Ask The Biologist

It’s Complicated

It’s Complicated

By Bob Humphrey

Whitetail digestion isn’t rocket science, but it’s close.

QUESTION: Someone recently told me that deer have four stomachs. Is this true?

ANSWER: No. Like all mammals, deer have one stomach. However, like all ruminants, theirs consists of four chambers: rumen, reticulum, omasum and abomasum.

A large portion of a whitetail’s diet is made up of coarse, woody browse. Because this browse is high in cellulose (fiber) and difficult to digest, deer need a more complex digestive system.

The first two chambers, the rumen and reticulum function similarly in two ways. First, they serve as a large storage container, allowing deer to consume a large quantity of food in a short time. The deer then retire to a safer area, bed down and bolus or cud the food, which they chew to physically break it down further.

It is then re-ingested into the first two chambers, where microflora including beneficial bacteria and protozoans further digest the food before it passes into the next chamber, the omasum, which has folds that allows smaller food particles to selectively pass into the true stomach or abomusum, where nutrients from the food can be absorbed into the body.

Because they have such a complex system that relies on microflora for digestion, drastic changes in diet, like sudden availability or absence of supplemental food, can actually be harmful to deer. That’s the reason you see articles asking that you not start or stop a feeding program suddenly, especially in winter environments where deer might be visiting a feeding site more often.

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