Deer Digestion: How it works and why feeding deer could lead to their death

By Alysia Wolf, Wildlife Biologist

All deer species are herbivores that, depending on their range and the season, will forage on native shrubs, grasses, twigs, leaves, and berries. Basically, plant parts. These plant parts are made up of cellulose, a molecule that humans can’t digest. The weird thing is, deer can’t digest cellulose, either. So why are they eating it and how are they surviving on it?

In large part, it comes down to a symbiotic relationship with microorganisms that live in the deer’s specialized digestive system. These microorganisms are able to digest cellulose. The deer provide the plants, the microorganisms break it down into a form that the deer can digest.

How exactly does this happen?

Deer eat fast. When they’re out eating, they chew their food just enough to swallow it, then the food enters the 1st chamber of the deer’s 4 chambered stomach.

That first chamber is known as the rumen. It’s the storage space within the deer’s stomach. They’ll eat their fill, then go find a safe place to sit and digest their food at a later time.

Deer bring the food back up into their mouth and chew it again. This is known as chewing their cud. It’s also called ruminating, and animals that do this are called ruminants.

When the deer swallows the food for the second time, it enters the 2nd chamber of the stomach called the reticulum. This is where those microorganisms live. They attack the chewed food in a process known as fermentation. This is when that indigestible cellulose is broken down into a simpler form that the deer can digest. (Fun fact: fermentation produces the gas methane, which the deer must discharge regularly by burping, or, you know…)

The cud is then regurgitated and chewed for a second time. When it’s swallowed this time around, it enters the 3rd chamber of the stomach known as the omasum. This is where water is absorbed. Next, the cud enters the last chamber, the abomasum, where the food is further digested by gastric juices. Gastric juices are liquids, like the acids in our stomachs, that help digest food.

Finally, the food moves on to the intestines. That’s when it’s absorbed by the deer’s body and the deer receives all of the nutrients. Once all possible nutrients are absorbed, the rest are passed as waste droppings.

But wait, it’s not as simple as all that.

A deer can starve to death with a full stomach.

Because certain types of plant matter can take so long to digest, the deer could feasibly die of starvation while waiting for the body to process the nutrients.

The microorganisms in deer digestive systems gradually change throughout the year and are specific to the food that is naturally available. As the seasons change, so do the plants that are available as food for deer. Eating different foods with each season means the deer’s digestive structures have to change in order to process the nutrients. Things such as the amount of saliva a deer produces and the size and lining of the  rumen change from one season to the next.

This change is not instant. It takes a few weeks for a deer’s stomach to adapt.

If a deer fills its stomach with hay, corn, or wet cob—products people use to artificially feed deer, and the deer don’t have enough of the hay- and corn- digesting microorganisms in their gut to digest the food, they can starve to death with a full stomach.

Feeding deer can also spread disease. Being abnormally close to one another allows contagious diseases or parasites to spread more easily through direct contact and even through saliva.

Wildlife officials have also seen evidence of highly contagious chronic wasting disease infected deer utilizing feeding stations. To learn more about this, visit

https://www.deseret.com/utah/2020/2/8/21128507/dont-feed-deer-wildlife-division-wildlife-reseouces