multiple compartments are mapped out. This process is remarkably similar to that of a cow, and this is primarily because of the similarities in their diet at times. To digest large amounts of plant life, food must be broken down several times more than most animals.
Becoming an efficient hunter means making yourself familiar with the four chambers of a deer stomach and digestion. When you make your first kill, you’ll also have to process the animal and know your way around the anatomy to harvest the meat properly.

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