Do Deer Chew Cud? (Explained)

Deer like to forage on readily available vegetation throughout the changing seasons. Vegetation such as shrubs, grasses, and leaves, have cellulose in them. Cellulose is difficult to break down and digest for many creatures.

Deer chew cud as a way to break down cellulose in fibrous plant material. They have a digestive system with a four-chambered stomach. Plant materials are broken down through grinding and chewing and then mix with microorganisms in the first two stomach chambers. This material is regurgitated as cud, for rechewing until it is small enough to pass into the other chambers for further digestion and nutrients. 

Read on to learn in more detail about the digestive process of the deer, as well as the role of diet in a deer’s survival.

Deer Chewing Cud

Deer are ruminants, a class of even-toed, cud-chewing, herbivore animals. Other examples of ruminant animals are cattle, giraffes, antelopes, and sheep. 

Eating patterns can vary by species, but deer can spend 40% to 60% of their time foraging for and intaking food.

Ruminants have multi-chambered stomachs that allow them to regurgitate chewed food (cud) to further break it down. 

Regurgitated cud, also called bolus, is chewed food that has been partially digested and is about the size of a lemon.

Species vary in the number of times they chew the cud. For example, a mule deer (Odocoileus hemionus) has an average of 56 chews.

This video shows a deer chewing cud. It also shows the movement of the deer’s throat as the cud moves down and then back up:

Mouth Anatomy

The anatomy of a deer’s mouth allows it to effectively obtain and chew food

They have incisor and canine teeth that help them grab and break food, such as grasses, agricultural crops, and other vegetation. 

The jaw musculature allows the deer to move lower teeth across upper back teeth in a side-to-side motion.

However, deer do not have front teeth (upper canines) at the top front part of their mouth.

Instead, they have a rough and bony palate that helps them grip and rip plant material, such as leaves and fruits, off of branches, vines, and the ground.

The bony palate and teeth work in conjunction to apply pressure, breaking food apart.


The Digestive System Of The Deer

The complex digestive system of the deer then processes the food (cellulose) to obtain nutrition. 

Microbes that assist in the digestive process in animals like deer are called syntrophism. This process allows them to effectively convert long-chain sugar (polysaccharides) from plant material into protein.

The energy (proteins, fats, sugars) that are found in plant material is contained within the fibrous cell wall. To get this nutrition from plant material, the body needs to break down this cellular wall. 

Chewing starts this process, by increasing the surface area of the plant material and mixing it with saliva. The food is chewed the first time until it is small enough, when it then enters the esophagus (throat). 

Deer have a four-chambered stomach consisting of the rumen, reticulum, omasum, and abomasum.

Chamber 1: Rumen

Food first moves into the rumen and mixes with microbes. This part of the stomach is a holding tank for the chewed food fatty acids and sugars are also absorbed here from the fermentation process.

This storage vat allows the deer to hold a considerable amount of food. Once the rumen is full, typically after 1 or 2 hours of eating, the deer will then sit to chew the material in smaller amounts as cud.

Hiccups

The deer’s chest expands, creating a vacuum that pushes the bolus (cud) up into the esophagus. A slight hiccup pushes the food back into the mouth.

The deer pushes the cud against the palate and roof of its mouth, squeezing out and swallowing fluid before rechewing the plant material.

Often during the cud-chewing process, the deer will rest in a comfortable position on the ground.

Chamber 2: Reticulum

Chyme (partially digested cud), will pass into the reticulum. 

The reticulum has a honeycomb pattern of ridges in its lining to further absorb volatile fatty acids (VFAs). Plant material continues to ferment in this chamber.

It is important to note that plant material can move between the rumen and reticulum, collectively called the reticulorumen, until it has been broken down for movement into other chambers. 

These two areas can hold several gallons

The process of digesting food in the reticulum can take over half a day or more depending upon how fibrous the plant material is.

Once food has been broken down small enough after repeated regurgitation and fermentation, the particles will move into the third chamber.

Chamber 3: Omasum

This chamber has a heavily-folded lining to absorb the majority of water, inorganic minerals, and any remaining VFAs. 

The remaining chyme then moves into the remaining, and last, chamber.

Chamber 4: Abomasum

The abomasum secretes gastric juices, such as hydrochloric acid, performing the majority of digestion. 

The digestion and absorption of proteins, fats, amino acids, and carbohydrates take place here.

Any remaining food particles then pass out of the last chamber of the stomach into the small and large intestines.

Intestines And Waste

Continued absorption of nutrients takes place in the intestines. 

Any remaining undigested material is then passed through as waste for the deer to eliminate in urine and droppings.


Deer Diet: Role In Digestion

Some plant material takes a long time to chew, break down, and digest to get nutrients.

The microorganisms in a deer’s digestive system can change depending upon the season and what is organically available. The size and lining of the rumen as well as the composition of the deer’s saliva change to accommodate this over a few weeks.

If a deer is eating human-provided food, such as hay, corn, or pellets, it cannot process and digest it fast enough. 

As a result, deer can starve even with a full rumen and reticulum. It is best to let deer eat what is naturally available as the seasons change.


In Conclusion 

Deer are cud-chewing herbivores with four-chambered stomachs.  

The chewing of cud allows the deer to break fibrous plant material down into small enough particles for digestion and nutrient absorption. Plant material will move repeatedly from the first two chambers back into the mouth for chewing until it is small enough.

The deer’s stomach contains microorganisms and gastric acids to further process food. The intestines uptake nutrients. 

Any remaining indigestible components are then eliminated as waste.

Deer must eat plant material that is seasonal and found naturally in the wild. Otherwise, they may eat something that they cannot digest quickly enough in order to survive.

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