White-tailed Deer Diet & Digestion
A white-tailed deer’s diet consists of a wide variety of herbaceous and woody plants, the ratio of one to the other being determined by the season. Fungi, fruits and herbaceous plants form much of the summer diet. Dried leaves and grasses, acorns, beechnuts and woody browse are important autumn and early winter food. After snowfall, the winter diet consists mostly of woody browse (twigs, leaves, shoots and buds) from many different trees (maples, birches and cedars among them). Come spring, deer eat buds, twigs and emerging leaves. Deer are ruminants (as are cattle, goats, sheep and moose). They have a four-chambered stomach, which is necessary in order to digest the cellulose in the vegetation they consume. Food goes first to the rumen, the first of the four chambers, which contains bacteria and other microorganisms that help digest the cellulose. Food is circulated from the rumen back to the deer’s mouth by the second chamber, or reticulum, and the deer ruminates (“chews its cud”). The third chamber, or omasum, functions as a pump, sending the food to the final chamber, the abomasum, where the digestion process is completed.
Naturally Curious with Mary Holland 
If the diet changes season to season is it harmful to feed deer corn in the winter? They seem to like my bird feeding area.
November 30, 2012 at 2:48 pm
Hi Renee,
As I understand it, deer ingest food and then bacteria in their rumen digest it. These populations of bacteria are somewhat specific to the type of food they breakdown. For example, if deer haven’t had access to corn, the bacteria that digest starchy foods significantly decrease in population. If a deer ingests a lot of corn while the appropriate bacteria populations are low, the corn can’t be digested and the deer will die with a stomach (or 4) full of corn. If the deer haven’t been consuming corn, then either don’t start or feed only very small amounts. The deer will literally have to grow the appropriate bacteria before gaining any benefit from the corn. As a rule of thumb, it’s best to let wildlife fend for themselves, as the balance of nature can so easily get out of whack.
November 30, 2012 at 7:14 pm
Mary, do you know how long it takes the deer to digest one feeding?
November 30, 2012 at 3:22 pm
No, I don’t, Lindsay, but I did find out that: “A deer goes to the bathroom” an average of 13 times every 24 hours. Usually 65 percent of the food will be used by the animal, and 5 percent is lost as methane gas, 5 percent as urine, and 25 percent as feces.”
November 30, 2012 at 7:32 pm
It is also important to recognize that changes take place in the deer’s digestive system with the seasons. In the winter, it is futile to “help” the deer by putting out things like bales of hay as the system is geared to digest woody twigs at this point, not herbaceous grass.
November 30, 2012 at 4:04 pm
Hi Tarun,
Thank you for your email. I was going to mention that, but when I researched it, I found that in fact, deer can adapt to diet other than a woody one, but it takes a couple of weeks, and meanwhile, they could well starve to death.
November 30, 2012 at 7:07 pm
Hello again, Mary,
An interesting thing about our white-tailed deer on Isle au Haut is that they have learned to eat rockweed when all else fails them in the winter. Our forests are almost all spruce, which the deer do not like, and the deer keep most other herbaceous plants eaten down to nubbins. 9However, the recent advent of coyotes, who swam over (island hopping about 6 miles) to establish a breeding population in recent years has seemed to reduce the deer population somewhat. As a result, we seem to have more wildflowers and hardwood saplings than we are used to.) Anyhow, deer have been seen down on the tideflats at low tide eating seaweed.
December 2, 2012 at 12:20 am
Thank you for telling us about deer digestion! My daughter Charlotte (age 5) loves to learn from your wonderful blog posts. We cannot believe how many new things you teach.
Peace,
Etienne & Charlotte
December 2, 2012 at 12:39 am