How Many Stomachs Do Deer Have?

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A deer has a four-chambered stomach: Rumen, Reticulum, Omasum, and Abomasum. These chambers all serve different purposes in its digestive system and sum up to easy digestion of feed ingested by the deer.

How Do the Four Chambers of a Deer’s Stomach Function?


The rumen is the first chamber in a deer’s digestive system. It is the largest component of the four and is mainly for storage. Its large capacity enables the deer to gather a massive amount of feed at a short period, and later digestion occurs. The deer is a fast chewer and only chews food enough to swallow. Depending on the quantity and type of food, a deer can fill this large room in less than two hours.

Later on, when the deer is resting, it brings back the food to its mouth, chewing it again. This second chewing is known as chewing cud, and the deer takes it time as it reduces the size of the food particles and swallows them again. Animals that “chew cud” are ruminants, the deer is no exception.


The reticulum is the second chamber of a deer’s stomach. It immediately follows the rumen, and most hunters consider these two as one organ. It sits underneath, front of the rumen, and is separated only by a small tissue fold. Its lining structure is similar to a honeycomb, and some even refer to it by that name.

It contains microorganisms such as microbes that aid in digestion. The chewed cud does not return to the rumen; instead, it passes through to the reticulum where digestion begins. Immediately it arrives in the reticulum, microbes attack the food, and kick start fermentation.

Fermentation of this chewed food helps in breaking down the complex cellulose into simpler forms, allowing it to digest. Methane gas is a result of the fermentation process, which brings the deer to burp.

The primary function of the reticulum is to collect smaller digesta particles, moving them to the third chamber of the deer’s digestive system.


The omasum is the third chamber found in a deer’s digestive system. It is spherical and connects to the reticulum by a short tunnel. It folds similarity to book pages, and most individuals refer to it as the “butcher’s bible.”

These folds do have a crucial purpose in the digestion process of a deer’s food. They increase the surface area of the absorption of nutrients from food and water ingested by the deer. Water absorption occurs in this chamber, and the size of the organ is directly proportional to the animal’s size. Microorganisms that may have been extracted from the reticulum are also absorbed with the water.


The abomasum is the final chamber, and it is the true stomach of a deer. This chamber is similar to the single stomach found in non-ruminants, with most of their functions being similar. Within this chamber is where you find hydrochloric acid and enzymes that help in digestion.

These enzymes include pepsin, which primary responsibility is breaking down proteins. Enzymes like pancreatic lipase, which usually secrete from the liver, also find their way to the abomasum. Here they act as enzymes responsible for breaking down fat present in the deer’s feed. These acids and enzymes help in preparing the proteins for absorption in the intestines.

The small and large intestines are the next stop for the digesta and are considered as part of the abomasum.

Small Intestines

The digesta arrives in the small intestines and is mixed with secretion from the liver and pancreas. These secretions are pepsin and lipase, respectively, as they play a massive role in the digestion process. They are responsible for the increase in pH levels that reach eight from 2.5. The high pH value is necessary for small intestines to continue with digestion successfully.

The first section of the small intestines contains bile juice from the animal’s gall bladder. There is active nutrient absorption in the whole surface area of these intestines. The presence of villi on its inner surface is an advantage as it increases the surface area for nutrient absorption, among other benefits.

Large Intestines

Large intestines are responsible for the absorption of water from the food ingested. After absorbing most of the water, they then excrete the remains as feces from the rectum. At the beginning of these intestines, there is a large blind pouch called the cecum. The cecum does not play a vital role in deer as it does in horses and other ruminants.

The colon is where most water absorption occurs in the large intestines.

Carbohydrate Digestion in Deer

Forage Feeders

Some of the deer species are heavy forage feeders, and their digestive system slightly differs in the digestion and extraction of energy from them. These species often ruminate their ingested foods allowing them to reduce the particle sizes of the materials, which result in a quicker and successful digestion process.

In the first chamber, after chewing, the forage is exposed to microbes. They offset fermentation and break down all the complex forms taken by these feeds into sugars and carbohydrates. The microbes ferment the sugar further, resulting in the production of methane and carbon dioxide in the animal. VFAs are also produced in this extended process.

The rumen walls absorb these VFAs produced and find their way to the liver. In the liver, gluconeogenesis occurs. This process converts these absorbed materials to glucose, which provides energy to the said animal. Routine rumination increases salivary flow in the digestive system, resulting in a stable pH environment favoring digestion.

Grain Feeders

Grain feeding members of the deer family extract carbs from their food differently. Since grains do not require intense chewing, there is less saliva flow in their systems. Most of these grains are highly concentrated with readily digestible carbohydrates. Carbohydrates increase VFA production; proportionate is the leading in quantity produced among the other VFAs.

The quantity of gasses produced in comparison to forage feeder digestion is less. An acidic environment of pH 5.5 is reached; however, when paired with lactic acid, they are harmful to the deer. This combination leads to ulceration of rumen tissue walls, and some extent, it is fatal.

Protein Digestion in Deer

The process of extracting proteins from a deer feed is not that complicated. A deer digestive system is well adapted to ensure that it extracts maximum protein nutrients from any ingested foods. The proteins ingested by most ruminants are divided into two; Degradable Intake Protein (DIP) and Undegradable Intake Protein (UIP). Each plant has different proportions of these proteins.

Degradable Intake Protein

This fraction is the primary source of proteins in most deer species. Rumen microbes use this fraction to build their proteins, which are later digested in the small intestines. The microbes break them down into ammonia amino acids and peptides.

Excess ammonia is absorbed through the rumen walls and directed to the liver. Here it converts to urea and is excreted. Toxicity is common when the excess ammonia overwhelms the liver’s ability to detoxify it. This toxicity is very rare and only occurs from animal overfeeding.

Undegradable Intake Protein

This fraction of ingested proteins remains intact through the entire system until it reaches the small intestines. The rumen and the other chambers are not able to degrade these proteins, as it passes them and is finally acted upon in the abomasum. The ruminant can use this fraction as a source of energy once it is processed in the small intestines.

Not the whole fraction is acted upon as some of it is washed out with other microorganisms from the rumen. The percentage that arrives in the small intestines is the only one used by the animal.

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From this article, we can conclude that a deer has four stomachs. These stomach chambers are the rumen, reticulum, omasum, and abomasum. Each of these chambers has a specific role to partake in for the digestion process to be complete. The. 

Each of these sections is a necessity for the deer to be able to break down complex materials like cellulose. Enzymes and acids also play a vital role in the digestive process of the Cervidae family. The number of acids available in this system is numerous, each having its unique responsibility.

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